text:
Not fully—at least not in a way that is universally accepted.

What we can say confidently:

- **Consciousness depends strongly on brain activity.** Changes to the brain through sleep, anesthesia, injury, drugs, seizures, or stimulation reliably change conscious experience.
- **Neuroscience has identified many neural correlates of consciousness**, such as activity patterns involving the cortex, thalamus, brainstem arousal systems, and large-scale brain networks.
- **Some aspects of consciousness are increasingly explainable** in brain-based terms: perception, attention, memory, self-monitoring, decision-making, and reportability.

But there is still a major open question:

- **Why should brain activity feel like anything from the inside?**
  This is often called the “hard problem” of consciousness. Even if we map every neural process associated with seeing red, feeling pain, or being aware of oneself, some philosophers and scientists argue that we still have not explained why those processes produce subjective experience at all.

There are several competing views:

1. **Physicalism/materialism:** Consciousness is entirely produced by brain activity, even if we do not yet understand how.
2. **Dualism:** Mind or consciousness is not reducible to physical brain processes.
3. **Panpsychism:** Consciousness, or proto-consciousness, is a basic feature of matter.
4. **Emergentism:** Consciousness emerges from complex brain organization in a way that is real but dependent on physical processes.
5. **Illusionism:** Our sense of having private subjective experience may itself be a cognitive construction.

So the best current answer is:

**Brain activity is the best-supported basis for consciousness, and it explains many features of conscious experience, but whether it fully explains subjective awareness remains unresolved.**


prompt_id: sci-consciousness

provider: openai

text:
Not fully—at least not in a way that everyone agrees is complete.

**What neuroscience has shown strongly:**
Consciousness is tightly linked to brain activity. Changes in the brain—sleep, anesthesia, seizures, brain injury, drugs, stimulation—reliably alter or eliminate conscious experience. Specific brain networks appear crucial for attention, awareness, perception, memory, and selfhood. So any scientific account of consciousness must heavily involve brain activity.

**What remains unresolved:**
Neuroscience can increasingly explain *which* brain processes correspond to conscious states and *how* information is integrated, attended to, reported, or used in behavior. But there is still debate over whether this fully explains the *subjective feel* of experience—why brain activity is accompanied by “what it is like” to see red, feel pain, or be oneself. This is often called the **hard problem of consciousness**.

**Major views include:**

- **Physicalism/materialism:** Consciousness is entirely produced by or identical with brain activity, even if we do not yet understand the details.
- **Dualism:** Consciousness involves something nonphysical in addition to the brain.
- **Panpsychism:** Consciousness or proto-consciousness is a basic feature of matter.
- **Emergentism:** Consciousness arises from complex brain organization but is not easily reducible to individual neural events.

**Best short answer:**
Brain activity explains a great deal about consciousness and is almost certainly necessary for normal human consciousness. But whether it *fully* explains subjective experience remains an open scientific and philosophical question.

finish_reason: stop


text:
Not conclusively.

From a scientific standpoint, consciousness is **deeply dependent on brain activity**: changes in neural activity reliably correlate with changes in perception, attention, memory, self-awareness, anesthesia, dreaming, coma, and so on. Most neuroscientists assume that consciousness arises from or is implemented by brain processes, and several theories try to explain how, such as **Global Workspace Theory**, **Integrated Information Theory**, and **predictive processing**.

But whether consciousness is **fully explained** by brain activity is still disputed.

There are two broad questions:

1. **The “easy” scientific questions**
   How does the brain integrate information? How does attention work? How do we report experiences? What neural patterns correspond to seeing red, feeling pain, or being awake?
   These are difficult but tractable, and neuroscience has made major progress.

2. **The “hard problem” of consciousness**
   Why should any physical brain process be accompanied by subjective experience at all? Why is there “something it is like” to feel pain or see color?
   This remains philosophically unresolved.

So the cautious answer is:

**Brain activity appears necessary for human consciousness and explains many of its features, but we do not yet have a complete explanation of why or how subjective experience arises from it.**

A physicalist would say consciousness will eventually be fully explained by neuroscience. A dualist, panpsychist, or non-reductive philosopher may argue that brain activity alone cannot fully account for subjective experience. The current evidence strongly links consciousness to the brain, but the deeper explanatory question remains open.


text:
Not fully—at least not in a way that everyone agrees is complete.

What we can say confidently:

- **Consciousness is tightly linked to brain activity.** Changes to the brain through sleep, anesthesia, seizures, injury, drugs, stimulation, or disease reliably change conscious experience.
- **Neuroscience has identified many neural correlates of consciousness**, such as activity in thalamo-cortical networks, fronto-parietal systems, recurrent processing, and global brain dynamics.
- **Some aspects are increasingly explainable**, like perception, attention, wakefulness, memory integration, and reportable awareness.

But there remains a major open question:

- **Why and how brain activity produces subjective experience at all**—the feeling of pain, the redness of red, the sense of being someone—is not yet fully explained. This is often called the **“hard problem” of consciousness**.

There are several positions:

1. **Physicalism/materialism:** consciousness is entirely produced by brain processes, even if we do not yet understand how.
2. **Dualism:** mind or consciousness is not reducible to physical brain activity.
3. **Panpsychism or neutral monism:** consciousness or proto-conscious properties are fundamental features of reality.
4. **Illusionism:** the sense of having ineffable subjective experience is itself a cognitive construction.

The mainstream scientific view is that **consciousness depends on the brain**, but whether brain activity gives a **complete explanation** of consciousness is still debated. So the best answer is:

**Brain activity explains a great deal about consciousness, and may ultimately explain all of it, but at present consciousness is not fully explained.**


text:
Not conclusively.

**What we can say with high confidence:**
Consciousness is deeply tied to brain activity. Changes in the brain reliably alter conscious experience: anesthesia, sleep, brain injury, seizures, drugs, stimulation, and neurodegenerative disease all affect awareness, perception, memory, selfhood, and emotion. Neuroscience has identified many **neural correlates of consciousness**—patterns of brain activity associated with being conscious or having specific experiences.

**What remains unresolved:**
Whether brain activity **fully explains** consciousness depends on what “fully explains” means.

- If it means “Can we map which brain processes produce which conscious states?” then science has made major progress, but the map is incomplete.
- If it means “Can physical brain processes explain why subjective experience exists at all?”—the so-called **hard problem of consciousness**—there is no consensus.
- If it means “Is consciousness nothing over and above brain activity?” that is a philosophical position, often called **physicalism**, and many scientists and philosophers accept it, but it has not been definitively proven.

Major theories—such as **Global Workspace Theory**, **Integrated Information Theory**, **Higher-Order Thought theories**, and **predictive processing**—try to explain consciousness in terms of information processing, integration, attention, self-modeling, or brain-wide broadcasting. None is universally accepted.

So the best current answer is:

**Consciousness is strongly dependent on brain activity, and brain activity explains many features of consciousness. But whether it fully explains subjective experience remains an open scientific and philosophical question.**


prompt_id: sci-evolution

text:
Evolution by natural selection is the process by which living populations change over generations because individuals with certain inherited traits survive and reproduce more successfully than others.

It works through a few key steps:

1. **Variation exists**
   Individuals in a population are not all identical. They differ in traits such as size, color, speed, disease resistance, behavior, or metabolism.

2. **Some variation is inherited**
   Many traits are influenced by genes and can be passed from parents to offspring.

3. **More offspring are produced than can survive**
   Because resources like food, space, and mates are limited, not every individual survives or reproduces.

4. **Some traits improve survival or reproduction**
   If a trait helps an organism survive or have more offspring in a particular environment, individuals with that trait are more likely to pass it on.

5. **Helpful traits become more common**
   Over many generations, traits that increase reproductive success tend to spread through the population. Traits that reduce success may become less common.

For example, imagine a population of beetles where some are green and some are brown. If birds can see green beetles more easily on the ground, brown beetles may survive more often and produce more offspring. Over generations, the population may become mostly brown.

Natural selection does **not** mean that organisms try to evolve or that evolution has a goal. The environment “selects” among existing variations by affecting which individuals leave more descendants.

Over long periods of time, natural selection can lead to adaptations, new species, and the diversity of life seen on Earth.


text:
Evolution by natural selection is the process by which populations of living things change over generations because some inherited traits help organisms survive and reproduce better than others.

Here’s the basic idea:

1. **Variation exists**
   Individuals in a population are not all identical. They may differ in size, color, disease resistance, behavior, speed, and many other traits.

2. **Some variation is inherited**
   Many traits can be passed from parents to offspring through genes.

3. **More offspring are produced than can survive**
   Organisms often produce more young than the environment can support, so there is competition for food, space, mates, and other resources.

4. **Some traits improve survival or reproduction**
   Individuals with traits that are better suited to their environment are more likely to survive long enough to reproduce, or to produce more offspring.

5. **Helpful traits become more common**
   Because those individuals leave more offspring, the genes linked to helpful traits become more common in the population over time.

Over many generations, this can lead to major changes in a population. Sometimes, if groups of the same species become separated and evolve differently, they may eventually become distinct species.

A classic example is antibiotic resistance in bacteria. Some bacteria may naturally have mutations that let them survive an antibiotic. When the antibiotic is used, susceptible bacteria die, while resistant ones survive and reproduce. Over time, the bacterial population becomes mostly resistant.

Natural selection does not mean organisms “try” to evolve. The variation already exists or arises by mutation, and the environment influences which traits are more successful.


text:
Evolution by natural selection is the process by which populations of organisms change over generations because some inherited traits help individuals survive and reproduce better than others.

It works through a few key steps:

1. **Variation exists**
   - Individuals in a population are not identical.
   - They differ in traits such as size, color, speed, disease resistance, or behavior.

2. **Some variation is inherited**
   - Many traits can be passed from parents to offspring through genes.

3. **More offspring are produced than can survive**
   - Organisms often produce more young than the environment can support.
   - This creates competition for food, space, mates, and other resources.

4. **Some traits improve survival or reproduction**
   - Individuals with traits that are better suited to their environment are more likely to survive and have offspring.
   - This is called **natural selection**.

5. **Helpful traits become more common**
   - Because successful individuals pass on their genes, advantageous traits tend to increase in frequency over generations.

Over long periods of time, this can lead to major changes in a population and even the formation of new species.

For example, if a population of insects includes both light and dark individuals, and birds can more easily see the light insects on dark tree bark, the dark insects may survive and reproduce more often. Over generations, the population may become mostly dark-colored.

Natural selection does not mean organisms “try” to evolve. Instead, evolution happens because individuals with certain inherited traits leave more descendants than others.


text:
Evolution by natural selection is the process by which populations of organisms change over generations because some inherited traits help individuals survive and reproduce more successfully than others.

It works through a few key steps:

1. **Variation exists in a population**
   Individuals in a species are not all identical. They differ in traits such as size, color, speed, resistance to disease, or ability to find food. Much of this variation comes from genetic mutation and recombination.

2. **Some traits are inherited**
   Many traits can be passed from parents to offspring through genes. If a trait is not heritable, natural selection cannot directly make it more common in future generations.

3. **More offspring are produced than can survive**
   Organisms often produce more young than the environment can support. Because food, space, mates, and other resources are limited, individuals face competition and environmental pressures.

4. **Some traits improve survival or reproduction**
   Individuals with traits that are better suited to their environment may be more likely to survive, attract mates, or produce offspring. This is called **differential reproductive success**.

5. **Helpful traits become more common over generations**
   If those advantageous traits are inherited, the genes associated with them become more frequent in the population. Over many generations, this can lead to significant changes in the population.

For example, if a population of insects is exposed to a pesticide, a few may happen to have genetic resistance. Those resistant insects survive and reproduce, passing resistance to their offspring. Over time, the population may become mostly pesticide-resistant.

Natural selection does **not** mean individuals choose to adapt or that evolution has a goal. Instead, individuals with certain inherited traits happen to leave more offspring in a particular environment. The population evolves; individual organisms do not evolve during their lifetimes.


text:
Evolution by natural selection is the process by which living populations change over generations because individuals with certain inherited traits survive and reproduce more successfully than others.

It works through a few key steps:

1. **Variation exists**
   Individuals in a population are not all identical. They differ in traits such as size, color, speed, disease resistance, or behavior.

2. **Some variation is inherited**
   Many traits can be passed from parents to offspring through genes.

3. **More offspring are produced than can survive**
   Organisms often produce more young than the environment can support, leading to competition for food, mates, space, and other resources.

4. **Some traits improve survival or reproduction**
   In a particular environment, certain inherited traits may give individuals an advantage. For example, a camouflaged insect may be less likely to be eaten by predators.

5. **Those traits become more common**
   Individuals with advantageous traits are more likely to survive, reproduce, and pass those traits to their offspring. Over many generations, the traits become more common in the population.

This gradual change in populations over time is evolution.

A classic example is antibiotic resistance in bacteria. Some bacteria may naturally have genetic variations that let them survive an antibiotic. When the antibiotic kills the susceptible bacteria, the resistant ones survive and reproduce. Over time, the bacterial population becomes mostly resistant.

Natural selection does not have a goal or plan. It simply favors traits that help organisms survive and reproduce in their current environment. If the environment changes, different traits may become advantageous.


text:
Evolution by natural selection is a process that explains how populations of living things change over generations and become better adapted to their environments.

It works through a few key steps:

1. **Variation exists**
   Individuals in a population are not all identical. They differ in traits such as size, color, speed, disease resistance, or behavior.

2. **Some variation is inherited**
   Many traits are passed from parents to offspring through genes.

3. **More offspring are produced than can survive**
   Organisms often produce more young than the environment can support. This leads to competition for food, space, mates, and other resources.

4. **Some traits improve survival or reproduction**
   Individuals with traits that help them survive or reproduce in a particular environment are more likely to pass those traits on.

5. **Helpful traits become more common**
   Over many generations, traits that increase reproductive success tend to spread through the population.

For example, if a population of insects includes some green individuals and some brown individuals, and birds more easily see the green ones on tree bark, the brown insects may survive more often. If color is inherited, brown insects will leave more offspring, and over time the population may become mostly brown.

Natural selection does **not** mean organisms choose to change, and it does not always produce “perfect” organisms. It simply means that inherited traits affecting survival and reproduction become more or less common depending on environmental conditions.

Over long periods of time, natural selection can lead to major changes, including the formation of new species.


text:
Evolution by natural selection is the process by which populations of living organisms change over generations because some traits help individuals survive and reproduce more successfully than others.

It works through a few key steps:

1. **Variation exists**
   - Individuals in a population are not identical.
   - They differ in traits such as size, color, speed, disease resistance, or behavior.

2. **Some variation is inherited**
   - Many traits can be passed from parents to offspring through genes.

3. **More offspring are produced than can survive**
   - Organisms often produce more young than the environment can support.
   - This creates competition for food, mates, shelter, and other resources.

4. **Some traits give an advantage**
   - Individuals with traits better suited to their environment are more likely to survive and reproduce.
   - For example, a camouflaged insect may be less likely to be eaten by predators.

5. **Advantageous traits become more common**
   - Because successful individuals leave more offspring, the genes for helpful traits become more frequent in the population over time.

Over many generations, these small changes can accumulate, causing populations to become better adapted to their environments. If populations become different enough, new species can eventually form.

A classic example is antibiotic resistance in bacteria. Some bacteria may naturally have mutations that let them survive an antibiotic. When the antibiotic kills the susceptible bacteria, the resistant ones survive and reproduce. Over time, the bacterial population becomes mostly resistant.

Natural selection does not mean organisms “try” to evolve. Instead, evolution happens because inherited traits affect survival and reproduction in a particular environment.


text:
Evolution by natural selection is the process by which populations of living organisms change over generations because individuals with certain inherited traits survive and reproduce more successfully than others.

It works through a few key steps:

1. **Variation exists**
   - Individuals in a population are not identical.
   - They differ in traits such as size, color, speed, disease resistance, or behavior.

2. **Some variation is inherited**
   - Many traits are passed from parents to offspring through genes.
   - For natural selection to affect evolution, the trait must be heritable.

3. **More offspring are produced than can survive**
   - Organisms often produce more young than the environment can support.
   - Because food, space, mates, and other resources are limited, not all individuals survive or reproduce.

4. **Some traits give an advantage**
   - Individuals with traits better suited to their environment are more likely to survive and reproduce.
   - This is often called “fitness,” meaning reproductive success, not necessarily physical strength.

5. **Helpful traits become more common**
   - If individuals with advantageous traits leave more offspring, those traits become more common in the population over many generations.

Over time, this can lead to major changes in a population. If different groups of the same species experience different environments or become separated, they may evolve in different directions and eventually become separate species.

For example, if a population of insects includes both green and brown individuals, and birds more easily see and eat the green ones in a brown environment, brown insects may survive and reproduce more often. Over generations, the population may become mostly brown.

Natural selection does not work toward a goal or make organisms “perfect.” It simply favors traits that help organisms survive and reproduce in a particular environment at a particular time.


text:
Evolution by natural selection is the process by which populations of organisms change over generations because individuals with certain heritable traits survive and reproduce more successfully than others.

It works through four main ideas:

1. **Variation**
   Individuals in a population are not all identical. They differ in traits such as size, color, speed, disease resistance, or behavior.

2. **Heritability**
   Some of these differences are genetic and can be passed from parents to offspring.

3. **Differential survival and reproduction**
   In a given environment, some traits help individuals survive or reproduce better. For example, an animal with better camouflage may be less likely to be eaten.

4. **Change over generations**
   Individuals with advantageous traits tend to leave more offspring. Over many generations, those traits become more common in the population.

A classic example is antibiotic resistance in bacteria. In a population of bacteria, a few may naturally have mutations that make them resistant to an antibiotic. When the antibiotic is used, susceptible bacteria die, while resistant ones survive and reproduce. Soon, the bacterial population contains mostly resistant bacteria.

Natural selection does not “try” to make organisms perfect. It simply favors traits that improve survival or reproduction in a particular environment. If the environment changes, different traits may become advantageous. Over long periods, this process can lead to adaptation and even the formation of new species.


text:
Evolution by natural selection is the process by which populations of organisms change over generations because individuals with certain heritable traits survive and reproduce more successfully than others.

It works through a few key steps:

1. **Variation exists**
   Individuals in a population are not all identical. They may differ in size, color, speed, disease resistance, behavior, and many other traits.

2. **Some variation is inherited**
   Many traits are influenced by genes and can be passed from parents to offspring.

3. **More offspring are produced than can survive**
   Organisms often produce more young than the environment can support, so there is competition for food, space, mates, and safety.

4. **Some traits improve survival or reproduction**
   Individuals with traits that are better suited to their environment are more likely to survive and have offspring.

5. **Helpful traits become more common**
   Because successful individuals pass on their genes, traits that improve survival or reproduction tend to increase in frequency in the population over many generations.

For example, if a population of beetles includes both green and brown individuals, and birds can more easily see and eat the green beetles, brown beetles may survive and reproduce more often. Over time, the population may become mostly brown.

Natural selection does not involve organisms “trying” to change. Instead, random genetic variation already exists, and the environment influences which traits are more successful. Over long periods, this process can lead to adaptation and even the formation of new species.


text:
Evolution by natural selection is the process by which populations change over generations because some inherited traits help organisms survive and reproduce better than others.

It works through a few key steps:

1. **Variation exists**
   Individuals in a population are not identical. They differ in traits such as size, color, speed, disease resistance, metabolism, or behavior.

2. **Some variation is inherited**
   Many traits are influenced by genes and can be passed from parents to offspring.

3. **More offspring are produced than can survive**
   Organisms often produce more young than the environment can support, leading to competition for food, mates, space, or other resources.

4. **Some traits improve survival or reproduction**
   Individuals with traits that are better suited to their environment are more likely to survive, find mates, and produce offspring.

5. **Helpful traits become more common**
   Because those individuals leave more offspring, the genes associated with advantageous traits tend to increase in frequency in the population over generations.

Over time, this can cause a population to become better adapted to its environment. If populations are separated or face different environmental pressures for long enough, they may eventually evolve into different species.

A simple example is **antibiotic resistance** in bacteria. Some bacteria may randomly have mutations that let them survive an antibiotic. When the antibiotic kills the susceptible bacteria, the resistant ones survive and reproduce. Soon, the population contains more resistant bacteria.

Natural selection is not intentional or goal-directed. Organisms do not evolve because they “need” to. Instead, random genetic variation arises, and the environment influences which variations are more successful.


text:
Evolution by natural selection is the process by which populations of living things change over generations because some individuals are better suited to their environment than others.

It works through a few key steps:

1. **Variation exists**
   Individuals in a population are not identical. They differ in traits such as size, color, speed, disease resistance, or behavior.

2. **Some variation is inherited**
   Many traits can be passed from parents to offspring through genes.

3. **More offspring are produced than can survive**
   Organisms often produce more young than the environment can support, leading to competition for food, mates, space, and other resources.

4. **Some traits improve survival or reproduction**
   Individuals with traits that help them survive or reproduce in a particular environment tend to leave more offspring.

5. **Helpful traits become more common**
   Because those individuals pass their traits to the next generation, the traits that improve survival or reproduction become more frequent over time.

Over many generations, this can lead to significant changes in a population. In some cases, populations may become so different that they form new species.

A classic example is camouflage. If insects vary in color, and birds more easily spot the lighter insects on dark tree bark, darker insects may survive and reproduce more. Over generations, the population may become mostly dark-colored.

Importantly, natural selection does not have a goal or plan. It simply favors traits that work well in a particular environment at a particular time. If the environment changes, different traits may become advantageous.


text:
Evolution by natural selection is the process by which populations of living organisms change over generations because some inherited traits help individuals survive and reproduce better than others.

It works through a few key steps:

1. **Variation exists**
   Individuals in a population are not all identical. They differ in traits such as size, color, speed, disease resistance, or behavior.

2. **Some variation is inherited**
   Many traits are passed from parents to offspring through genes.

3. **More offspring are produced than can survive**
   Organisms often produce more young than the environment can support, so there is competition for food, mates, space, and safety.

4. **Some traits improve survival or reproduction**
   Individuals with traits that are better suited to their environment are more likely to survive and have offspring. This is called “higher fitness.”

5. **Helpful traits become more common**
   Because successful individuals pass their traits to the next generation, those traits increase in frequency over time.

Over many generations, this can lead to major changes in a population. If populations become different enough, new species can eventually form.

A simple example: imagine a population of beetles that vary in color. If birds can more easily see and eat light-colored beetles, darker beetles may survive more often. Dark beetles then reproduce more, passing on genes for darker color. After many generations, the beetle population may become mostly dark.

Natural selection does not mean organisms “try” to evolve. Instead, random genetic variation already exists, and the environment “selects” which traits are more successful.


text:
Evolution by natural selection is the process by which populations of living things change over generations because individuals with certain inherited traits survive and reproduce more successfully than others.

It works through a few key steps:

1. **Variation exists**
   Individuals in a population are not all identical. They differ in traits such as size, color, speed, disease resistance, or behavior.

2. **Some variation is inherited**
   Many traits are passed from parents to offspring through genes.

3. **More offspring are produced than can survive**
   Organisms often produce more young than the environment can support. This creates competition for food, space, mates, and other resources.

4. **Some traits give an advantage**
   In a particular environment, certain traits may help individuals survive or reproduce better. For example, a better-camouflaged insect may be less likely to be eaten.

5. **Those traits become more common**
   Individuals with helpful inherited traits tend to leave more offspring. Over many generations, those traits increase in frequency in the population.

Over long periods of time, natural selection can lead to major changes in populations and may eventually contribute to the formation of new species.

A simple example is antibiotic resistance in bacteria. Some bacteria may randomly have mutations that let them survive an antibiotic. When the antibiotic kills the susceptible bacteria, the resistant ones survive and reproduce. Soon, the resistant type becomes more common.

Importantly, natural selection does not mean organisms “try” to evolve. Variation arises naturally, often through mutation and genetic recombination, and the environment “selects” which traits are more successful.


text:
Evolution by natural selection is the process by which populations of organisms change over generations because some inherited traits help individuals survive and reproduce better than others.

It works through a few key steps:

1. **Variation exists**
   Individuals in a population are not all identical. They may differ in size, color, speed, disease resistance, behavior, and many other traits.

2. **Some variation is inherited**
   Many traits are passed from parents to offspring through genes.

3. **More offspring are produced than can survive**
   Organisms often produce more young than the environment can support, so there is competition for food, space, mates, and other resources.

4. **Some traits give an advantage**
   Individuals with traits better suited to their environment are more likely to survive and reproduce. This is called **natural selection**.

5. **Helpful traits become more common**
   Because successful individuals leave more offspring, the genes for advantageous traits tend to increase in the population over generations.

For example, if a population of insects lives on dark tree bark, darker-colored insects may be harder for predators to see. Those insects survive and reproduce more often, so over time the population may become mostly dark-colored.

Natural selection does **not** mean organisms “try” to evolve or that evolution has a goal. Instead, the environment favors certain inherited traits, and populations gradually change as a result. Over very long periods, these changes can lead to new species.


text:
Evolution by natural selection is the process by which populations of organisms change over generations because some inherited traits help individuals survive and reproduce more successfully than others.

Here’s how it works:

1. **Variation exists**
   - Individuals in a population are not identical.
   - They may differ in size, color, speed, disease resistance, behavior, and many other traits.

2. **Some variation is inherited**
   - Many traits are passed from parents to offspring through genes.
   - Mutations, genetic recombination, and sexual reproduction create new genetic variation.

3. **More offspring are produced than can survive**
   - Environments have limited food, space, mates, and other resources.
   - Not every individual survives long enough to reproduce.

4. **Some traits improve survival or reproduction**
   - If a trait makes an organism better suited to its environment, individuals with that trait may leave more offspring.
   - For example, a camouflaged insect may be less likely to be eaten by predators.

5. **Helpful traits become more common**
   - Because individuals with advantageous traits reproduce more, the genes for those traits become more frequent in the population over time.

Over many generations, this can lead to major changes in a population. If populations become different enough, new species can eventually form.

A classic example is antibiotic resistance in bacteria. Some bacteria may randomly have mutations that let them survive an antibiotic. When the antibiotic kills the susceptible bacteria, the resistant ones survive and reproduce. Over time, the bacterial population becomes mostly resistant.

Importantly, natural selection does not give organisms traits because they “need” them. Instead, random variation already exists, and the environment “selects” traits that happen to be useful.


text:
Evolution by natural selection is the process by which populations of organisms change over generations because some inherited traits help individuals survive and reproduce better than others.

It works through a few key steps:

1. **Variation exists**
   Individuals in a population are not all identical. They differ in traits such as size, color, speed, disease resistance, or behavior.

2. **Some variation is inherited**
   Many traits are passed from parents to offspring through genes.

3. **More offspring are produced than can survive**
   Resources such as food, space, and mates are limited, so not every individual survives and reproduces.

4. **Some traits give an advantage**
   Individuals with traits that are better suited to their environment are more likely to survive, find mates, and produce offspring.

5. **Helpful traits become more common**
   Because advantageous traits are inherited, they tend to appear more often in the next generation.

Over many generations, this can cause a population to change significantly. This change is called **evolution**.

For example, if a population of insects includes both green and brown individuals, and birds can more easily spot the green ones on tree bark, brown insects may survive and reproduce more often. Over time, the population may become mostly brown.

Natural selection does not mean organisms “try” to evolve. Instead, individuals with certain inherited traits happen to survive and reproduce more successfully in a particular environment. If the environment changes, different traits may become advantageous.


text:
Evolution by natural selection is the process by which populations of living organisms change over generations because individuals with certain heritable traits survive and reproduce more successfully than others.

It works through a few key steps:

1. **Variation exists**
   Individuals in a population are not all identical. They may differ in size, color, speed, disease resistance, behavior, or many other traits.

2. **Some variation is heritable**
   Many traits are influenced by genes and can be passed from parents to offspring.

3. **More offspring are produced than can survive**
   Organisms often produce more young than the environment can support. This creates competition for food, space, mates, and other resources.

4. **Some traits improve survival or reproduction**
   If a trait helps an organism survive longer or produce more offspring in a particular environment, individuals with that trait are more likely to pass it on.

5. **Helpful traits become more common**
   Over many generations, traits that increase reproductive success tend to become more frequent in the population.

For example, imagine a population of beetles where some are green and some are brown. If birds more easily see and eat the green beetles, brown beetles may survive and reproduce more often. Over time, the population may contain more brown beetles.

Natural selection does not mean organisms “try” to evolve. It also does not produce perfect organisms. It simply favors traits that work better in a particular environment at a particular time.

Over long periods, natural selection can lead to major changes in populations and even the formation of new species.


text:
Evolution by natural selection is the process by which populations of organisms change over generations because individuals with certain inherited traits survive and reproduce more successfully than others.

Here’s how it works:

1. **Variation exists**
   - Individuals in a population are not all identical.
   - They differ in traits such as size, color, speed, resistance to disease, or ability to tolerate heat.

2. **Some variation is inherited**
   - Many traits are passed from parents to offspring through genes.
   - If a trait has a genetic basis, it can become more or less common in future generations.

3. **More offspring are produced than can survive**
   - Organisms often produce more young than the environment can support.
   - This creates competition for resources like food, space, mates, and shelter.

4. **Some traits improve survival or reproduction**
   - Individuals with traits that help them survive or reproduce in a particular environment tend to leave more offspring.
   - For example, a moth whose color better matches tree bark may be less likely to be eaten by birds.

5. **Helpful traits become more common**
   - Because successful individuals pass on their genes more often, the traits that helped them tend to increase in the population over generations.

Over long periods of time, natural selection can lead to **adaptations**—traits that are well suited to a particular environment. If populations become different enough, this process can also contribute to the formation of new species.

A key point is that natural selection does **not** happen because organisms “try” to evolve. Individuals do not evolve during their lifetimes in the evolutionary sense; **populations evolve across generations**.


text:
Evolution by natural selection is the process by which populations of organisms change over generations because individuals with certain inherited traits survive and reproduce more successfully than others.

It works through four main ideas:

1. **Variation**
   Individuals in a population are not all identical. They differ in traits such as size, color, speed, disease resistance, behavior, or metabolism.

2. **Inheritance**
   Some of these differences are genetic and can be passed from parents to offspring.

3. **Differential survival and reproduction**
   In a particular environment, some traits help individuals survive or reproduce better. Those individuals tend to leave more offspring.

4. **Change over generations**
   Because helpful traits are passed on more often, they become more common in the population over time. Less helpful traits may become less common.

For example, imagine a population of beetles where some are green and some are brown. If birds can see green beetles more easily, brown beetles may survive more often and produce more offspring. Over many generations, the population may contain more brown beetles.

A few important points:

- Natural selection acts on **individuals**, but evolution happens in **populations**.
- It does not have a goal or plan; it simply favors traits that work well in a given environment.
- A trait that is useful in one environment may be harmful or neutral in another.
- New variation arises through mutation, genetic recombination, and other genetic processes.

Over long periods of time, natural selection can lead to adaptation, the formation of new species, and the diversity of life seen on Earth.


prompt_id: sci-iq-heritability

text:
Human intelligence—as measured by IQ tests and related cognitive batteries—is **substantially heritable**, but not genetically fixed. The best-supported conclusion is that, in modern populations with typical ranges of schooling, nutrition, and health care, **genetic differences account for roughly half or more of individual differences in measured cognitive ability**, with estimates varying by age, population, and method.

## Short answer

- **Children:** heritability is often estimated around **20–40%**.
- **Adolescents:** around **40–60%**.
- **Adults:** commonly around **50–80%**, with many estimates near **60%**.
- **Environment still matters a lot**, especially early life environment, education, nutrition, disease burden, toxins, stress, and socioeconomic conditions.
- Heritability is **not determinism**: a highly heritable trait can still be changed by environment.

## What kind of evidence supports this?

### 1. Twin studies

Identical twins share ~100% of their DNA, while fraternal twins share ~50% on average. Across many studies, identical twins are more similar in IQ than fraternal twins.

Typical pattern:

- Identical twins raised together: very high similarity.
- Fraternal twins raised together: moderate similarity.
- Identical twins raised apart: still fairly high similarity, though not as high as those raised together.

This is strong evidence that genetic differences contribute substantially to variation in intelligence.

### 2. Adoption studies

Adoption studies show that adopted children’s IQs often resemble their adoptive families more in childhood, but as they grow older, their IQs tend to become more similar to those of their biological relatives.

This supports two points:

- Family environment matters, especially earlier in life.
- Genetic influence tends to become more apparent with age.

### 3. Molecular genetic evidence

Genome-wide association studies, or GWAS, have found thousands of DNA variants associated with cognitive performance and educational attainment. Each variant has a tiny effect, but collectively they predict some variation.

Important points:

- Intelligence is **highly polygenic**: influenced by many thousands of genetic variants.
- Common SNPs measured in GWAS account for a meaningful but incomplete portion of variation, often called **SNP heritability**, roughly around **20–30%** depending on the trait and sample.
- Polygenic scores can predict some cognitive and educational outcomes, but they are far from deterministic and are less accurate outside the populations in which they were developed.

## Why does heritability increase with age?

A common finding is that IQ heritability rises from childhood to adulthood. One explanation is **gene–environment correlation**: as people get older, they increasingly select, shape, or evoke environments that fit their dispositions. For example, a child with an early interest in puzzles or reading may seek out more cognitively stimulating activities, which further amplifies initial differences.

## What heritability does *not* mean

Heritability is often misunderstood.

A heritability estimate of 60% does **not** mean:

- 60% of a person’s intelligence is genetic.
- IQ cannot be changed.
- Environment is unimportant.
- Genetic differences explain differences between social, ethnic, or national groups.

Heritability refers to **variation within a specific population in a specific environment**. If environments change, heritability can change too.

For example, height is highly heritable, but average height has increased dramatically in many countries because of better nutrition and health. Similarly, IQ scores rose substantially during the 20th century in many places—the **Flynn effect**—showing that environmental changes can strongly affect cognitive test performance.

## Environmental influences are real

Factors known or strongly suspected to affect cognitive development include:

- Quality and quantity of schooling
- Childhood nutrition
- Prenatal environment
- Lead and other neurotoxins
- Infectious disease burden
- Sleep
- Stress and trauma
- Family resources
- Language exposure and cognitive stimulation
- Poverty and social instability

Severe deprivation can substantially depress cognitive development, and interventions can improve outcomes, especially when they affect early childhood health, education, and stability.

## Bottom line

The evidence shows that human intelligence is **moderately to highly heritable**, especially in adulthood, with genetic differences explaining a substantial share of individual variation in cognitive test scores. But intelligence is also meaningfully shaped by environment, and heritability does not imply immutability or genetic destiny. Both genes and environments matter, and they often interact.


text:
Human intelligence—usually measured as general cognitive ability (“g”) or IQ—is **substantially heritable**, but heritability is **not fixed**, **not destiny**, and **does not imply that group differences are genetic**.

## Short answer

Across modern behavioral genetics studies:

- **Childhood IQ heritability:** roughly **20–40%**
- **Adolescent IQ heritability:** roughly **40–60%**
- **Adult IQ heritability:** often around **50–80%**, with many estimates near **60–70%**
- **Genome-wide DNA studies** currently explain a smaller but growing share, often **~10–20% of variance** depending on sample, measure, and method, while SNP-based heritability estimates are higher.

So the evidence suggests that **genetic differences among individuals contribute importantly to differences in cognitive ability**, especially by adulthood, but **environment also matters a lot**.

---

## What “heritability” means

Heritability is the proportion of variation in a trait **within a specific population, at a specific time, in a specific environment** that is statistically associated with genetic differences.

It does **not** mean:

- “70% of a person’s intelligence is genetic”
- “IQ cannot be changed”
- “environment does not matter”
- “differences between populations are genetic”

For example, height is highly heritable in well-nourished populations, but nutrition can still strongly affect average height.

---

## Main lines of evidence

### 1. Twin studies

Twin studies compare:

- **Identical twins**, who share nearly all their DNA
- **Fraternal twins**, who share about half their segregating DNA

Identical twins tend to be more similar in IQ than fraternal twins. This pattern is found repeatedly across countries and decades.

Typical findings:

- Higher IQ similarity among identical twins
- Higher similarity even when twins are reared apart, though such samples are smaller and have limitations
- Increasing heritability from childhood into adulthood

This is one of the strongest bodies of evidence that genetic factors contribute to individual differences in intelligence.

---

### 2. Adoption studies

Adoption studies examine whether adopted children resemble their biological or adoptive relatives.

Common pattern:

- In early childhood, adopted children’s IQs often resemble both adoptive family environment and biological background.
- By adulthood, resemblance to biological relatives tends to increase, while resemblance to adoptive siblings or adoptive parents often decreases.

This suggests that shared family environment matters more earlier in life, while genetic influences become more apparent over development.

---

### 3. Molecular genetic studies

Genome-wide association studies, or GWAS, scan DNA across hundreds of thousands or millions of people to identify variants associated with cognitive performance or educational attainment.

Findings:

- Intelligence is **highly polygenic**: influenced by thousands of genetic variants, each with tiny effects.
- No single “intelligence gene” exists.
- Polygenic scores can predict some differences in cognitive performance and educational outcomes, but prediction is still limited.
- Many discovered genetic associations may partly reflect indirect social and environmental pathways, such as parental genetics shaping the home environment. This is called **genetic nurture**.

Molecular evidence confirms that DNA differences are associated with intelligence, but it also shows the trait is biologically complex and deeply intertwined with environment.

---

## Why heritability rises with age

One robust finding is that intelligence becomes more heritable from childhood to adulthood.

Possible explanations include:

1. **Gene–environment correlation**
   As people grow older, they increasingly select and shape environments that fit their genetic tendencies. For example, a child with a predisposition toward verbal ability may read more, seek intellectual peers, and choose challenging coursework.

2. **Greater autonomy**
   Adults have more freedom than children to choose jobs, hobbies, social networks, and learning opportunities.

3. **Cumulative developmental feedback**
   Small early differences can compound over time through practice, schooling, encouragement, and opportunity.

This does not mean genes “switch on” and environment disappears. Rather, genetic tendencies and environmental experiences become increasingly correlated.

---

## Environment still matters

Even if IQ is moderately to highly heritable, environmental influences remain important.

Relevant environmental factors include:

- Prenatal health
- Nutrition
- Lead and toxin exposure
- Childhood illness
- Stress and trauma
- Quality of schooling
- Family resources
- Cognitive stimulation
- Sleep
- Social stability
- Discrimination and poverty

The **Flynn effect** is especially important: average IQ scores rose substantially across many countries during the 20th century, too quickly to be explained by genetic evolution. This shows that broad environmental changes can shift population averages.

---

## Heritability can vary by social context

Heritability estimates are not universal constants.

In some studies, especially in the United States, heritability of cognitive ability appears lower among children in more deprived environments, where poverty, poor schooling, stress, and health risks may suppress genetic potential. In more advantaged environments, genetic differences may explain more of the remaining variation.

However, this pattern is not identical in all countries. In societies with stronger social safety nets or more equal access to education and healthcare, the relationship between socioeconomic status and heritability can differ.

---

## Individual differences vs. group differences

This distinction is crucial.

Evidence that intelligence is heritable **within a population** does not tell us why average scores differ between groups, countries, social classes, or historical periods.

For example:

- Height is highly heritable within a well-fed population.
- But average height differences between countries or historical eras can be largely environmental.

Similarly, IQ differences between groups can be affected by schooling, wealth, health, discrimination, test familiarity, language, stress, and many other environmental factors. Heritability estimates alone cannot establish genetic causes for group differences.

---

## Bottom line

The best evidence shows that human intelligence is **substantially heritable**, especially in adulthood, with typical estimates around **50–70%** in many studied populations. This conclusion is supported by twin, adoption, family, and molecular genetic research.

But intelligence is also strongly shaped by environment, development, culture, education, health, and opportunity. Heritability is a population statistic, not a personal fate, and it does not justify conclusions about genetic causes of group differences.


text:
Human intelligence (often measured as IQ or general cognitive ability, “g”) is **substantially heritable**, but heritability is often misunderstood. The best summary is:

- In modern industrialized populations, **genetic differences account for a meaningful share of individual differences in cognitive test performance**.
- Heritability is **not 100%**, and environment still matters a lot.
- Heritability estimates apply to **variation within a studied population at a given time**, not to individuals, not to fixed destiny, and not automatically to differences between populations.

## What “heritability” means

A heritability estimate answers a specific question:

> Of the differences among people in a particular population and environment, what proportion is statistically associated with genetic differences?

So if IQ heritability is estimated at 60%, that does **not** mean “60% of a person’s intelligence is genetic.” It means that, in that population, about 60% of the **variation between people** is associated with genetic variation.

A trait can be highly heritable and still strongly affected by environment. For example, height is highly heritable, but nutrition and disease can shift average height dramatically.

## Typical estimates

Across many studies, estimates roughly look like this:

- **Childhood:** heritability often around **20–40%**
- **Adolescence:** often around **40–60%**
- **Adulthood:** often around **50–80%**

A common broad estimate for adult intelligence in developed countries is around **50–70% heritable**, depending on the sample and methods.

One notable finding is that measured heritability of intelligence tends to **increase with age**. This may happen because people increasingly select, shape, and create environments that fit their genetic tendencies — for example, choosing certain books, hobbies, friends, academic paths, or occupations.

## Main lines of evidence

### 1. Twin studies

Twin studies compare identical twins, who share nearly all their DNA, with fraternal twins, who share about half their segregating DNA.

Findings generally show that:

- Identical twins are more similar in IQ than fraternal twins.
- Identical twins reared apart are still quite similar.
- Similarity often increases from childhood to adulthood.

This is one of the strongest traditional sources of evidence that genes contribute substantially to cognitive differences.

However, twin studies rely on assumptions, such as the “equal environments” assumption: that identical and fraternal twins experience equally similar environments relevant to the trait. Researchers debate these assumptions, but the basic finding of genetic influence is robust.

### 2. Adoption studies

Adoption studies compare children with their biological and adoptive relatives.

The general pattern:

- In childhood, adopted children’s IQ can resemble both adoptive-family environment and biological-family background.
- By adulthood, resemblance to biological relatives often becomes stronger than resemblance to adoptive relatives.
- Adoption into more advantaged environments can raise cognitive outcomes, especially when children come from deprived conditions.

This supports both genetic influence and environmental influence.

### 3. Molecular genetics and GWAS

Genome-wide association studies, or GWAS, scan DNA across very large samples to find genetic variants associated with educational attainment, cognitive performance, or IQ-related measures.

These studies show:

- Intelligence is **highly polygenic**: influenced by thousands of genetic variants, each with tiny effects.
- No single “intelligence gene” exists.
- Polygenic scores can predict some variation in cognitive or educational outcomes, but imperfectly.
- Current polygenic scores explain much less variance than twin-study heritability estimates, though their predictive power has grown with larger samples.

This confirms that genetic influence is real, diffuse, and probabilistic rather than deterministic.

## Environment still matters

Environmental influences on intelligence include:

- Prenatal health
- Nutrition
- Exposure to toxins, such as lead
- Childhood disease burden
- Quality of schooling
- Family stress and stability
- Language exposure
- Cognitive stimulation
- Sleep, safety, and emotional support
- Socioeconomic conditions

Severe deprivation can substantially depress cognitive development, and improved environments can raise outcomes. The **Flynn effect** — the large rise in average IQ scores across many countries during the 20th century — is strong evidence that environmental change can shift population averages.

## Shared vs non-shared environment

Behavioral genetics often separates environmental effects into:

- **Shared environment:** factors that make siblings similar, such as family socioeconomic status or household resources.
- **Non-shared environment:** factors that make siblings different, such as different peer groups, teachers, illnesses, or idiosyncratic experiences.

For IQ:

- Shared family environment tends to matter more in childhood.
- Its measured effect often declines in adulthood.
- Non-shared environment and measurement error account for a significant portion of remaining variation.

This does not mean family environment “doesn’t matter.” It means that, within the studied populations, long-term differences between siblings are not explained as strongly by the measured shared family factors as many people might expect.

## Heritability can vary by context

Heritability is not a universal constant. It can change depending on:

- Age
- Country
- Socioeconomic range
- Educational access
- Nutrition
- Inequality
- Measurement quality

In environments where basic needs are unmet, environmental constraints can suppress genetic potential, lowering heritability. In more equal or resource-rich environments, genetic differences may explain a larger share of remaining variation.

There has been debate about whether IQ heritability is lower among children in low-socioeconomic-status families. Some U.S. studies found this pattern, while some European and other studies found weaker or no effects. The overall point remains: heritability depends on environmental context.

## What the evidence does *not* show

The evidence does not show that intelligence is fixed or unchangeable.

It also does not show that education, parenting, health, or social policy are irrelevant.

And importantly, heritability within a population does **not** explain differences between groups or societies. If one population has higher average test scores than another, that difference could be environmental, genetic, both, or due to measurement and cultural factors. Heritability estimates alone cannot answer that question.

## Bottom line

Human intelligence is **moderately to highly heritable**, especially in adulthood, with many studies suggesting adult heritability around **50–70%** in contemporary developed populations. The evidence comes from twin, adoption, family, and molecular-genetic studies.

But intelligence is also substantially shaped by environment. Genes influence cognitive development through many small effects and through interactions with life experience. Heritability is a population-level statistic, not a measure of inevitability, and high heritability does not mean intelligence cannot be improved or affected by social conditions.


text:
Human intelligence (often measured as IQ or “general cognitive ability,” *g*) is **substantially heritable**, but it is **not genetically fixed** and heritability does **not** mean immutability.

## Short answer

In modern, relatively affluent populations:

- **Childhood:** intelligence is often estimated to be about **30–50% heritable**.
- **Adolescence:** estimates rise to roughly **50–60%**.
- **Adulthood:** estimates are commonly around **60–80%**.

A reasonable summary is: **about half or more of individual differences in adult intelligence within a given population are associated with genetic differences**, with the rest due to environmental influences, developmental factors, measurement error, and gene–environment interplay.

## What “heritability” means

Heritability is a population statistic:

> It is the proportion of variation in a trait, within a particular population and environment, that is statistically associated with genetic variation.

So if adult IQ is “70% heritable,” that does **not** mean 70% of a person’s intelligence is caused by genes. It means that, in that population, 70% of the observed differences between people are associated with genetic differences.

Heritability can change across societies, historical periods, age groups, and environments.

## Main evidence

### 1. Twin studies

Identical twins share ~100% of their segregating DNA; fraternal twins share ~50% on average.

Across many studies:

- **Identical twins** tend to be much more similar in IQ than **fraternal twins**.
- Identical twins reared apart are still substantially similar, though not identical.
- This pattern strongly suggests a genetic contribution.

Typical correlations are roughly:

- Identical twins reared together: high, often around **0.75–0.85**
- Fraternal twins reared together: moderate, often around **0.40–0.60**
- Identical twins reared apart: often around **0.60–0.75**

The exact numbers vary by study, age, and sample.

### 2. Adoption studies

Adoption studies also support genetic influence.

Common findings:

- In early childhood, adopted children’s IQs correlate somewhat with their adoptive family environment.
- As children grow older, their IQs tend to become more similar to their biological relatives and less similar to their adoptive relatives.
- By adulthood, resemblance between adoptive siblings is often small, while resemblance to biological relatives remains stronger.

This suggests that shared family environment matters more in childhood, while genetic influences become more pronounced with age.

### 3. Molecular genetics

Genome-wide association studies, or GWAS, show that intelligence is influenced by **many thousands of genetic variants**, each with very small effects.

Important findings:

- There is no single “intelligence gene.”
- Intelligence is highly **polygenic**.
- Common genetic variants captured by SNP arrays explain a meaningful but incomplete share of variance, often around **20–30%** depending on the measure and sample.
- Polygenic scores can predict some differences in cognitive performance and educational outcomes, but they are far from deterministic and are less accurate across ancestries and social contexts.

This molecular evidence confirms that genetic influence is real, though twin-study heritability estimates are generally larger than what current measured DNA variants can explain.

## Why heritability rises with age

A striking finding is that intelligence becomes more heritable from childhood to adulthood.

Possible reasons include:

1. **Gene–environment correlation:** As people age, they increasingly select, shape, and create environments that fit their dispositions and abilities.
2. **Reduced shared family influence:** The common home environment matters more in childhood than adulthood.
3. **Cumulative developmental effects:** Small genetic tendencies can compound over time through education, interests, peer groups, and practice.

For example, a child with a slight early advantage in verbal ability may read more, receive more encouragement, choose more cognitively demanding activities, and gradually widen the gap.

## Environment still matters greatly

High heritability does not mean environment is unimportant.

Environmental factors that can affect cognitive development include:

- Nutrition
- Prenatal health
- Exposure to toxins such as lead
- Quality of schooling
- Chronic stress
- Sleep
- Disease burden
- Early language exposure
- Family resources
- Social stability
- Access to books, enrichment, and safe learning environments

The **Flynn effect** is especially important: IQ scores rose substantially across many countries during the 20th century, far too quickly to be explained by genetic evolution. This shows that environmental changes can have large effects on population-level cognitive performance.

## Heritability can differ by context

In environments where basic needs are well met, genetic differences may account for more of the remaining variation in intelligence. In more deprived environments, environmental constraints can suppress genetic potential.

Some studies, especially in the United States, have found lower heritability of IQ among children in lower socioeconomic-status families, suggesting that poverty and deprivation can reduce the extent to which genetic differences are expressed. Evidence for this effect is mixed across countries, and it appears weaker in some European samples with stronger social supports.

## What the evidence does not show

The evidence does **not** show that intelligence is fixed at birth.

It also does **not** justify simple genetic explanations for differences between social groups. Heritability within a population does not explain differences between populations or groups. For example, height is highly heritable, but average height can change greatly because of nutrition and health.

Similarly, even if IQ is substantially heritable within a given population, group differences can still be heavily influenced by environment, history, opportunity, discrimination, schooling, health, and socioeconomic conditions.

## Bottom line

The best evidence shows that human intelligence is **moderately to highly heritable**, especially in adulthood, with estimates often around **60–80%** in developed populations. The evidence comes from twin studies, adoption studies, and molecular genetics.

But intelligence is also strongly shaped by environment, development, and social conditions. Heritability describes sources of variation within a particular population; it does not mean intelligence is unchangeable, genetically predetermined, or immune to environmental improvement.


text:
Human intelligence, usually measured with IQ or broader cognitive-test batteries, is **substantially heritable**, but it is **not genetically fixed**. The best short answer is:

> In contemporary, well-nourished populations, genetic differences account for roughly **50% or more** of variation in adult cognitive ability, with estimates often around **50–80%** in adulthood. In childhood the heritability is usually lower, often around **20–50%**, and it tends to increase with age.

“Heritable” here means **variation among individuals within a particular population and environment** that is statistically associated with genetic differences. It does **not** mean that intelligence is unchangeable, that environment is unimportant, or that group differences are genetic.

## Main findings from the evidence

### 1. Twin and adoption studies show substantial genetic influence

The strongest traditional evidence comes from comparing relatives with different degrees of genetic relatedness:

- **Identical twins** share ~100% of their segregating DNA.
- **Fraternal twins/siblings** share ~50% on average.
- **Adopted siblings** usually share a home environment but not genes.

Across many studies:

- Identical twins tend to be much more similar in IQ than fraternal twins.
- Identical twins reared apart are still quite similar, though not identical.
- Adopted children’s IQs resemble their biological parents increasingly with age.
- Shared family environment matters a lot in childhood but tends to decline in influence by adulthood.

This pattern supports a meaningful genetic contribution.

### 2. Heritability rises with age

One of the most replicated findings is that IQ heritability tends to increase from childhood to adulthood.

Approximate ranges often reported:

| Age period | Approximate heritability of cognitive ability |
|---|---:|
| Early childhood | ~20–40% |
| Middle childhood/adolescence | ~40–60% |
| Adulthood | ~50–80% |

Why might heritability increase? One explanation is **gene–environment correlation**: as people age, they increasingly choose, shape, and evoke environments that match their dispositions and abilities. For example, a child inclined toward reading may seek books, advanced classes, or intellectually stimulating peers, amplifying initial differences.

### 3. Shared environment is important early, less so later

“Shared environment” means factors that make siblings raised together more similar: household income, parenting style, neighborhood, schools, etc.

Twin/adoption studies generally find:

- Shared family environment has a **noticeable effect in childhood**.
- Its measured effect on IQ often becomes **smaller in adulthood**.
- Nonshared environment — experiences that make siblings different, plus measurement error — remains important.

This does not mean family or schooling “do not matter.” It means that in many studied populations, the environmental factors that make siblings in the same family similar explain less adult IQ variation than genetic differences do.

### 4. DNA-based studies confirm polygenic influence

Modern genome-wide association studies, or GWAS, show that cognitive ability is influenced by **many thousands of genetic variants**, each with very small effects.

Important points:

- There is no single “intelligence gene.”
- Intelligence is highly **polygenic**.
- SNP-based heritability — the proportion explained by common measured DNA variants — is usually lower than twin-study heritability, often around **20–30%** or somewhat more depending on the trait and method.
- Polygenic scores can predict some variation in educational achievement and cognitive performance, but they are far from deterministic.

For example, current polygenic scores may explain a modest fraction of individual differences, often in the single digits to low teens percentage-wise depending on sample, phenotype, and ancestry. That is scientifically meaningful but not enough to make precise individual predictions.

### 5. Environment clearly matters too

High heritability does not imply immutability. Several lines of evidence show environmental effects:

- **The Flynn effect:** IQ scores rose substantially across much of the 20th century in many countries, too quickly to be caused by genetic evolution.
- **Education:** More schooling is associated with gains in cognitive test performance, and natural-experiment studies suggest schooling can have causal effects.
- **Nutrition, health, toxins, stress, and deprivation** can affect cognitive development.
- **Extreme deprivation** can severely impair cognitive outcomes, while enriched or improved environments can help.

A trait can be highly heritable and still environmentally responsive. Height is a useful analogy: height is highly heritable in well-nourished populations, yet nutrition and disease strongly affect average height.

## What heritability does and does not mean

### Heritability is population-specific

A heritability estimate applies to a particular population living in a particular range of environments. If environments become more equal, heritability can rise because remaining differences are more genetic. If environments become more unequal or deprived, environmental variance can contribute more.

### Heritability within a group does not explain differences between groups

A common mistake is to infer that because intelligence is heritable within a population, differences between populations must be genetic. That does not follow.

For example, plant height may be highly heritable within two fields, but if one field has poor soil and the other has rich soil, the average height difference between fields may be environmental.

### High heritability does not mean fixed destiny

Even if adult IQ heritability is around 60%, that does not mean “60% of a person’s intelligence is genetic.” Heritability is about **variation across people**, not the composition of an individual. It also does not mean interventions cannot work.

## Bottom line

The evidence from twin, adoption, family, and DNA-based studies shows that human intelligence is **substantially heritable**, especially in adulthood. A reasonable summary is:

- **Childhood:** genetic influence is moderate, often around **20–50%**.
- **Adulthood:** genetic influence is higher, commonly around **50–80%**.
- Intelligence is influenced by **many genes of tiny effect**, not a few major genes.
- **Environment remains important**, especially education, health, nutrition, deprivation, and broader social conditions.
- Heritability estimates describe variation **within studied populations**, not inevitability or the causes of group differences.


text:
Human intelligence—usually measured with IQ or broader cognitive-test batteries—is **substantially heritable**, especially by adulthood. The best-supported conclusion is:

> **In contemporary populations with reasonably good nutrition, schooling, and health care, genetic differences account for roughly 50–80% of variation in adult cognitive test performance.**
> In childhood the estimate is lower, often around **20–50%**, and it tends to rise with age.

“Heritable” here means **variation within a population** that is statistically associated with genetic differences. It does **not** mean intelligence is fixed, unchangeable, or unaffected by environment.

## Main evidence

### 1. Twin studies
Twin studies compare identical twins, who share ~100% of their DNA, with fraternal twins, who share ~50% on average.

Typical findings:

- **Identical twins reared together** have very similar IQ scores, often correlations around **0.80–0.90**.
- **Fraternal twins reared together** are less similar, often around **0.50–0.60**.
- **Identical twins reared apart** are still highly similar, often around **0.60–0.75**, though estimates vary and samples are smaller.

This pattern strongly suggests a genetic contribution.

### 2. Adoption studies
Adoption studies separate genetic and family-environment effects.

Common findings:

- In childhood, adopted children’s IQs are influenced by the adoptive home environment.
- As they grow older, their IQs tend to become more similar to their **biological relatives** and less similar to their **adoptive relatives**.
- Shared family environment often matters in childhood but appears to contribute less to IQ differences by adulthood in many modern samples.

### 3. Molecular genetics
Genome-wide association studies show that intelligence is influenced by **many thousands of genetic variants**, each with tiny effects.

Findings include:

- Common genetic variants measured by SNP arrays explain roughly **20–30%** of variation in cognitive ability in many studies.
- Polygenic scores predict some differences in cognitive performance and educational outcomes, but they are far from deterministic and leave most individual variation unexplained.
- The gap between twin-study heritability and SNP-based heritability is partly due to rare variants, imperfect measurement, gene–gene and gene–environment processes, and methodological differences.

## Heritability changes with age

A consistent result is that heritability of intelligence tends to **increase from childhood to adulthood**.

Approximate ranges:

| Age | Estimated heritability of IQ |
|---|---:|
| Early childhood | ~20–40% |
| Middle childhood/adolescence | ~40–60% |
| Adulthood | ~50–80% |

One explanation is **gene–environment correlation**: as people age, they increasingly select, shape, and evoke environments that match their genetically influenced tendencies. For example, a child with strong verbal ability may read more, receive more encouragement, and pursue more cognitively demanding activities.

## Environment still matters a lot

High heritability does not mean environment is unimportant. Intelligence is affected by:

- prenatal environment
- nutrition
- exposure to toxins such as lead
- disease burden
- schooling quality
- stress and deprivation
- sleep
- family stimulation
- socioeconomic conditions

Large environmental effects are obvious historically. For example, IQ scores rose substantially during the 20th century in many countries—the **Flynn effect**—too quickly to be genetic. Improvements in education, nutrition, health, and cognitive demands likely contributed.

Severe deprivation can also depress cognitive development, and interventions can improve outcomes, especially when they affect health, schooling, and early childhood conditions.

## Important caveats

1. **Heritability is population-specific.**
   An estimate like “IQ is 60% heritable” applies to a particular population in a particular environment. It can change if environments become more equal or more unequal.

2. **Heritability does not imply immutability.**
   Height is highly heritable, but average height increased with better nutrition. The same logic applies to cognitive traits.

3. **Heritability within groups does not explain differences between groups.**
   A trait can be highly heritable within a population while between-group differences are caused partly or mostly by environmental factors.

4. **Intelligence is polygenic and probabilistic.**
   There is no single “intelligence gene.” Genetic influence is spread across many variants and interacts with environments.

5. **IQ is useful but incomplete.**
   IQ tests measure important cognitive abilities and predict educational and occupational outcomes, but they do not capture all forms of competence, creativity, wisdom, motivation, or character.

## Bottom line

The evidence from twins, adoption studies, and modern genomics shows that **human intelligence is meaningfully and substantially heritable**, especially in adulthood. A reasonable summary is:

- **Childhood IQ:** moderately heritable, with shared environment playing a larger role.
- **Adult IQ:** highly heritable, often estimated around **50–80%**.
- **Environment:** still crucial, especially for development, deprivation, education, health, and population-level changes.
- **Genes:** influence intelligence through many small effects, not through deterministic “IQ genes.”


text:
Human intelligence, as measured by cognitive tests/IQ and related “general cognitive ability” (often called *g*), is **substantially heritable**, but it is **not genetically determined**. The best evidence suggests that genetic differences account for a meaningful share of individual differences in intelligence within a given population, while environment also matters a lot.

## Short answer

- **Heritability of intelligence is roughly:**
  - **~20–40% in early childhood**
  - **~40–60% in adolescence**
  - **~50–80% in adulthood**, depending on the population and methods
- Intelligence is **highly polygenic**: thousands of genetic variants each have tiny effects.
- Heritability does **not** mean immutability. Education, nutrition, disease burden, family environment, stress, toxins, and social conditions can affect cognitive development.
- Heritability estimates apply to **variation among individuals within a studied population**, not to differences between populations or to an individual’s “percentage genetic” intelligence.

## What “heritability” means

Heritability is the proportion of variation in a trait within a population that is statistically associated with genetic differences among individuals.

So if adult IQ has a heritability of 60% in a certain population, that means about 60% of the differences between people in that population are associated with genetic differences. It does **not** mean:

- 60% of a person’s intelligence is genetic;
- environment is unimportant;
- intelligence cannot be changed;
- group differences are genetic.

Heritability can change depending on the environment. For example, if nutrition, schooling, and health care are relatively equal, genetic differences may explain more of the remaining variation. In harsher or more unequal environments, environmental deprivation can suppress genetic potential and lower heritability estimates.

## Main lines of evidence

### 1. Twin studies

Twin studies compare identical twins, who share nearly 100% of their DNA, with fraternal twins, who share about 50% on average.

A common finding is that identical twins are more similar in IQ than fraternal twins. This pattern is strong evidence that genetics contributes to cognitive differences.

Typical correlations are roughly:

- Identical twins raised together: high similarity, often around **0.75–0.85**
- Fraternal twins raised together: lower similarity, often around **0.45–0.60**
- Identical twins raised apart: still substantially similar, often around **0.65–0.75**, though these studies are rarer and have limitations

These findings imply a significant genetic contribution.

### 2. Adoption studies

Adoption studies compare children with their biological and adoptive relatives.

The general pattern is:

- In childhood, adopted children’s IQs are influenced by the adoptive home environment.
- As children grow older, their IQs tend to resemble their biological relatives more strongly.
- The influence of shared family environment often appears to decline by adulthood, though this does not mean families or schooling are unimportant.

This supports the idea that genetic influences on intelligence become more visible with age.

### 3. Molecular genetic evidence

Modern genome-wide association studies, or GWAS, have found many genetic variants associated with cognitive ability and educational attainment.

Important points:

- No single “intelligence gene” exists.
- The effects of individual variants are tiny.
- Polygenic scores can predict some variation in educational attainment and cognitive performance, but they are far from deterministic.
- SNP-based heritability estimates — heritability captured by common measured genetic variants — are often lower than twin-study estimates, commonly around **20–30%** for cognitive traits, because they miss rare variants, structural variants, gene–environment effects, and other sources of genetic influence.

The molecular evidence confirms that intelligence is genetically influenced and highly polygenic.

## Heritability increases with age

One of the most consistent findings is that the heritability of intelligence tends to rise from childhood to adulthood.

Possible reasons include:

- Children gradually select and shape environments that fit their genetic tendencies.
- Educational and social choices amplify small genetic differences.
- Cognitive abilities stabilize with development.
- Shared family environment becomes less dominant as people become independent.

This is known as **gene–environment correlation**: genetic tendencies can influence the environments people experience. For example, a child with a strong interest in reading may seek out books, receive encouragement, and develop verbal skills further.

## Environment still matters

High heritability does not mean environment is weak. Environmental factors known to affect cognitive development include:

- prenatal health;
- maternal stress and substance exposure;
- childhood nutrition;
- lead and other toxins;
- infectious disease burden;
- sleep;
- quality of schooling;
- family stability and stress;
- poverty;
- access to books, language, and cognitive stimulation.

The **Flynn effect** — the large rise in IQ scores across many countries during the 20th century — is especially important evidence that environmental changes can substantially affect test performance over generations. Genes did not change quickly enough to explain those gains.

## Shared vs non-shared environment

Behavioral genetic studies often divide environmental effects into:

- **Shared environment**: factors that make siblings similar, such as family socioeconomic status, parenting style, neighborhood, and schools.
- **Non-shared environment**: factors that make siblings different, such as different peer groups, illnesses, accidents, teacher relationships, measurement error, and unique experiences.

For intelligence:

- Shared environment tends to matter more in childhood.
- Its measured effect often declines in adulthood in affluent populations.
- Non-shared environment and measurement error account for a significant portion of variation at all ages.

## Socioeconomic context matters

Some studies suggest that heritability of intelligence may be lower in disadvantaged environments, especially in childhood. In such contexts, environmental constraints may prevent children from reaching their cognitive potential. However, findings vary by country and sample.

Broadly: in societies with less deprivation and more equal access to schooling, genetic differences may account for more variation. In societies with greater deprivation, environmental differences may account for more.

## What the evidence does not show

The evidence does **not** show that:

- intelligence is fixed at birth;
- education cannot improve cognitive outcomes;
- social interventions are useless;
- group differences are genetic;
- individual potential can be accurately predicted from DNA.

Heritability is about statistical variation in a particular population under particular environmental conditions. It cannot be casually generalized to historical, ethnic, racial, or national group differences.

## Bottom line

Human intelligence is **moderately to highly heritable**, especially in adulthood, with estimates often around **50–80%** in developed-country adult samples. The evidence comes from twin, adoption, family, and molecular genetic studies. But intelligence is also shaped by environment, development, schooling, health, and social conditions. The genetic influence is real, highly polygenic, and probabilistic — not deterministic.


text:
Human intelligence, usually measured as **general cognitive ability (“g”) or IQ**, is **moderately to highly heritable**, but heritability is often misunderstood.

## Short answer

Across modern behavioral-genetic studies, the heritability of intelligence is roughly:

- **Childhood:** ~20–40%
- **Adolescence:** ~40–60%
- **Adulthood:** ~50–80%

A common summary is that **about half or more of the variation in adult intelligence within a given population is associated with genetic differences**, with the rest due to environmental factors, measurement error, developmental randomness, and gene–environment interplay.

But this does **not** mean intelligence is “fixed,” “genetically determined,” or unaffected by environment.

---

## What “heritability” means

Heritability is the proportion of **variation among individuals in a particular population at a particular time** that is statistically associated with genetic differences.

It does **not** mean:

- “X% of a person’s intelligence is genetic”
- “Intelligence cannot be changed”
- “Group differences are genetic”
- “Genes matter independently of environment”

For example, height is highly heritable, but average height can increase substantially across generations due to better nutrition and health.

The same logic applies to intelligence.

---

## Main lines of evidence

### 1. Twin studies

Twin studies compare identical twins, who share nearly all their DNA, with fraternal twins, who share about half of their segregating genetic variation.

A consistent finding is:

- Identical twins are more similar in IQ than fraternal twins.
- Identical twins raised apart are still substantially similar.
- The genetic contribution tends to increase with age.

This supports a substantial genetic influence on cognitive ability.

However, twin studies rely on assumptions, such as how similar the environments of identical and fraternal twins are. Modern analyses try to test or adjust for these issues, but they remain part of the interpretation.

---

### 2. Adoption studies

Adoption studies show that adopted children’s cognitive scores are often influenced by their adoptive environments, especially in childhood.

But as children grow up, their IQs tend to become more similar to those of their biological relatives than to their adoptive relatives.

This pattern supports both conclusions:

- Environment matters, especially early in life.
- Genetic influences become more apparent with age.

---

### 3. DNA-based studies

Genome-wide association studies show that intelligence is **highly polygenic**: influenced by thousands of genetic variants, each with tiny effects.

DNA-based estimates, such as SNP heritability, often find that common measured genetic variants account for roughly **20–30%** of variation in cognitive ability, sometimes more depending on the measure and sample.

Polygenic scores can predict some variation in cognitive outcomes, but currently they explain only a minority of variance, often roughly in the single digits to low teens depending on trait, sample, and ancestry.

DNA evidence confirms that genetic differences are involved, but also shows there is no single “intelligence gene.”

---

## Why heritability increases with age

One of the more interesting findings is that the heritability of intelligence often rises from childhood into adulthood.

Possible reasons include:

1. **Greater autonomy with age**
   As people grow up, they select environments that fit their interests and abilities.

2. **Gene–environment correlation**
   A child with a genetic tendency toward verbal ability may read more, receive more encouragement, and choose more intellectually demanding activities.

3. **Reduced shared family environmental influence**
   Siblings raised in the same home can become less similar over time as they develop different peer groups, interests, schools, and life paths.

So genes may influence not only cognitive traits directly, but also the environments people seek and create.

---

## Environmental effects are real and important

High heritability does not imply low environmental importance.

Evidence shows that cognitive development can be affected by:

- Schooling quality and duration
- Nutrition
- Prenatal environment
- Childhood disease burden
- Lead and pollution exposure
- Stress and deprivation
- Poverty
- Sleep
- Parenting and language exposure
- Access to books, enrichment, and stable learning environments

Large environmental changes can shift population averages. The **Flynn effect**, the substantial rise in IQ scores across many countries during the 20th century, is strong evidence that environments can meaningfully affect measured cognitive performance.

---

## Heritability varies by population and context

Heritability estimates are not universal constants.

They can change depending on:

- Socioeconomic conditions
- Educational access
- Health and nutrition
- Age
- The range of environments in the sample
- Measurement quality
- Cultural and historical context

In some studies, particularly in the United States, heritability of IQ appears lower among children from low-SES backgrounds, possibly because environmental constraints suppress genetic potential. In other countries, especially those with stronger social supports, this SES moderation is less consistently found.

---

## What the evidence does not show

The evidence does **not** show that:

- Intelligence is determined entirely by genes.
- Environmental interventions are futile.
- Individual potential can be read from DNA.
- Differences between social, ethnic, racial, or national groups are genetic.

Heritability within a population does not explain differences between populations. A trait can be highly heritable within groups while group differences are caused largely or entirely by environment.

---

## Bottom line

The best evidence suggests that **human intelligence is substantially heritable**, especially in adulthood, with estimates often around **50–80%** in well-studied populations. The evidence comes from twin, adoption, family, and DNA-based studies.

But intelligence is also strongly shaped by environment, development, education, health, and social conditions. Heritability describes variation within a given population; it does not mean intelligence is fixed, unchangeable, or reducible to genes.