How can we disentangle nature and nurture? (S1EP17)

Summary

In this insightful discussion, the speaker explores the role of genetics in shaping human behavior, drawing on the 'three laws of behavioral genetics'. The first law asserts that all behavioral traits are partly heritable, with genetic differences contributing to individual variations. The second law reveals that genetic effects often surpass familial ones, challenging the notion that family environment is the primary influence on development. The third law introduces the concept of non-shared environment, emphasizing the significant role of chance and unpredictable factors in personal development. This talk sheds light on the complex interplay between nature and nurture in defining who we are.

Takeaways

• 🧬 All behavioral traits are partly heritable, meaning genetic differences contribute to the variations among individuals within a culture.
• 👥 Identical twins, even when raised apart, show remarkable similarities, suggesting a strong genetic influence on behavior and personality.
• 🏠 The impact of family environment on personality and intelligence is often surprisingly small or even zero, especially when comparing identical twins raised in different families.
• 🌱 The effects of genes are generally stronger than those of family environments, challenging the common belief that parenting styles heavily shape children's outcomes.
• 🧐 There is a significant amount of variation in human behavior that is neither genetic nor familial, indicating other factors beyond genes and family influence.
• 🤔 The concept of 'chance' plays a significant role in personal development, encompassing unpredictable and immeasurable factors that contribute to individual differences.
• 🧪 Advances in DNA analysis allow for the observation of statistical correlations between genetic variants and behavioral traits, reinforcing the idea of genetic influence.
• 👭 Comparisons between identical and fraternal twins provide a powerful method for understanding the role of genetics in behavior.
• 🌟 Judith Harris, a psychologist, highlighted the importance of considering genetic overlap to avoid misattributing parenting effects as heritability.
• 🌐 Cultural differences do matter, as seen in comparisons between vastly different societies, but within the same culture, genetic differences play a more significant role than cultural upbringing.

Q & A

What is the main argument presented in the script about human traits?

The script argues that human traits are a result of evolution and are partly heritable, meaning that genetic differences contribute to the variations we see among individuals.

How does the script suggest that our genetic makeup interacts with our experiences?

The script suggests that our genetic makeup interacts with our experiences to shape who we are, but it also emphasizes that the genetic effects are often stronger than the effects of our family environment.

What are the 'three laws of behavioral genetics' mentioned in the script?

The three laws mentioned are: 1) All behavioral traits are partly heritable. 2) The effects of genes are stronger than the effects of families. 3) There is a lot of variation that is neither genetic nor familial, suggesting a significant role of chance in development.

How does the script explain the heritability of behavioral traits?

The script explains heritability by discussing studies comparing identical twins who share all their genes with fraternal twins who share half their genes, as well as studies on identical twins separated at birth and raised in different environments.

What role does the script suggest that family environment plays in shaping our personalities and behaviors?

The script suggests that the effects of family environment are often surprisingly small or even zero, especially by the time individuals reach adulthood, compared to the impact of genetic factors.

Why does the script find the impact of family environment on development surprising?

The script finds it surprising because people often attribute differences in children's outcomes to parenting styles and family dynamics, but research in behavioral genetics indicates that these factors have less impact than previously thought.

What is Judith Harris's contribution to the understanding of behavioral genetics discussed in the script?

Judith Harris is credited with highlighting the robust findings from behavioral genetics that were often ignored, particularly the idea that genes matter more than family environment in shaping an individual's development.

How does the script address the misconception that environment and heredity are inversely related?

The script clarifies that environment and heredity are not inversely related in the way people often assume. It argues that there is a significant amount of variation that is neither genetic nor familial, indicating that other factors beyond genes and family environment play a role.

What does the script suggest about the role of chance in our development?

The script suggests that chance plays a significant role in our development, including random events such as mutations, brain development variations, and unpredictable life experiences that contribute to making us who we are.

Why does the script consider the findings from behavioral genetics to be counter-intuitive?

The script considers the findings counter-intuitive because they challenge common beliefs about the importance of family environment and parenting in shaping individuals, instead highlighting the strong influence of genetics and the role of chance.

Outlines

00:00

🧬 Genetics and Behavioral Traits

The paragraph discusses the impact of genetics on human behavior and traits. It highlights that talents and temperaments are a result of evolution and are coded in our DNA. The author introduces the concept of behavioral genetics and the 'three laws' that govern it. The first law states that all behavioral traits are partly heritable, meaning genetic differences contribute to the variation among individuals within a culture. The author explains this through the comparison of identical and fraternal twins, as well as identical twins separated at birth and raised in different environments, showing that genetics play a significant role in shaping who we are.

05:00

👨‍👩‍👧‍👦 The Surprising Minimal Impact of Family

This paragraph explores the second law of behavioral genetics, which suggests that the effects of genes are stronger than those of family environments. The author challenges the common belief that family upbringing has a lasting impact on a person's intellect and personality. By examining the cases of identical twins raised in different families and adoptive children, the author illustrates that shared genes have a more significant influence than shared family experiences. The author also critiques the assumption that parenting practices directly shape children's outcomes, arguing that genetic predispositions might be mistakenly attributed to environmental factors.

10:00

🌟 The Role of Chance in Personal Development

The final paragraph delves into the third law of behavioral genetics, which posits that a significant amount of variation in behavior and traits is neither genetic nor familial. The author discusses the difficulty in quantifying the impact of 'chance' on personal development, which includes unpredictable events and factors beyond genetics and family environment. Examples include mutations, random developmental events, and unique life experiences. The author emphasizes the importance of acknowledging the role of chance in shaping individual differences, suggesting that it is a critical factor in understanding human diversity.

Keywords

💡Evolution

Evolution refers to the process by which species of organisms change over time through genetic variation and natural selection. In the context of the video, the speaker suggests that talents and temperaments are results of evolution, implying that certain behavioral traits have developed and persisted because they offered survival or reproductive advantages.

💡Genome

The genome is an organism's complete set of genetic information, encoded in DNA. The video discusses how the genome contains the information that influences who we are, suggesting that our genetic makeup plays a significant role in our development and individual differences.

💡DNA

DNA, or deoxyribonucleic acid, is the molecule that carries genetic instructions for the development, functioning, and reproduction of all known living organisms and many viruses. The script mentions DNA as the medium through which genetic information is coded and inherited, affecting our traits and behaviors.

💡Heritability

Heritability is the degree to which variations in traits or characteristics within a population can be attributed to genetic differences between individuals. The video emphasizes that all behavioral traits are partly heritable, meaning that genetic differences contribute to the variation we see among individuals.

💡Identical Twins

Identical twins result from a single fertilized egg that splits into two embryos, leading to two individuals with the same genetic material. The video uses identical twins, especially those separated at birth and raised in different environments, to illustrate the strong influence of genetics over environmental factors in shaping personality and behavior.

💡Fraternal Twins

Fraternal twins develop from two separate eggs fertilized by two separate sperm, resulting in siblings who share about 50% of their genes, just like any other siblings. The script contrasts fraternal twins with identical twins to demonstrate genetic influence on behavior, as identical twins are more similar despite potentially different upbringings.

💡Behavioral Genetics

Behavioral genetics is the field of science that studies how genetic and environmental factors interact to produce individual differences in behavior. The video discusses several 'laws' of behavioral genetics, highlighting the importance of genetics in determining behavior and personality traits.

💡Environment

In the context of the video, environment refers to all external factors that can influence an individual's development, such as family, culture, and social interactions. The speaker argues that while the environment plays a role, its impact on behavioral traits is often less significant than genetic factors.

💡Judith Harris

Judith Harris is a psychologist mentioned in the video who contributed significantly to the understanding of how genes and environment interact to shape behavior. Her insights challenge traditional views on the primacy of family influence and emphasize the importance of genetics and chance events.

💡Chance

Chance, as discussed in the video, refers to random events or variations that cannot be predicted or measured and that may have significant impacts on individual development. The speaker suggests that chance events, such as mutations or random developmental factors, contribute to the uniqueness of individuals, even among identical twins.

💡The Blank Slate

The term 'The Blank Slate' refers to the book by Steven Pinker, from which the script is taken. The book challenges the idea that human beings are born with a mind devoid of any personality or predispositions and that all behaviors are solely the product of experience and socialization. The video script delves into the themes of the book, particularly the role of genetics in human behavior.

Highlights

Talents and temperaments are a result of evolution, influencing brain development and genetic makeup.

Genetic endowment interacts with experience to shape individual differences.

The majority of human genes are shared, contributing to our unity as a species.

Differences among individuals are partly due to genetic variations.

Modern DNA analysis reveals correlations between genetic variants and behavioral traits.

Behavioral genetics findings are replicable and almost law-like.

First law: All behavioral traits are partly heritable.

Second law: Genetic effects are stronger than family environmental effects.

Third law: There's significant variation that is neither genetic nor familial.

Identical twins studies show genetic overlap's role in personality and behavior.

Separated identical twins raised in different families remain remarkably similar.

Family environment has surprisingly little lasting impact on adult personality and intellect.

Cultural differences are significant, but within-culture family effects are minimal.

Parenting effects may be confounded by genetic inheritance.

Judith Harris' insights challenge traditional views on the impact of family and environment.

Chance events, such as mutations and random developmental factors, contribute to individual differences.

The role of chance in development is significant and often unpredictable.

Behavioral genetics findings are counter-intuitive but robust.

The 'three laws' of behavioral genetics offer a new perspective on human development.

Transcripts

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[Music]

with certain talents and temperaments

that they're a result of evolution just

like our our bodies then there's got to

be a way in which they play themselves

out in the development of the brain and

of course that information is coded in

our on our genome in our DNA

a key question is how does our genetic

make up our endowment interact with our

experience to make us who we are in

particular to make us what makes us

different from one another

there are things in our genome that we

all share the vast majority of our genes

are the same as every other human and

that's what's responsible for our Unity

as a species but of course we're not

clones people are different and one can

ask how do we get different

the chapter on children on the

development of children in my book the

blank slate was probably the most

controversial of the 23 chapters even

though there were plenty of hot buttons

in that book such as politics and

violence and sex differences and

discussions of rape and murder and War

and liberal versus conservative

ideologies there's a chapter of children

that that really got people uh hot and

bothered and it came from reporting what

I've come to be known somewhat

informally as the three laws of

behavioral genetics now psychology

doesn't have laws the way physics has

laws but there are findings that are so

replicable over so many studies of

hundreds of thousands of people that

they almost deserve to be called laws

the first law is that all behavioral

traits are partly heritable

what does that mean it means that some

of the variation within a culture

between one person and another what

makes Jason different from Sam what

makes Emily different from Jessica comes

from differences in their genes

how do we know that well nowadays we can

have people drool into tubes and look at

their DNA and we find that there are

massive statistical correlations between

our thousands of genetic variants and

any trait that we try to measure but way

before there were there was that

technology still really in its infancy

there were powerful but simpler methods

of establishing the effect of genes for

example you could compare identical

twins who share all of their genes and

their environment with fraternal twins

who share half their genes and their

environment if the identical twins are

more similar to each other than the

fraternal twins it suggests that their

greater amount of genetic overlap has a

role and there are many complications

and asterisks and digressions that have

been worked out over the decades but the

finding is pretty solid or for that

matter you could look at the special

case of identical twins who are

separated in birth and raised in

different families sometimes different

continents and finding is that they are

remarkably similar not indistinguishable

but but more similar than uh to people

who even grew up in the same family

so the first law is that all traits are

partly not completely but partly

heritable

second law of behavioral genetics turns

up in study after study whatever you

choose to measure whether it's

personality character intelligence

habits smoking drug addiction a number

of books that you read number amount of

Television that you watch likelihood of

getting into trouble with the law that

the effects of the genes are stronger

than effects of families and in fact

often the effects of families are

surprisingly small indeed Zero by the

time you're an adult now this people

find mind-boggling but here's the

rationale behind it remember those

identical twins that were separated at

Birth and brought up in separate

families and you know they're pretty

similar because they have the same genes

even though they were brought up in

different families okay well now compare

them to identical twins that were

brought up in the same family now you

might think wow well they should be

really similar because not only do they

share the

but they also share the same parents the

same neighborhood the same older

siblings the same younger siblings so

they should be much more similar and the

answer is they're not in fact in general

adopted kids who grow up in the same

home are no more similar by the time

they're adults that adopted kids who are

who grow up in separate homes all those

years of growing up with with those

parents leave surprisingly little

lasting stamp on your intellect and

personality now by the way this is not

to say that your culture doesn't matter

culture does matter as we see in

comparing say you know manhattanites

with indigenous people in the Amazon

rainforest or Papua New Guinea or

Bedouins culture obviously matters a lot

but if you were to switch the kids

around in different families within the

same culture you find that there's

surprisingly little effect

hate to interrupt wouldn't you prefer

uninterrupted Indulgence head to find

qualia.com to access the entire series

by The Genius Stephen Pinker completely

ad-free

now people find this mind-boggling

because they look at parents and they

look at kids they see the obvious uh

connection between how the parent

treated the kid and how the kid turned

out and they say well parenting

obviously shaped them but the problem is

that unless you're looking at adoptive

children and their parents you have a

massive confound namely the parents give

their children an environment parents

also give children their genes unless

you have adopted families you can't

tease them apart and when you do tease

them apart with adoptive households you

see that genes matter much more than

families so the fact that parents who

talk more to their kids have kids who

end up with better language skills the

fact that people who spank their kids

end up with kids who are more violent

doesn't necessarily mean that talking to

your kids makes them better at language

it might just mean that people who talk

more have genes that make them more

linguistic and they pass those kids

those genes on to their kids people who

are violent to their kids are more

temperamentally violent that can

inherent that temperament they're more

violent too this is a massive problem in

a lot of social science research where

if you don't take into account the

genetic overlap you can misattribute

effects of heritability and falsely

think that their effects of parenting

this by the way is an Insight that comes

from a psychologist named Judith Harris

she never had a university job because

she was kicked out of graduate school

for not fitting The Stereotype of a

psychologist she ended up turning the

field on its ear by calling attention to

these very robust findings from

behavioral genetics that people tended

to ignore

now the first law is that all behavioral

traits are heritable second law is that

effects of genes are stronger than

effects of families which are often weak

to zero the third law is there's a lot

of variation that is neither genetic nor

familial now people have a lot of

trouble wrapping their heads around this

because everyone thinks oh well there's

heredity there's environment the more

heredity the less environment and vice

versa but actually that turns out not

not to really be true at least if you

consider the environment to be something

that you could really look at or measure

like the effects of families here's the

findings really not all that complicated

let's go back to our identical twins who

are reared together in the same

household

okay they got the same DNA genes are the

same same mother same father same older

siblings and younger siblings same

number of books in the house same number

of TDS in the house same teachers same

same everything so they should be

absolutely indistinguishable they should

be you know clones well if you know a

pair of identical twins you know they're

not indistinguishable they have separate

personalities I know this intimately

having two identical twin uncles Barry

and Mark who are more similar Than

People picked off the street at random

but no one in the family had any doubt

which was which they each had their

personality and that's true of all

individuals

that leads to a real puzzle that I think

psychologists have not really

thought through enough which is

how can they be different

it's not their genes it's not their

environment at least not anything stable

about the environment like who your

mother is or what what neighborhood you

live in

suggests to me that there is a massive

effect of chance on the development of

Who We Are

what do I mean by chance well chance all

kind of Embraces everything that uh that

we can't predict and measure it could be

chance events in the genome new

mutations happen with every baby and

when you have even identical twins who

come from an egg splitting into two

there could be a mutation that develops

in one fertilized egg and embryo but not

in the other there are mutations that

develop as in our bodies as we grow and

develop that could be different in the

two twins there could be factors in

brain development that the genes can't

control down to the last synapse it

could be that growing axons in the brain

of one twin Zig on in one day and they

zag and the other that could be random

factors in development that you don't

take into account when you just look at

families like you know who got the top

of the bed who got the bottom bunk bed

did one child get chased by a dog one

day and the other one not or get teased

by his friends or picked on by a bully

all of these things seem to add up to

make us who we are in a way that we

could never really pin down in our own

autobiographies that we could never pin

down in most scientific studies but may

have a huge effect in uh in who we are

these are the three counter-intuitive

findings from behavioral genetics again

massively replicable that I tried to

explain in the children's chapter of the

blank slate with full credit to Judith

Rich Harris that I consider to be among

the most interesting things I've

discovered about the mystery of Who We

Are