Robert Plomin02 August 2021

How Do Genes Influence Our Behaviour? - Robert Plomin - #353

0Frameworks

10Insights

Insights & moments

The myth-busts, hot takes, explainers, and tools worth keeping.

Myth Buster· 2

Myth Buster08:30

Genes Are Not Destiny: The Myth of Genetic Determinism

While genes strongly influence traits, they do not determine them in a fixed way. Most psychological and behavioral traits are influenced by thousands of tiny genetic differences, creating probabilistic tendencies rather than fixed outcomes. This means people can still change their behavior, even with strong genetic predispositions.

Genetic influence is probabilistic, not deterministic, especially for complex traits.
Unlike single-gene disorders (e.g., Huntington’s), behavioral traits involve thousands of genes with small effects.
You can modify outcomes—e.g., someone with a genetic risk for alcoholism won’t become alcoholic without drinking.
Understanding genetic risk can be motivating, not fatalistic.

“It's not deterministic and that's the way people learned about genetics... but when we get to psychological disorders... they're due to thousands of tiny DNA…”
Robert Plomin · 09:30

#genetics#free will#alcoholism#behavior

Myth Buster79:00

Why School Quality Matters Less Than You Think

Despite parents paying premiums to live in better school districts, school quality explains only 1% of GCSE score variance after controlling for socioeconomic status. Genetic differences between students are far more predictive of academic outcomes than which school they attend.

Ofsted school ratings explain only 4% of variance in student outcomes, dropping to 1% after adjusting for SES.
DNA alone predicts 15% of variance in GCSE scores—more than school quality.
Private schools show no added value; their success comes from selecting high-achieving students.
This suggests that educational policy should focus on individual differences, not school rankings.

“With DNA alone we can explain 15% of the variance of GCSE scores. So it's probably what that's about is that... most schools are pretty…”
Robert Plomin · 80:45

#education#schools#gcse#genetics

Hot Take· 1

Hot Take32:30

There Are No Mental Disorders—Just Dimensions of Genetic Risk

Robert Plomin argues that conditions like dyslexia or schizophrenia aren't categorical disorders but points on a continuum of genetic risk. Thousands of DNA differences contribute small effects, meaning everyone has some level of susceptibility—it's just a matter of degree.

Psychiatric conditions are not 'all-or-nothing' but exist on a spectrum.
Genetic risk is normally distributed—some people have more risk variants by chance.
Labeling someone 'dyslexic' medicalizes what is often just a quantitative difference in reading ability.
This view undermines the traditional medical model and supports a dimensional understanding of mental health.

“There are no disorders. There are just quantitative dimensions.”
Robert Plomin · 33:00

#mental health#schizophrenia#dyslexia#genetics

Explainer· 5

Explainer01:30

Why DNA Matters More Than Anything Else in Shaping Who We Are

Behavioral genetics reveals that inherited DNA differences account for about 50% of the variation in psychological traits, making genetics the largest systematic influence on individual differences in behavior. This doesn't mean environment is irrelevant, but it shows that DNA plays a more dominant role than previously believed.

About half of individual differences in psychological traits are due to inherited DNA differences.
Genes influence traits like IQ, personality, and mental health, not through deterministic pathways, but via probabilistic propensities.
The environment still matters, but its effects are often non-shared and idiosyncratic rather than systematic.
This challenges the long-held belief that upbringing and family environment are the primary shapers of personality and behavior.

“DNA isn't all that matters but it matters more than anything else and it matters more than everything else put together in determining who we…”
Robert Plomin · 10:10

#behavioral genetics#dna#heritability#psychology

Explainer07:30

Why Body Weight Is 70% Heritable

Contrary to popular belief, body weight and BMI are highly heritable—about 70%—meaning most of the variation between people in weight comes from genetic differences. This doesn't mean environment is irrelevant, but that genetic predispositions strongly influence how easily someone gains or loses weight.

Body mass index (BMI) is about 70% heritable across populations.
Genetic influence affects not just metabolism, but psychological traits like satiety, food cue responsiveness, and eating behaviors.
People with high genetic risk for obesity may struggle more despite effort, suggesting the need for greater societal empathy.
Heritability describes population differences, not individual determinism—environment still plays a role.

“Of the differences you see between people in weight, about 70% are due to inherited DNA differences.”
Robert Plomin · 07:50

#genetics#obesity#bmi#heritability

Explainer06:45

Why Growing Up Together Doesn't Make Siblings Alike

Adoptive siblings who grow up in the same home and share the same parents and environment show zero correlation in IQ, proving that shared family environment has little effect on making children similar. Instead, genetics and non-shared, idiosyncratic experiences shape who they become.

Adoptive siblings correlate at zero for IQ, despite identical upbringing.
The shared family environment has minimal impact on psychological traits like intelligence and personality.
Differences between siblings are driven more by genetics and unique life experiences.
This challenges the assumption that parenting style is the main driver of child outcomes.

“How much do these adoptive sibs correlate because they grow up in the same family? They have the same parents. Zero.”
Robert Plomin · 06:45

#parenting#iq#adoption#environment

Explainer38:30

Why IQ Becomes More Heritable as We Age

IQ starts at about 20% heritability in infancy but increases to 60–80% in adulthood. This happens because people increasingly select, modify, and create environments that match their genetic propensities—a process called gene-environment correlation.

Heritability of IQ increases from 20% in infancy to over 60% in adulthood.
As people age, they actively seek out environments that align with their genetic tendencies.
Smart kids ask more questions, read more, and get more out of school, amplifying small initial differences.
This 'snowballing' effect explains why intellectual differences grow over time.

“The heritability of IQ increases linearly throughout the lifespan: 20% in infancy, 40% in childhood, 60% in young adulthood, even 80% later in life.”
Robert Plomin · 39:00

#iq#genetics#development#education

Explainer65:00

The Role of Chance in Shaping Who We Become

After genetics, the most important environmental influences are non-shared and stochastic—random, unique events like a chance encounter or a humiliating moment in school. These idiosyncratic experiences are hard to measure but can have outsized effects on life trajectories.

The environment matters, but not in the way most people think.
Shared family environment has little effect; differences come from unique experiences.
Chance events—like meeting JFK—can redirect a life path.
This 'gloomy prospect' is actually liberating—it shifts focus from control to acceptance.

“The role of chance... of the important environmental factors are sort of idiosyncratic. We call it stochastic chance events.”
Robert Plomin · 65:45

#environment#chance#life events#psychology

Tool· 1

Tool83:30

DNA Dating: The Future of Finding Love?

DNA dating services are emerging, using genetic data to match people based on compatibility. While still in early stages, whole-genome sequencing could one day help couples avoid passing on rare but serious single-gene disorders to their children.

Over 20 companies now offer DNA-based dating services.
George Church’s project offers whole-genome sequencing to assess recessive disease risk in couples.
Ashkenazi Jews have nearly eliminated Tay-Sachs through genetic screening.
This could become routine, like STD testing, without needing new laws.

“If you send your DNA... he will do whole genome sequencing... to determine the extent to which you and your prospective partner have the same…”
Robert Plomin · 85:00

#dna#dating#genetics#reproduction

Takeaway· 1

Takeaway70:00

Parents Matter, But They Don’t Make a Difference

Parents shape their children’s lives through love and support, but they have far less influence on psychological outcomes than genetics. The idea that parenting style determines a child’s success is largely a myth—genetic propensities and chance life events play much larger roles.

Parents don’t make children similar, even when they raise them the same way.
Genetic differences explain more variation than parenting practices.
Parents should focus on understanding their child’s unique interests and aptitudes rather than trying to mold them.
This view is liberating—it reduces guilt and encourages acceptance.

“Parents matter, but they don't make a difference.”
Robert Plomin · 70:00

#parenting#genetics#child development#psychology