behavioural genetics (sapolsky human behavioural biology)

Question 1

What are the major approaches used by the behavioral geneticists? What are the criticisms of these approaches?

Answer 1

Remember they’re all about teasing apart genetic and various environmental influences.
􏰀 Universality, shared among family, and shared as a function of relatedness.
a. Saying traits more shared with closer relatives must be due to the more shared genetics.
b. Criticism: Genetics and environment tend to correlate well within families as a function of
relatedness
c. Criticism: you’re not actually controlling for environment because your pre-natal maternal
environment is crucial (Dutch Hunger Winter, epigenetics, etc.)
􏰀 MZ vs. DZ twins.
a. Criticism: even among MZ twins you have
i. Splitting before day 4􏰂two separate placentas (dichorionic) and two amniotic sacs
ii. Splitting between day 4-7􏰂one placenta (monochorionic) but two amniotic sacs
iii. Splitting after day 7􏰂one placenta and one amniotic sac
b. Criticism: MZ twins are also treated more similarly than DZ twins
􏰀 Adoption studies. Saying that traits more shared with closer relatives must be due to more shared genetics
because the environment is random and not shared.
a. b. c.
Cross-fostering in animals
With MZ twins separated at birth
Compare MZ and DZ twins separated at birth
i. Criticism: adoptees are placed non-randomly
ii. Criticism: you’re going to have pretty small sample size with these very unique cases
iii. Criticism: again, environment starts at conception, not at birth 􏰀 Behavior in the absence of environmental influence
a. Social smiling in congenitally blind babies and babbling in congenitally deaf babies
b. Lab rats 100 generations away from ever seeing a cat are still averse to cat pheromones

Question 2

What 3 important things happen in the pre-natal environment?

Answer 2

Circulating hormones (from mother and from rat siblings strung up on the same circulatory chain)
Glucocorticoids and other stress hormones. High exposure to these brings, as an adult, smaller brain, lower capacity for learning, more tendency towards anxiety/hypertension/diabetes. Sheesh!
Leads to epigenetic effects of inability to shut down stress response thanks to smaller hippocampus
Maternal and sibling estrogen influences also influence subsequent development (earlier puberty, etc).
Nutrition and metabolic programming
Prime example of epigenetics (non-mendelian inheritance of traits, even multi- generationally, that has nothing to do with genes - are not heritable traits).
We also see pelvic arch size evolutionary battles with Massai malnutrition
Learning mother’s voice

Question 3

Some would say maternal and paternal genetic contributions are equal, and that mom also gives
the prenatal environment.
How would you then explain any differences you saw in behavior as shared more with mom? Due to the influence of the prenatal environment. That’s how we can control for it.
But what complicates that assertion? In what ways is mom more than just 50% genes + prenatal environment?

Answer 3

Paternal uncertainty
􏰀 Mitochondrial DNA
􏰀 Imprinted genes
􏰀 Transcription Factor inequality and Lamarkian inheritance

Question 4

And say we do discover a strong genetic component for something like extroversion. What might the genes actually be influencing? 3 examples:

Answer 4

􏰀 Something indirectly related to extroversion, like attractiveness. These are indirect genetic effects.
􏰀 Another example: high heritability for political affiliation may have to do with the genetics of ambiguity tolerance
􏰀 Aggression in rats also seems highly heritable. Not actually genes for aggression! About pain tolerance
thresholds.

Question 5

How do behavioral geneticists hone in on actual genes?

Answer 5

􏰀 Find genetic differences, then look for differences in behavior.
􏰀 To find genetic differences in order of awesomeness:
o o o o
􏰀 Drawback: it’s about identifying covariants in the genes with the disease, so it’s a statistical relationship and often doesn’t give 100% certainty.
􏰀 Drawback: you do all this work in a family, but then in a different family they’ll have different markers. So multiple genetic routes to a disease.
􏰀 Drawback: even knowing the exact gene, it’s usually not 100% deterministic

Question 6

Or the reverse: find variations in genes and then study “where the light is” to figure out its effects. What three examples do we have?

Answer 6

􏰀 Vasopressin receptor variants. Not just voles, also humans! The “monogamous” promoter version makes for more stable marriages and greater facial expression-reading ability in humans!
􏰀 Variants in BDNF in humans predict risk of anxiety and amygdalar metabolic rate (same with a
neurotransmitter called NPY).
􏰀 Variants in dopamine and serotonin receptors and risk-taking
􏰀 Criticism: Looking where the light is. By looking where there is an expected effect, they’ve eliminated the chance
to find an unexpected effect.
􏰀 Criticism: multiple genes affect the same outcome behaviors sometimes. Therefore one single gene variant
probably has very small effects. You won’t be illuminating complex human behavior.

Question 7

What does heritability tell us?

Answer 7

􏰀 Heritability DOES tell you the degree to which the variance of a trait is influenced by genes.
􏰀 Heritability DOES NOT tell you the degree to which a trait (the average of the trait) is influenced by genes, or how
much a trait “is genetic.”
􏰀 The fact that humans usually have 10 fingers reflects the fact that this trait is inherited. But cases where humans
have fewer than 10 fingers involves 0% heritability.

Question 8

How do we know if something is highly heritable?

Answer 8

􏰀 Look at the variation in a trait and ask yourself did that variation result from differences in genes or differences in the environment? If it’s differences in genes then it’s highly heritable.
􏰀 For traits that are highly heritable, then knowing the gene will give you huge predictive power over the variation displayed in your trait of interest.
􏰀 For traits that are not highly heritable, knowing the environment or some other factor will give you more explanatory power over the variance in your trait of interest.

Question 9

And for one more complication, what role does chance play in the development of an organism?

Answer 9

􏰀 Particularly in the splitting of cells, brownian motion (unpredictable, probabilistic movement of atoms and molecules) will not cause equal 50-50 splits of all the Transcription Factors and hormones and other cytoplasmic things.