Unit 6: Genetics, Evolution, and Behavior
How twin studies estimate the genetic share of a trait, and how natural selection explains behavior without explaining it away.
4 topics · 12 questions
Each topic is a path, not a menu: work down it in order and every question builds on the one above. Click any of them to watch the answer draw itself.
Twin and Adoption Studies
- How it worksHow does comparing identical twins to fraternal twins let researchers estimate how heritable a trait is?
- Worked exampleFind the rough heritability of a trait where identical twins correlate at 0.80 and fraternal twins correlate at 0.40.
- Common mistakeWhy doesn't a heritability of 50 percent mean half of any one person's trait came from their genes?
Your turn1 of 2
Find the rough heritability of a trait where identical twins correlate at 0.774 and fraternal twins correlate at 0.38.Genes Set a Range, Not a Fate
- How it worksHow does a gene's reaction range let environment push a trait up or down within limits the genes set?
- Common mistakeWhy isn't finding a gene for a behavior the same as that gene guaranteeing the behavior?
- Going furtherWhat happens to a trait's expressed range when every person in a population grows up in an identical environment?
Your turn1 of 2
Two people with identical genes for height can end up quite different heights if one grew up with poor childhood nutrition and the other with excellent nutrition. A student assumes this must mean genes have very little real influence on height at all, since environment alone seems to be deciding the outcome. What does a gene's reaction range actually explain here?Natural Selection and Behavior
- How it worksHow does natural selection build a behavior into a species the same slow way it builds a wing or an eye?
- Going furtherWhat happens to an evolved fear response, like fear of spiders, when it is deliberately unlearned through exposure?
- Common mistakeWhy doesn't an evolved preference mean that preference is impossible for culture to override?
Your turn1 of 2
Human babies come into the world already able to recognize and prefer looking at a face, without ever having been taught to do so. A student assumes such a specific behavioral tendency could only ever come from learning after birth, the same way a person learns to read. How does natural selection build a behavior into a species the same slow way it builds a physical structure like a wing or an eye?The Environment of Evolutionary Adaptedness
- How it worksHow does a mismatch between the ancestral environment and the modern one turn a once-useful instinct into a liability?
- Going furtherWhat happens to a craving for salt, once life-saving on the savanna, in a world where salt is in every processed food?
- Ties togetherHow does the idea of an evolutionary mismatch connect to why junk food is so hard to resist?
Your turn1 of 2
Craving sugar and fat made excellent sense for ancestors living where calories were scarce and unpredictable, but that same craving now sits someone in front of a vending machine stocked with cheap, calorie-dense snacks at every turn. A student assumes an instinct that made sense once should still make just as much sense now, in any environment. How does a mismatch between the ancestral and modern environment turn a once-useful instinct into a liability?