1. Gene-Culture Interactions in Humans Lalande, KN (2008) Phil Trans Roy Soc B 363:3577—3559.

2. Human Genetic Evolution 25,000 genes: Few hundred to few thousand show molecular signature of recent, strong selection Selected alleles: 15% influence neuronal function Some known (some unknown) brain functions Human brain remodeled recently (10 5 yrs?) (vs evolutionary psychology)

3. Human Genetic Evolution Last 10 5 years: Ice age (environmental) Dispersed over 5 continents Population densities grown Developed agriculture Proximity to animals – new diseases Last 4: human activity (cultural niche construction) may have modified selection pressures on human genes

4. Niche construction: basis for gene-culture coevolution Dairy farming favored lactose-adsorption allele Kwa-speaking yam cultivators (West Africa) Cut clearings in forest to grow crop Clearings: pools of standing water Water: habitats for larval mosquitos Malaria prevalence increased strongly

5. Niche construction: basis for gene-culture coevolution Kwa-speaking yam cultivators (West Africa) Malaria prevalent Natural selection favored sickle-cell S allele Heterozygote protected against malaria and avoided costs of anemia (heterosis)

6. Niche construction: basis for gene-culture coevolution Kwa-speaking yam cultivators (West Africa) Other Kwa groups, different agriculture No increase in S allele Implication: Cultural practice led to natural selection acting on members of culture

7. Genes and Culture Genetic propensities Expressed through development Influence what is learned Socially and individually Learning can (often) coincide with genetic influence on behavior Learning can counter selectively favored behavior

8. Evolution of handedness Why isn’t everyone right-handed?

9. Handedness  90% humans right-handed worldwide Chimpanzees show lesser degree (?) Genetic propensity for right/h among humans Pr[right/h] = ½ + genetic effect + …

10. Handedness Among Cultures Handedness frequency varies across cultures; None with left-handed majority Some cultures view left-handedness as “wrong” Identical twins no more alike than fraternal twins Taiwan: 0.7% write left/h Taiwanese in US: 6.5% write left/h Pr[right/h] = ½ + genetic effect + cultural effect

11. Handedness: Current Model Handedness develops by 2 – 3 years of age Birth: Pr[right/h] = p = ½ + genetic effects p=0.78  Genetic bias for right/h = 0.28 Independently of parents’ handedness, genetic propensity toward right/h

12. Handedness: Current Model At Birth: Pr[right/h] = p = ½ + genetic effects p=0.78 Cultural effects Vertical: Mimicry, instruction Apparently cancel when 1 parent right/h; other parent left/h

13. Handedness: Current Model Pr[right/h] = p = 0.78 + cultural effects Two parents right/h p = 0.78 + 0.14 = 0.92 Two parents left/h p = 0.78 – 0.14 = 0.64 Genetic propensity twice cultural effect BUT left-handedness persists