Gene-Culture Co-Evolution Kevin N. Laland

1. Gene-Culture Co-Evolution Kevin N. Laland Centre for Social Learning and Cognitive Evolution School of Biology University of St. Andrews www.st-andrews.ac.uk/~seal

2. Hominin stone tools (Figure fromFoley, 1995)

3. Animal Traditions

4. Development Development Gene pool Culture t Modified selection Modified selection Cultural inheritance Genetic inheritance Time Gene pool Culture t+1

5. Recent positive selection in the human genome • In the last 100,000 years humans have • spread from East Africa around the globe, • experienced an ice-age, • undergone a transition from hunter-gatherer to agricultural societies, • witnessed rapid increases in densities, • new proximity of farmers to animal pathogens.

6. Recent positive selection in the human genome • In the last 100,000 years humans have • spread from East Africa around the globe, • experienced an ice-age, • undergone a transition from hunter-gatherer to agricultural societies, • witnessed rapid increases in densities, • new proximity of farmers to animal pathogens. • Recent statistical analyses of genetic data reveal hundreds of human genes that show signals of very strong and recent selection (e.g. in response to malaria, dairy farming etc). • (Wang et al., 2006; Voight et al., 2006).

7. Recent positive selection in the human genome “Homo sapiens have undoubtedly undergone strong recent selection for many different phenotypes…. Given that most of these selective events likely occurred in the last 10,000-40,000 years…it is tempting to speculate that gene-culture interactions directly or indirectly shaped our genomic architecture.” (Wang et al., 2006, PNAS p140).

8. Pioneers of gene-culture co-evolution Edward O. Wilson Cavalli-Sforza & Feldman Boyd & Richerson

9. Gene Unit of cultural information Gene pool Culture pool Genetic inheritance Cultural transmission Natural selection Cultural selection Mutation Innovation Random genetic drift Random cultural drift Parallels between genetic and cultural processes

10. Natural and cultural selection Some cultural traits have a direct effect on survival and natural selection may change their frequency (e.g. smoking). Other traits spread due to cultural selection (e.g. blue jeans, frisbee).

12. Vertical Parents

13. Vertical Oblique Parents Teacher, Leader, Elder

14. Vertical Oblique Parents Horizontal Friend

15. Transmission biases There may be biases in cultural transmission. i) Direct bias – given a choice between two or more alternatives, genetic predisposition or prior knowledge may favour certain types of information being adopted. ii) Frequency-dependent bias - the frequency of a trait affects the probability of information transmission, e.g. conformity.

16. Dairy farming and lactose absorption Human adults require the enzyme lactase to break down the protein lactose that is present in cows’ milk. Whether or not an adult can digest lactose is largely down to whether he/she possesses the appropriate copy of specific genes.

17. Researchers have found that there is a strong correlation between the incidence of the gene for lactose absorption and a cultural history of dairy farming. Milk products have been a part of some human diets for 6000 years Ulijaszek & Strickland (1993)

18. Feldman and Cavalli-Sforza (1989) modelled the relationship between the spread of the gene for lactose absorption and the spread of the cultural trait. Their analysis supported the hypothesis that the cultural practise of dairy farming created the selection pressure favouring this gene.

19. A phylogenetic analysis of human societies by Holden & Mace (1997) supported the dairy farming hypothesis and revealed that dairy farming evolved prior to the spread of genes for lactose absorption.

20. Applications of gene-culture models 1. Inheritance of behavioural and personality traits (Cavalli-Sforza and Feldman, 1973; Otto et al., 1995). 2. Adaptive advantages of learning and culture (Rogers, 1988; Boyd and Richerson, 1985; Feldman et al., 1996). - cultural group selection (Boyd & Richerson, 1985) 3. Application to specific cases: - evolution of language (Aoki & Feldman, 1987, 1989) - excess female mortality and sex-ratio evolution (Kumm et al., 1994) - sexual selection (Laland, 1994) - evolution of handedness (Laland et al., 1995) - the emergence of incest taboos (Aoki & Feldman, 1997) - cultural niche construction (Laland et al., 2001) - evolution of prestige (Henrich & Gil-White, 2001)

22. Human Sociobiology Evolutionary Psychology Evolutionary approaches to the study of human behaviour Historical approach Contemporary approaches: Human Behavioural Ecology Gene-Culture Co-evolution Cultural evolution

23. Fisherian Runaway Sexual Selection 1 Trait (T2) 0 0 1 Preference (P2) Kirkpatrick (1982)

24. Unbiased Vertical Cultural Transmission 1 Genetic Trait (T2) 0 Cultural 0 1 Preference (P2) Laland(1994)

25. Biased Transmission favouring P2 + 1 Trait (T2) + + 0 Cultural 0 1 Preference (P2)

26. Predictions and applications There should be society-wide correlations between culturally transmitted preferences and gene-based traits (in both sexes) The hypothesis could apply to many traits: e.g. skin colour, facial features, facial and body hair, body shape, height, degree of character symmetry, degree of neoteny, level of aggressiveness, emotionality