Gene-Culture Co-Evolution

Kevin N. Laland

Centre for Social Learning and Cognitive EvolutionSchool of Biology

University of St. Andrewswww.st-andrews.ac.uk/~seal

Hominin stone tools

(Figure fromFoley, 1995)

Animal Traditions

Tim

et

t+1

Genepool

Genepool

Gen

etic

inhe

rita

nce

Culture

Culture

Cul

tura

lin

heri

tanc

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Development

Modifiedselection

Development

Modifiedselection

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 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).

“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).

Recent positive selection in the human genome

Edward O. Wilson

Cavalli-Sforza & Feldman Boyd & Richerson

Pioneers of gene-culture co-evolution

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

Natural and cultural selection

Other traits spread due to cultural selection (e.g. blue jeans, frisbee).

Some cultural traits have a direct effect on survival and natural selection may change their frequency (e.g. smoking).

Vertical

Parents

Vertical

Oblique

Parents Teacher, Leader, Elder

Horizontal

Vertical

Oblique

Parents

Friend

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.

Transmission biases

Human adults require the enzyme lactase to break down theprotein lactose that is present in cows’ milk.

Whether or not an adult can digest lactose is largely down towhether he/she possesses the appropriate copy of specific genes.

Dairy farming and lactose absorption

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)

Feldman and Cavalli-Sforza (1989) modelled the relationship between the spread of the gene for lactose absorption and thespread of the cultural trait.

Their analysis supported the hypothesis that the cultural practise of dairy farming created the selection pressure favouring this gene.

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.

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)

Applications of gene-culture models

Culturalevolution

HumanBehavioural Ecology

Contemporaryapproaches:

EvolutionaryPsychology

Gene-CultureCo-evolution

Historical approach

Human Sociobiology

Evolutionary approaches to the study of human behaviour

0 10

1

Preference (P2)

Trait (T2)

Fisherian Runaway Sexual Selection

Kirkpatrick (1982)

0 10

1

Preference (P2)

Trait (T2)

Unbiased Vertical Cultural Transmission

Cultural

Genetic

Laland(1994)

0 10

1

Preference (P2)

Trait (T2)

Cultural++

+Biased Transmission favouring P2

The hypothesis could apply to many traits:

e.g. skin colour, facial features, facial and body hair, body shape, height, degree ofcharacter symmetry, degree of neoteny, level of aggressiveness, emotionality

Predictions and applications

There should be society-wide correlations between culturally transmitted preferences and gene-based traits (in both sexes)