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Transcript
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
Hominin stone tools
(Figure fromFoley, 1995)
Animal Traditions
t+1
Development
Gene
pool
Culture
Cultural
inheritance
Modified
selection
Genetic
inheritance
Time
t
Gene
pool
Development
Modified
selection
Culture
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).
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).
Pioneers of gene-culture co-evolution
Edward O. Wilson
Cavalli-Sforza & Feldman
Boyd & Richerson
Parallels between genetic and cultural processes
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
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).
Vertical
Parents
Vertical
Oblique
Parents
Teacher, Leader, Elder
Vertical
Oblique
Parents
Horizontal
Friend
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.
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.
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.
Ulijaszek & Strickland (1993)
Milk products have been a part of some human diets for 6000 years
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.
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.
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)
Evolutionary approaches to the study of human behaviour
Historical approach
Human Sociobiology
Contemporary
approaches:
Human
Behavioural
Ecology
Evolutionary
Psychology
Cultural
evolution
Gene-Culture
Co-evolution
Fisherian Runaway Sexual Selection
1
Trait (T2)
0
0
Preference (P2)
1
Kirkpatrick (1982)
Unbiased Vertical Cultural Transmission
1
Genetic
Trait (T2)
0
0
Cultural
Preference (P2)
1
Laland(1994)
Biased Transmission favouring P2
1+
Trait (T2)
0+
0
Cultural
Preference (P2)
+
1
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