Lecture 12 Human-Agricultural Coevolution

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11 Apr 2012
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Lecture 12 BIO 220
Coevolution (Sexual, Human agricultural)
Reciprocal evolutionary responses in:
oA pair of species, caused by selection imposed by each other
Evolution by natural selection is a genetic and ecological process
oEcology produces selection
oGenetics provides the material that is transmitted across generations
For humans, ecology includes culture and the organisms we interact with
Human infants depend on milk
Lactase production normally declines in adulthood
oException: people of north European origin
oDecline in lactase “lactose intolerance”
oWild type: lactose intolerance in adulthood
Lactase Persistence
Lactase production persists through adulthood, allowing digestion of milk
Evolution in European Cattle farming cultures
Observation: changes in lactase gene correlated with ability to digest lactose as
adult.
Hypothesis: substitutions are causal variants, they were formed by natural selection
Predictions
If substitutions in lactase gene cause lactase persistence, other human populations
with lactase persistence would have same substitutions, or changes with similar
consequences
If dairy agriculture evolution on substitutions that cause lactase persistence,
other human populations practicing dairy agriculture should have lactase
persistence phenotype, visible genetic evidence of past selection on lactase gene.
African cultures with dairy agriculture have distinctive forms of lactase gene
oDNA differences correlate with ability to digest lactose
Change vs. Determinism
Single events can be due to change alone or o deterministic processes
Independent lines of evidence can confirm deterministic explanations by rejecting
chance
Convergent evolution
Independent evolution of same trait in different groups
oGroups can be population or species
Allow more confident determination that selection is at work
Appears to use same genes
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