Chapter 11 Flashcards
(46 cards)
What are the two main lines of evidence for the current natural selection going on?
- Evidence from the genome
- evidence based on measuring reproductive success at the phenotypic level
What is purifying selection and how does it affect human genetics?
Purifying selection removes harmful mutations from the gene pool. It is evidenced by high rates of spontaneous abortion due to genetic abnormalities and the existence of Mendelian diseases that impair survival or reproduction.
What is directional selection, and how is it evident in the human genome?
Directional selection favors beneficial alleles that are increasing in frequency. Around 7% of human genes show signs of ongoing positive selection, suggesting adaptive mutations are spreading through populations.
How do scientists detect alleles under positive selection?
By identifying alleles that increase in frequency faster than recombination can shuffle them, creating a pattern of linkage disequilibrium between the allele and nearby genetic sequences.
Why has the rate of human evolution increased in the last 40,000 years? (Hawks et al)
Due to larger population sizes (more variation) and the colonization of new environments (e.g. out of the tropics, agricultural life), which introduced new selection pressures.
How has the shift to agriculture and animal domestication influenced human evolution?
It introduced new selection pressures, especially for immunity, as dense living and contact with animals led to new infectious diseases.
What is stabilizing selection at the phenotypic level? Provide an example.
Stabilizing selection favors average traits. Example: Babies with average birthweights have fewer health problems than those who are very small or large.
What is the evidence for directional selection at the phenotypic level in humans?
Nettle & Pollet (2008) found that male wealth is positively associated with reproductive success across diverse societies.
In Africa: Wealthy men have more wives and children. In industrial societies: Wealthy men are less likely to remain childless, even if total family sizes are similar across classes.
What is the DRD4 gene, and why is it significant in studies of ongoing selection?
DRD4 encodes a dopamine receptor linked to reward-seeking behaviors. It is highly polymorphic and has been studied in relation to genotype and behavioral phenotype.
What are the two main DRD4 genotypes described in the Ariaal study?
7R+ genotype (at least one copy of the 7-repeat allele) and 7R− genotype (no 7-repeat alleles). These variants may influence behaviour and adaptability in different environments.
What is the Ariaal of Kenya study on 7R genotypes and body weight ?
An ethnic group that traditionally practiced nomadic livestock herding.
Part of group settled for 35 years - those with 7R+ genotype more underweight.
What does the Ariaal study suggest about natural selection and human genetics?
That genetic traits like 7R+ can be selected for or against depending on environmental and lifestyle conditions, supporting ongoing human evolution.
What is meant by ‘evolution leaves a legacy’?
Even when selective pressures change, behaviors shaped by past evolution may persist due to their adaptation to ancestral environments.
Give an example of a ‘legacy’ behavior in zoo animals.
Nocturnal animals remain active at night, large carnivores still pace despite no need to hunt, and herbivores remain vigilant despite no predators.
What is New at al.’s study?
Modern humans attend more to animals than to automobiles, despite cars being a greater modern danger—reflecting ancestral survival priorities. Example of the mismatch hypothesis
What is the mismatch hypothesis ?
We are adapted to past environments but not current ones
Contemporary behaviour can’t be understood without some appreciation of evolutionary history
Why do mismatch arguments require caution?
Because they may seem plausible but are hard to verify empirically and may oversimplify complex behaviors.
What is Tinbergen’s framework for explaining behavior?
A four-question model:
1. proximate causation
2. ultimate function
3. ontogeny (development)
4. phylogeny (evolutionary history).
Each is valid and important with its own answer which can be worked on independently
What is the proximate cause of infant crying?
Physical separation from caregiver, cold, hunger; internally, limbic system activation and lack of endogenous opioids.
What is the ultimate function of infant crying?
To elicit care and protection from caregivers, enhancing infant survival and reproductive fitness.
How does infant crying change ontogenetically?
Peaks at 6 weeks, declines after 4 months; after 12 months, becomes more strategic to gain attention rather than from separation.
What is the phylogenetic origin of crying?
Shared across primates, especially species where infants are carried, suggesting a deep evolutionary origin tied to maternal proximity.
What does the crying example illustrate about Tinbergen’s framework?
That understanding behavior requires addressing all four levels: mechanism, function, development, and evolution.
How do evolutionary explanations relate to other human sciences?
They complement rather than oppose sociological, psychological, or anthropological explanations by offering functional and historical context.
