Evolution by Natural Selection
Key mechanisms, formalisms, and lines of evidence behind evolution by natural selection.
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Questions Covered in This Set
11 cards to master
What are Darwin's three ingredients for natural selection?
Variation among individuals, heritability of that variation, and differential reproductive success (more offspring produced than can survive).
Define evolution in the population-genetic sense.
Change in allele frequencies in a population over time.
Is natural selection the source of new variation?
No. Mutation and recombination generate variation blindly; selection only filters which heritable variants spread.
What is genetic drift?
Random sampling error in allele transmission, strongest in small populations; it can fix variants that confer no advantage, making much molecular evolution effectively neutral.
Write the one-generation allele frequency equation.
p' = p·w_A / (p·w_A + (1−p)·w_a), where w_A and w_a are relative fitnesses and p is the starting frequency of A.
How powerful is a 1% fitness advantage?
An allele with w_A = 1.01 goes from ~0.01% to near-fixation in roughly 2,000 generations — about a month for bacteria dividing every 20 minutes.
Why is Tiktaalik a famous prediction-confirming fossil?
Shubin's team searched 375-million-year-old rock *because* theory predicted that age, and found a fish with a neck, wrist bones, and a flat crocodilian head.
What does the broken GULO gene show?
Humans and other primates share the same broken vitamin-C synthesis gene broken at the same nucleotides — a shared error indicating shared ancestry (dogs still make vitamin C).
Why are endogenous retroviruses strong evidence for common descent?
Thousands sit at identical genomic positions in humans and chimpanzees; identical insertion sites are shared errors, like matching mistakes in plagiarism cases.
Name the whale transitional series.
Pakicetus → Ambulocetus → Basilosaurus, showing progressively shrinking hind limbs.
What does Dobzhansky's famous line mean?
"Nothing in biology makes sense except in the light of evolution" — common descent with modification explains universal patterns like the shared genetic code and ATP currency.
