Unit 1 Evolution: Week 2 — Evidence for Evolution (Video Notes)

3 Conditions for Natural Selection

Heritable variation: phenotypic variation among individuals must be genetically transmissible to the next generation.
Differential reproductive success: this variation must lead to differences in lifetime reproductive success (fitness).
Population variation: phenotypic variation must exist in the population.

Beak depth/shape variation relates to foraging; drought favors deeper, stronger beaks (large seeds).
After droughts, deeper beaks have higher survival; after normal rains, average beak depth decreases again.
Grants observed year-to-year shifts in average beak depth, consistent with evolutionary change via natural selection.

Color controlled by a single gene; dark allele is dominant.
Frequency of melanic moths rose near industrial centers as pollution darkened trees.
Pollution controls later lightened tree bark; lighter moths became dominant again.

Change initiated by humans; selects for traits that improve reproduction and gene transmission.
Directional selection leading to evolutionary change (example: Drosophila bristle number).
Agricultural selection: breeding for traits like higher milk production or larger corn ears.

Human-imposed selection yields a variety of breeds (cats, dogs, pigeons, etc.).
Some breed differences exceed differences between Canid species.
Domestication can drive unintended selection for other traits (pleiotropy/linkage).

Chosen for docility; after ~40 years, docility increased, but many dog-like physical traits appeared.
Traits for behavior may be linked to other traits via pleiotropy or genetic linkage.

Fossilization is rare; process involves burial, mineralization, and rock formation; fossils are preserved remains of once-living organisms.
Absolute dating:
- t_{1/2} = 1.25 imes 10^{9} ext{ years} ext{ for } ^{40} ext{K}
- t_{1/2} = 5700 ext{ years} ext{ for } ^{14} ext{C}
Fossils inform about rates and patterns of evolution; e.g., modern horse diversity and molar size changes over time.

Homologous structures: different forms/functions, same common ancestor (e.g., forelimbs of mammals share a common bone structure).
Early embryonic development: vertebrate embryos often similar early on; pharyngeal pouches develop into different structures (humans: glands/ducts; fish: gill slits).
Comparative embryology highlights conserved developmental pathways.
Vestigial structures: reduced/unused traits that resemble ancestral features (e.g., human ear muscles; hip bones in boas; digits in flippers of manatees).
Pseudogenes: nonfunctional remnants of once-functional genes (e.g., icefish have nonfunctional hemoglobin gene).

Biogeography studies geographic distribution of species; similar environments yield similar appearances in distantly related groups.
Convergent evolution: similar forms evolve in separate lineages due to similar selective pressures, not shared ancestry.
Examples: Australian marsupials vs placental mammals; convergent forms in fast-moving marine predators (sharks, tuna, ichthyosaurs, dolphins).
Convergent evolution can fill similar ecological roles across regions.

Humans and birds share features like a 4-chamber heart and endothermy; these are examples of convergent evolution rather than homologous traits.
How to tell: look for shared ancestry vs independent development under similar pressures.

Explain why beak depth changes yearly for Daphne Major finches and why pepper moth survival depends on environment.
Define Adaptation, Natural Selection, Variations (in an evolutionary sense), and Artificial Selection; provide brief examples.
What is an intermediate fossil form?
Explain convergent evolution with an example.
Define biogeography, homology, and population.
What is a vestigial structure? Provide at least two examples for humans and other wildlife.