BSCI Topic 2: Charles Darwin and Natural Selection Exam Prep

Prepare

Charles Darwin (1809 – 1882)

a. Privileged background, trained in medicine/religion but interested in natural history, field biology/geology

b. When he was only 22, opportunity to go on a round-the-world exploratory expedition – Voyage of the Beagle

i) Know when – 27 December 1831 to 2 October 1836

ii) Know general path – field observations in the Galapagos particularly important, also South Pacific (coral reefs)

iii) Developed the idea of natural selection on this trip, spent the rest of his life developing the idea, testing it, amassing huge amounts of data

Voyage of the Beagle (1831–1836)

Darwin observed species and fossils worldwide; key insights from Galápagos finches and tortoises.

Darwin’s major works

1. Voyage of the Beagle (1839)

2. Coral Reefs (1842)

3. On the Origin of Species (1859)

4. Descent of Man (1871)

Alfred Russel Wallace

Co-discoverer of natural selection; worked in the Malay Archipelago.

Darwin’s 5 Premises of Natural Selection:

1. Variation exists among individuals.

2. Variation is heritable.

3. More offspring are produced than can survive.

4. Individuals with favorable traits reproduce more.

5. Populations change over generations.

Darwin’s problem

Believed in blending inheritance, which erased variation; later resolved by Mendel’s particulate inheritance.

Evidence for Evolution: Groups within groups

Hierarchical classification reflects shared ancestry.

Evidence for Evolution: Homology

Similar structures from a common ancestor (e.g., vertebrate forelimbs).

Evidence for Evolution: Vestigial structures

Reduced or unused features inherited from ancestors (e.g., whale pelvis, human appendix).

Evidence for Evolution: Fossil record

Shows transitional forms and gradual change over time.

Evidence for Evolution: Biogeography

Geographic distribution of species reflects evolutionary history (e.g., island endemics).

Evidence for Evolution: Geology and plate tectonics

Explain fossil distribution and species divergence.

Evidence for Evolution: Direct observation

Evolution observed in real time (e.g., antibiotic resistance).

Types of Natural Selection: Directional selection

One extreme favored (e.g., antibiotic resistance).

Types of Natural Selection: Stabilizing selection

Intermediate traits favored (e.g., human birth weight).

Types of Natural Selection: Disruptive selection

Both extremes favored (e.g., seedcracker finches).

Types of Natural Selection: Balancing selection

Maintains genetic diversity in population.

Types of Natural Selection: Frequency-dependent selection

Fitness depends on allele frequency (e.g., cichlid mouth direction).

Types of Natural Selection: Heterozygote advantage

Heterozygotes have higher fitness (e.g., sickle-cell trait).

Types of Natural Selection: Sexual selection

Traits evolve for mating success, not survival (e.g., peacock tail).

Types of Natural Selection: Clines

Gradual change in traits across geography (e.g., body size vs. latitude).