Evolution and Natural Selection Study Guide

Comprehensive practice flashcards covering natural selection, population genetics, evidence of evolution, phylogenetics, speciation, and early Earth history.

How is natural selection defined?

The mechanism of evolutionary adaptation where organisms better suited to their environment are more likely to survive and reproduce.

What are the 5 key points of Darwin's mechanism of natural selection?

Overpopulation, Variation, Competition, Fitness, and Reproduction.

How is evolutionary fitness measured?

By reproductive success (how many surviving offspring an organism produces), not just lifespan.

What are the three types of selection and how do they alter population curves?

Directional Selection shifts the curve toward one extreme phenotype; Stabilizing Selection favors the average/intermediate phenotype and narrows the curve; Disruptive Selection favors both extremes, selects against the average, and creates a bimodal curve.

What is artificial selection, and what examples are provided in the notes?

Human-driven evolutionary pressure where humans select desired traits to breed; examples include wild mustard bred into kale, broccoli, and cabbage, as well as wolf ancestors bred into diverse dog breeds.

What are three crucial misconceptions to avoid regarding evolution and natural selection?

1. Teleology (evolution is goal-oriented): Evolution has no final goal or ultimate purpose.
2. Natural selection is a random process: It is non-random because survival is determined by environmental pressures.
3. Individuals evolve: Populations evolve, not single individuals.

What is the sequence of the Central Dogma of Molecular Biology?

$$\text{DNA} \rightarrow \text{RNA} \rightarrow \text{Protein} \rightarrow \text{Trait(Phenotype)}$$

What is the biological definition of evolution in population genetics?

The change in allele frequencies in a population over time.

What are the two forms of genetic drift described in the notes?

The Bottleneck Effect (population size is drastically reduced by a random disaster/event like a forest fire or hunting) and the Founder Effect (a small group splits off to colonize a new area, altering allele frequencies).

What is the ultimate raw source of all new genetic variation?

Mutations (changes to DNA sequences).

What is biogeography and what observation does it explain?

The study of species distribution. It observes that organisms living closer geographically tend to be more closely related (such as in Wallace's study of marsupials vs. placental mammals).

How do homologous, analogous, and vestigial structures differ?

Homologous structures share physical features from a common ancestor via divergent evolution (e.g., mammalian forelimbs). Analogous structures have similar functions evolved independently through convergent evolution (e.g., bird and insect wings). Vestigial structures are homologous features that no longer serve a major purpose (e.g., human tailbone, snake hind leg bones).

What biochemical evidence points strongly to a single common ancestor for all life?

All life shares the same universal genetic code (DNA/RNA) and fundamental metabolic pathways (such as glycolysis).

How does radiometric dating determine the absolute age of fossils and rocks?

It measures the radioactive decay of isotopes (like Carbon-14) using half-lives.

What are the key components of a phylogenetic tree?

The Root (ancestral lineage/common ancestor of all groups), Nodes (branch points representing divergence events), and the Outgroup (the lineage least closely related to the rest of the organisms on the tree).

What is the primary difference between a cladogram and a phylogenetic tree?

A cladogram has branch lengths that are usually equal and shows hypothetical relationships without tracking exact time or distance; a phylogenetic tree has branch lengths proportional to evolutionary time or genetic distance.

What is maximum parsimony?

The scientific assumption that the simplest explanation with the fewest evolutionary steps or mutations is most likely correct.

What is the Biological Species Concept?

A definition stating that a species is a group of populations whose members can interbreed in nature and produce viable, fertile offspring.

What distinguishes allopatric speciation from sympatric speciation?

Allopatric speciation is driven by a geographic barrier (e.g., the Isthmus of Panama separating porkfish), whereas sympatric speciation occurs without a geographic barrier (driven by polyploidy, habitat differentiation, or sexual selection).

What are the four prezygotic barriers listed in the notes?

Habitat/temporal isolation, behavioral isolation, mechanical isolation (e.g., structural incompatibilities in bushbaby genitalia), and gametic isolation (e.g., gametes cannot fuse in sea urchins).

What are the three postzygotic barriers listed in the notes?

Hybrid inviability, hybrid infertility (e.g., a sterile mule produced by a horse and donkey), and F2 breakdown.

How do gradualism and punctuated equilibrium differ as models for rates of evolution?

Gradualism consists of slow, steady, continuous changes over long periods, while punctuated equilibrium consists of long periods of stasis interrupted by brief, rapid bursts of significant change.

What happens during divergent evolution and adaptive radiation?

One species splits into multiple diverse species from a common ancestor; in adaptive radiation, species rapidly fill open ecological niches (e.g., Darwin's finches).

Why is genetic variation crucial for population survival, and what example of low variation is provided?

High genetic diversity gives resilience against environmental pressures; low variation makes populations extremely vulnerable to being wiped out by disease (e.g., agricultural monocultures or cloned crops like the Gros Michel banana).

What are the key events and dates in Earth's history highlighted in the notes?

$\sim 4\text{ billion}$ years ago: Hot young Earth, heavy volcanic activity, no oxygen. $\sim 3.5\text{ billion}$ years ago: First life (prokaryotes) and first photosynthetic organisms. $\sim 2.4\text{ billion}$ years ago: Great Oxygenation Event / Banded Iron formations. $\sim 2\text{ billion}$ years ago: Development of Eukaryotes via Endosymbiosis.

What does the Endosymbiotic Theory propose, and what evidence supports it?

An anaerobic prokaryote engulfed an aerobic bacterium (becoming mitochondria) and/or photosynthetic cyanobacteria (becoming chloroplasts). Supporting evidence includes mitochondria and chloroplasts having their own circular DNA, double membranes, and reproducing independently via binary fission-like division.

What is the RNA World Hypothesis?

The hypothesis proposing that RNA was the first genetic material because it can store genetic data, self-replicate, and act as an enzyme (catalytic activity).