Evolutionary Biology: Darwin's Evidence

Flashcards covering Darwin's hypothesis of natural selection, evidence from his time, modern supporting evidence, and the implications of his theory, drawing from the provided lecture notes.

Natural Selection

The process by which individuals that vary slightly in profitable ways under varying life conditions have a better chance of surviving and thus are naturally selected, propagating their new and modified form.

Darwin's Hypothesis (Three parts)

1. There must be variation in the population. 2. Variation must lead to differences among individuals in lifetime reproductive success. 3. Variation must be transmitted to the next generation.

Darwin's Hypothesis (Five parts)

1. Individuals vary. 2. Populations tend to overbreed relative to available resources, leading to a struggle for survival. 3. Better variations have better survival (survival of the fittest). 4. Survivors will reproduce and non-survivors won’t. 5. Traits leading to better survival and reproduction must be heritable.

Individual Variation

The observation that individual differences exist within natural populations, as exemplified by Powelliphanta land snails or Dog strangling vine.

Overbreeding and Struggle for Survival

The tendency of populations to produce more offspring than can survive, given available resources, resulting in a competition for existence (e.g., thousands of oak acorns yielding only 1-10 mature trees).

Rosemary Grant and Peter Grant

Renowned researchers who conducted long-term studies on natural selection in the medium ground finch on Daphne Major in the Galápagos Islands.

Daphne Major

A small island in the Galápagos archipelago that served as the primary field site for the Grants' research on finch evolution.

Medium Ground Finch (Geospiza fortis)

The species of finch studied by the Grants, known for exhibiting variation in beak size that is subject to natural selection based on environmental conditions.

1977 La Niña (Daphne Major)

A severe drought event that led to withered vegetation and the scarcity of small, soft seeds, favoring the survival and reproduction of medium ground finches with larger, harder beaks.

1984/1985 El Niño (Daphne Major)

An unusually wet period that resulted in abundant vegetation and a high concentration of small, soft seeds, which would likely favor finches with smaller beaks.

Heritability

The principle that traits leading to better survival and reproduction can be passed down from parents to offspring, a crucial component of natural selection.

Age of the Earth (Darwin's Implication)

One implication of Darwin's hypothesis requiring the Earth to be old enough for gradual evolutionary changes to have occurred, supported by the geological work of Hutton and Lyell.

Fossils and Species Mutability

Fossil evidence from Darwin's time and early modern geology demonstrated that species change over time (are mutable), supported by Cuvier's findings on extinction and Darwin's own fossil discoveries.

Cuvier

A scientist who, prior to Darwin, showed that extinction occurred and that certain past species were no longer in existence.

Archaeopteryx

A famous fossil, found in London (1861) and Berlin (1876/77), considered a transitional form between birds and reptiles due to its mix of features like wings and feathers (bird) and bony tail and teeth (reptile).

Whale Transitional Forms

Fossil evidence, including Pakicetus attocki, Ambulocetus natans, and Rodhocetus kasrani, that illustrates the evolutionary pathway from land-dwelling ancestors to modern aquatic whales.

Tiktaalik

A transitional fossil form found to bridge the gap between fish and amphibians, showing adaptations for both aquatic and terrestrial environments.

Equidae (Horse Lineages)

A classic example in the fossil record demonstrating evolution over millions of years, showing gradual transitions in features such as size, foot structure, teeth, and habitat/feeding behavior.

Hyracotherium

Considered to be the likely first 'horse,' characterized by its small size, short legs, broad feet with multiple toes, small and simple teeth, and a forest browsing diet.

Missing Links (Problem)

The conceptual issue that finding one transitional fossil (a 'missing link') often creates two new 'missing links' in the evolutionary chain, as it clarifies relationships while highlighting new gaps.