Natural Selection

Charles Darwin—English scientist

(1831—sailed for 5 years on HMS Beagle)

Studied fossils and collected biological specimens

On the Galapagos islands Darwin studied many plants and animals, but specifically a type of bird—finches.

*He discovered the birds had changed due to isolation on each island, and had evolved different traits to meet survival needs of each island (ex: beak size, coloration, wing span, etc.)

*He proposed the idea of Natural Selection

NATURAL SELECTION—a mechanism for change in a population

-Occurs when organisms in a population with favorable variations survive, reproduce and pass their variations to the next generation

*Darwin’s theory proposes adaptations in species develop over many generations

Ex: mole rats live underground and are blind. They once had site, but over time, blindness was naturally selected for since it was a disadvantage

*Most structural adaptations develop over millions of years (this is a SLOW process)

VESTIGIAL STRUCTURES: body structure in a present-day organism that no longer serves its original purpose, but was probably useful to an ancestor ex: (a whale’s pelvic bone, a human’s appendix)

Mechanisms of Evolution:

Evolution: a change in a population over time

(evolution is often a result of natural selection)

GENE POOL: all the alleles of the population’s genes together (due to possibilities of breeding )

*sometimes a gene pool in a population is limited due to a population being separated due to environmental changes (ex: a highway being built through a forest, etc.)

SPECIATION: the evolution of new species when members of a similar population no longer intrebreed to produce fertile offspring with their natural environment

*This is what happened with Darwin’s finches on each separate island, they became so different, they eventually became a new species of finch.

DIVERGENT EVOLUTION: pattern of evolution in which species that once were similar to an ancestral species diverge or become increasingly distinct/when a population changes

CONVERGENT EVOLUTION: occurs when unrelated species occupy similar environments in different parts of the world / a pattern of evolution in which distantly related organisms evolve similar traits