Chapter 5 Notes - EVOLUTION

Darwin’s Voyage

Darwin thought that species gradually changed over many generations as they became better adapted to new conditions. This process is called evolution.

Darwin’s observations led him to propose that evolution occurs through natural selection. Natural selection occurs due to overproduction, competition, and variation.

As scientists after Darwin learned, only traits that are inherited, or controlled by genes, can change over time as a result of natural selection.

If a group of individuals remains separated from the rest of its species long enough to evolve different traits, a new species can form.

species – a group of similar organisms that can mate with each other and produce fertile offspring

adaptation – a characteristic that helps an organism survive in its environment and reproduce

evolution – the gradual change of a species over time

scientific theory – a well-tested concept that explains a wide range of observations

natural selection – the process by which individuals that are better adapted to their environment are more likely to survive and reproduce than other members of the same species

variation - any difference between individuals of the same species

The Fossil Record

Most fossils form when organisms die and sediments bury them. The sediments harden, preserving parts of the organism.

Most of what scientists know about extinct species is based on the fossil record. The fossil recode provides clues about how and when new groups of organisms evolved.

How fast does evolution occur?

Gradualism – tiny changes add up to major changes over very long periods

Punctuated Equilibria – evolution occurs during short period of rapid change separated by long periods of little change

fossil – the preserved remains or traces of an organism that lived in the past

fossil record – the millions of fossils that scientists have collected

extinct – a species that does not have any living members

gradualism – the theory that evolution occurs slowly but steady

punctuated equilibria – the theory that species evolve during short periods of rapid change

Other Evidence for Evolution

By comparing modern-day organisms, scientists can infer how closely related they are in an evolutionary sense.

To determine the evolutional relationship between organisms scientists:

- Compare Body Structures

- Similarities in Early Development

- Similarities in DNA

homologous structures – body parts that are structurally similar in related species; provide evidence that the structures were inherited from a common ancestor

branching tree – a diagram that shows how scientists think different groups of organisms are related