Evolution Evidence and Ideas

Evolution = Change in populations over time

Fossil Evidence remains or traces of past life forms most form from burial of plants & animals in sediment soft parts are often consumed or decomposed but may leave imprints if buried rapidly

How do we know how old it is? Relative dating is done by rock layers (top layers of rock are the youngest) Absolute dating uses radioactive isotopes (using half-lives and isotope amounts)

Extinction death of all members of a species Mass extinction = extinctions of many species in short time. *There have been five mass extinctions so far and many agree we are in the middle of one NOW

Mass Extinctions Following extinctions, remaining groups expand to fill habitats vacated by extinct species. Marine animal fossil record indicates mass extinctions occur every 26 million years--which corresponds to movement of our solar system within Milky Way galaxy.

Biogeographical Evidence Biogeography is the study of the distribution of plants and animals throughout the world Current organism distribution reflects evolutionary history organisms evolve in one location and spread out into other regions no rabbits are found in South America— they originated elsewhere and did not reach South America

Biogeographical Evidence Physical factors limit population range (including location of continents) Continental drift = continents have slowly moved over time distribution of early reptiles across many continents from time when land was attached divided distribution of mammals that evolved after continents parted

Anatomical Evidence Organisms have homologous structures: vertebrate forelimbs contain same sets of bones for different functions

Anatomical Evidence Simplest explanation is a common ancestor whose basic forelimb plan was modified in succeeding groups as each continued along its own evolutionary pathway

Anatomical Evidence Homologous structures are similar structures derived through descent from a common ancestor but may have different functions. (leg, wing, fin) Analogous structures have similar functions but differ in anatomy and did not derive from the same ancestral structure (insect wing and bird wing)

Anatomical Evidence Flightless birds have wings. Vestigial structures are reduced and functionless anatomical features Flightless birds have wings. Snakes rear limb spurs. Humans have a tail bone.

Anatomical Evidence Related species share embryological development.

Biochemical Evidence Almost all living organisms use the same basic biochemicals: DNA, ATP, same enzymes, DNA triplet code, 20 amino acids…

Biochemical Evidence Similarity of biochemistry is explained by descent from common ancestor. Organisms show less difference in their DNA the more closely related they are: 2.5% difference between humans & chimpanzees 42% difference between humans & lemurs.

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