Descent With Modification Chapter 22

Historical Context Darwin 1 st to propose idea of natural selection. Wrote The Origin of Species. After natural theology (Creationism), creation of taxonomy (system of naming organisms)

Darwin’s views influenced by fossils, impressions of organisms from past and other researchers. Strata (layers) of rock held fossils dated from youngest (towards top layer) to oldest.

Study of fossils (paleontology) supported idea that change had happened. Cuvier – catastrophism - large floods occurred between layers of rock - new species repopulate devastated area.

Lyell – uniformitarianism -geological processes not changed throughout history Lamarck - theory of evolution based on observations of fossil invertebrates.

Use and disuse of parts and inheritance of acquired characteristics important in theory. No evidence that acquired characteristics inherited.

Darwinian Revolution Darwin set sail on The Beagle - discover coastlines of South America and to chart out South American coastlines. Collected specimens - noticed they differed between various parts of the world.

Origin of new species and adaptation of species to environment closely related processes. Finches on Galapagos Islands differed in beak sizes according to what they ate.

Darwin wrote The Origin of Species. Outlined ideas on evolution and natural selection (Darwinism) 1 st major point of ideas - descent with modification - all creatures share common ancestor.

Organisms developed characteristics to adapt to surroundings. Closer related species are, more recent their common ancestor.

Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Fig This evolutionary tree of the elephant family is based on evidence from fossils.

Developed theory of natural selection. Observations based on ideas: 1 All organisms have potential to have many offspring; something must limit number.

2 Populations of organisms tend to remain steady in size over time. 3 Environmental resources limited. Inference #1 - too many offspring produced - struggle to survive occurs - certain number of offspring will survive.

4 No 2 individuals in population alike. 5 Differences are inherited.

Inference #2 – Survival depends on heritable differences. Inference #3 – Favorable characteristics – survive - more offspring with favorable characteristics.

Main points: 1 Natural selection - unequal ability of species to survive and reproduce. 2 Based on ability to interact, adapt to environment. 3 Based on ability for characteristics to be passed.

For example, these related species of insects called mantids have diverse shapes and colors that evolved in different environments. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Fig

Thomas Malthus noticed humans produce quicker than resources. Certain inherited characteristics allow certain members of population to survive such conditions.

Differential reproduction - passing on of favorable traits to offspring. Traits become more dominant in population over time - evolution.

Artificial selection - organisms with favorable traits selected to mate with others like them - increases frequency of traits in population (breeding).

Darwinian view on life: 1 Diversity comes from descent with modification from ancestral species. 2 Modification - result of natural selection over long period of time.

Population, not individual, evolves. Natural selection involves changes between individual and environment - ultimately population that evolves.

Population - group of interbreeding individuals of single species that share common geographic area. Evolution measures change in relative proportions of heritable variation in population over succession of generations.

Evolution increase or decrease inherited traits, not individual traits that person may have acquired over lifetime. Natural selection situational. Some traits are helpful in one environment; not helpful in other.

Examples of natural selection Insects - resistant to insecticides. Those survived insecticide survived to pass gene on. Result - immunity to certain pesticides.

Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Fig

Natural selection favors characteristics in variable population that fit current, local environment. Drug resistance - evolution has occurred. Drug-resistant strains evolve rapidly in HIV population, making drug treatment difficult.

Other evidence Evidence of gradual change throughout fossil history. New species evolve by modifications as populations adapt to new environments. Similarity in characteristics resulting from common ancestry - homology.

Anatomical similarities among species - wing of bird, arm of human - different functions, similar anatomy. Forelimbs of human, cats, whales, bats share same skeletal elements - homologous structures.

Study of comparing similar structures - comparative anatomy. Vestigial organs do not have any importance to current organism, had important functions in ancestors. Some snakes - have pelvic, leg bones.

Darwin studied biogeography - led to evolution. Species that lived close tended to be more similar than species that lived further away. Sugar glider, flying squirrel adapted to same mode of life - not closely related.

Like a marsupial mammal Like a placental mammal

Islands show strong evidence for evolution - many species of plants and animals that are endemic (found nowhere else in world)

Why is it a theory? Those who dismiss Darwin’s theory unable to separate main parts of theory. Natural selection well accepted - can be tested and proved.