Descent With Modification

Chapter 22

Historical Context

• Darwin 1st to propose idea of natural selection.

• Wrote The Origin of Species.• After natural theology

(Creationism), creation of taxonomy (system of naming organisms)

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• 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.

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• Lyell – uniformitarianism -geological processes not changed throughout history.

• 1809 - 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.

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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)

• 1st major point of ideas - descent with modification - all creatures share common ancestor.

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• Organisms developed characteristics to adapt to surroundings.

• Closer related species are, more recent their common ancestor.

Copyright © 2002 Pearson Education, Inc., publishing as Benjamin CummingsFig. 22.7

•This evolutionary tree of the elephant family is based on evidence from fossils.

• Developed theory of natural selection.

• Observations based on ideas:• 1All organisms have potential to

have many offspring; something must limit number.

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• 2Populations of organisms tend to remain steady in size over time.

• 3Environmental resources limited.• Inference #1 - too many offspring

produced - struggle to survive occurs - certain number of offspring will survive.

http://savinganimals.smugmug.com/keyword/dogs#36007645

• 4No 2 individuals in population alike.

• 5Differences are inherited.

• Inference #2 – Survival depends on heritable differences.

• Inference #3 – Favorable characteristics – survive - more offspring with favorable characteristics.

http://evolution.berkeley.edu/evosite/evo101/images/vert_tree.gif

• Main points:• 1Natural selection - unequal ability

of species to survive and reproduce.

• 2Based on ability to interact, adapt to environment.

• 3Based 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. 22.10

• 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.

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

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• Darwinian view on life:• 1Diversity comes from descent

with modification from ancestral species.

• 2Modification - result of natural selection over long period of time.

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• Population, not individual, evolves.

• Natural selection involves changes between individual and environment - ultimately population that evolves.

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• 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.

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• 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.

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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. 22.12

• 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.

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• 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.

http://www.answersingenesis.org/home/area/magazines/tj/images/v14n2_vestigial_structures.gif

• 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.