Darwin’s Theory of Evolution

Biology OneChapter 16

I. Darwin & his voyagesA. General info

1. evolution = change over time*a. process by which modern

organisms descended from ancient speciesb. it’s a well supported theoryabout the diversity of organisms

*1) testable explanation of natural phenomena

B. Charles Darwin (2/12/1809 – 4/19/1882)

1. British naturalist2. worked/traveled on HMS Beagle

a. 1831-1836b. sailed around worldc. collected biological & fossil specimens

1) known for work in the Galapagos

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Beagle’s 2nd voyage

HMS Beagle

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Map of Galapagos Islands. Some of these islands are very, very dry, and there is not much vegetation to eat. On those islands, cactus "trees" are a good source of dinner for tortoises.

3. Darwin observed:a. many unique species w/

similarities to othersb. species seemed well suited

for their environmentsc. some species lived one place

but not another even though habitats were similard. many fossils of species that

had disappeared but were related to living forms

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 "The black Lava rocks on the beach are frequented by large (2-3 ft) most disgusting clumsy Lizards. They are as black as the porous rocks over which they crawl & seek their prey from the Sea. Somebody calls them 'imps of darkness'. They assuredly well become the land they inhabit.”

~Charles Darwin, diary entryMarine iguanas

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Galapagos tortoises – Different shell shapes & necks due to differences in habitat & diet

Some of the 14 speciesof finches Darwin cataloged;they differ in beak, talons, coloring, etc.

e. Noticed animal & plant species varied among different islands

1) had they once been the same?2) did they evolve from an original

South American ancestor?3) what led to the changes?

II. Ideas that influenced DarwinA. Common ideas in Darwin’s time

1. Earth & life were only a few thousand years old

2. current species had not changed from original forms

3. rocks & geological features were due to sudden catastrophicevents rarely witnessed

B. Ancient, changing Earth? 1. James Hutton (1795)

a. proposed Earth may be millions of years old

2. Charles Lyella. can use current world observations to explain how Earth’s features changed over

long times

3. Jean-Baptiste Lamarcka. believed use/disuse of organs led

to traits that could be passed to offspring

b. incorrect – behavior doesn’t effect heredity

1) Led to study of evolution4. Thomas Malthus (economist)

a. believed if human population grew unchecked, would run out of food, living space

III. Darwin’s BookA. On the Origin of Species by Means of Natural Selection

1. published in 18592. several key ideas on natural selection

B. Natural selection ideas1. variation among organisms is important

a. Darwin bred pigeons to test this2. organisms struggle for existence

a. compete w/ others for food, habitat, mate, etc.

b. knew some organisms had advantages over others

1) ex: speed, camouflage, strength

3. some organisms have fitness adaptations

a. inherited characteristic that increases chances of survival1) may be anatomicala) ex: porcupine quills, long neck2) may be physiological a) ex: hunting behaviors, speed

b. Led to idea of survival of the fittest1) individuals better adapted to

their environments survive, reproduce & pass adaptations to offspring

2) a.k.a. natural selection3) occurs w/out human control4) over time, results in better fitness

of a species to its environment

05/09/2017 C. Descent with modification1. each living species developed from

but differs from older speciesa. implies relationships between all living organismsb. ex: common ancestor for birds &

reptiles2. led to principle of common descent

a. all species, living & extinct, were derived from common ancestors

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Archaeopteryx:Common ancestor of birds & reptiles?

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The central ideas of evolution are that life has a history — it has changed over time — and that different species share common ancestors.

D. Evidence of Evolution1. The Fossil Record

a. fossils = preserved remains of ancient organisms

b. helped provide evidence for age of Earth

c. can compare/contrast ancient & modern organisms

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d. Many gaps exist in between various stages of evolution1) some transitional fossils have been found

a) show intermediate forms between modern & ancient species

Tiktaaliktransitional fossil ex.

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Horseshoe crab; late Jurassic

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Brittlestar;lower

Devonian

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Bat;Eocene

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Shark;Middle Cretaceous

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Isopod in amber;Pliocene to Pleistocene

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Fossil of a 26-inch fish-like vertebrate believed to be at least 560 million years old; believed to be oldest vertebrate fossil.Discovered in sandstone in Flinders Ranges in South Australia, 2003.

2. Geographic distributiona. similar species were found in different parts of the world

1) could have descended w/ modification from a common ancestorb. similar habitats often supported different species but w/ similar features

1) faced same natural selection pressures

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3. Homologous body structures exist in many organisms

a. from same embryonic tissuesb. similar in functionc. adapted to better suit conditionsd. may develop as vestigial organs

1) have little/no function in current species

2) shows relation to other species

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Vestigial organs

4. Embryology can point to common ancestor

a. early development stages show similar tissue patterns

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E. Summarizing Darwin’s ideas1. organisms differ, & some is genetic2. more offspring are produced than can survive3. there is competition for limited resources4. natural selection leads to changes in species over time

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5. Species today have descended with modification from a common ancestora. a single tree of life unites all organisms

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