EVOLUTION Chapter 15

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Evolution

time - change over •

Theory

– a well-supported testable explanation of phenomena in the natural world

Charles Darwin

The variety of living things…

BIOLOGICAL DIVERSITY

Darwin found a huge variety of living things, each well adapted to their environment

Voyage of the Beagle 1831

Patterns of Diversity • Visited Argentina and Australia similar grassland ecosystems – those grasslands were inhabited by very different animals.

• Patterns of Diversity Darwin asked questions… – Why no rabbits in Australia, despite the presence of habitats that seemed perfect for them?

– Why no kangaroos in England?

Living Organisms and Fossils • Darwin collected the preserved remains of ancient organisms,

fossils

. • Some of the fossils resembled organisms that were still alive today.

Living Organisms and Fossils Others looked completely unlike any creature he had ever seen. • As Darwin studied fossils, new questions arose. – Why had so many of these species disappeared? – How were they related to living species?

The Galapagos Islands • The smallest, lowest islands were hot, dry, and nearly barren-Hood Island-sparse vegetation • The higher islands had greater rainfall and a different assortment of plants and animals-Isabela- Island had rich vegetation.

The Galapagos Islands • The shape of a tortoise's shell could be used to identify which island a particular tortoise inhabited.

More Galapagos Animals

The Journey Home • Darwin Observed that characteristics of many plants and animals vary greatly among the islands • Hypothesis: Separate species may have arose from an original ancestor

Ideas that shaped Darwin’s Thinking • •

James Hutton:

1795 Theory of Geological change – Forces change earth’s surface – Changes are slow – Earth much older than thousands of years

Ideas that Shaped Darwin’s Thinking • • •

Charles Lyell

Geographical features can be built up/torn down Darwin thought if earth changed over time, what about life?

• Lamarck’s Theory of Evolution Tendency toward Perfection (Giraffe necks) • • Use and Disuse Theory of Acquired Traits (characteristics)

Population Growth • • Thomas Malthus English economist If population grew… – Insufficient living space – Food runs out – Darwin applied theory to animals and plants

Publication of On the Origin of Species • 1859 after 25 years of study, thought, struggle • It outlined his theories of natural selection and evolution over time

His Studies of Variation • • • • Darwin didn’t know about genes He DID observe traits being passed to offspring He knew about Artificial Selection – nature provides variation, humans select variations they find useful Dogs, pigeons, crops, horses, cows

Natural Selection • • • There is a struggle for existence…living things need food, living space Some individuals are better their environment

adapted

for Adaptation – any inherited characteristic that increases an organism’s chance of survival

SURVIVAL OF THE FITTEST

Can you think of any adaptations?

• Check out these examples of adaptations

• Descent with Modification Darwin proposed that living things changed over long periods of time because of natural selection • • • • It implies that all living organisms are related Living things evolved from a common ancestor Common Descent Tree of Life links all living things

Evidence of Evolution • Fossil Record • Geographic Distribution of living things • Homologous structures • Vestigial organs • Similarities in embryology

Geographic Distribution of Living Things • • Darwin found different species of animals on different continents He recalled similar environments and sometimes similarities in different animals

• • • Homologous Structures have different mature forms but develop from same embryonic tissues Vestigial organs are traces of homologous organs Ex. Legs in skinks (p. 385)

Similarities in Embryology Similar in early stages…common ancestry?