Evolution

Chapter 7 and 8

Theory of Evolution

• Process by which populations accumulate inherited changes over time

• Change over time

What is a Theory?

• An explanation for an observation or a series of observations that is supported by a considerable body of evidence.

Evidence of Evolution

• Fossil Record• Vestigial Structures• Comparing Organisms

• Skeletal Structures• DNA• Embryonic Stages

Fossil Record

• Fossils are the remains or imprints of once-living organisms found in the layers of the Earth’s crust

• Fossil provide a sequence of evolutionary events known as the fossil record

Vestigial Structures

• Remnants of once useful structures

• Example – Modern whales do not have legs, however they do have remnants of hind limb bones

• Modern Boa Constrictors also have remnant legs

Evolution of Whaleshttp://www.pbs.org/wgbh/evolution/library/03/4/l_034_05.html

Comparing Organisms

Charles Darwin• Darwin was a naturalist

(scientist who studies nature)

• He collected samples and learned about the world on his Voyage of the Beagle

Darwin’s Finches and the Galapagos Islands

• Darwin’s most famous encounter was on the Galapagos where he observed animals and plants that were very similar, yet showed great variation

Historical Contributions• Darwin lived during a time of great discovery • Scientist soon realized that the earth was very old, old

enough for great changes to have occurred

• Thomas Malthus observed that if populations continue to grow, at some point there will be insufficient resources, food and living space

Hutton Lyell

Change Over Time

• Darwin began developing his theory in 1836, but he did not publish until 1858 out of fear

• It took the discoveries of Alfred Wallace to encourage Darwin to publish is work “On the Origin of Species”

Natural Selection

1. Overproduction – Species produce more offspring than can survive to maturity

2. Variation – Individuals in a population have slight differences. Some traits will increase that an individual will survive to reproduce

3. Struggle to Survive – Not enough resources to support all individuals Competition

4. Successful Reproduction – Individuals who are best adapted to survive and reproduce Reproducing more of their successful trait

Speciation

• If two groups become separated and have unique environmental pressures, overtime the two populations can become so different that they can no longer interbreed

• Species that cannot interbreed are considered different species

Separation