Charles Darwin An English Naturalist – studied animals and their environment how different species interact with their environment Natural selection is the basis for the modern evolutionary theory 5 year voyage on the HMS Beagle studied and collected biological specimens at every port

Voyage of the HMS Beagle Many species of plants and animals that were similar to those found on the main land Species can change over time

Thomas Malthus Economist – essay on the principals of population Alfred Wallace Biologist – Came to similar conclusions as Darwin and presented their findings to the scientific community Human population grow Faster than earth’s food supply

What kinds of struggle are there? Competing for living space Competing for food Escape from predators Finding a mate Finding shelter What individuals do you think would survive to produce offspring? Strongest SmartestHealthiest Those most likely to survive the struggle for survival

Evolution By Natural Selection

Natural Selection A mechanism for change in a population Organisms with variations that aid in survival, reproduce, and pass their variations to the next generation Organisms without these favorable variations are less likely to survive and reproduce Subsequent generation consists largely of offspring from parents with the favorable variations

What are some variations?  Traits that vary  Skin or coat color  Eye color  Size of body or parts of body like tail, beak, claw or antlers

What is the source of variation in traits or characteristics?  Arise by Genetic Mutation  Build up on Existing Traits

How are these traits passed on to the generations that follow?

Sometimes we use this natural variation  Largest Hogs  Fastest Horses  Best hunting dogs  Cows that produce the most milk

Artificial Selection Occurs when nature provides variation among different organisms and humans select the variations they find useful

Natural Selection Sometimes the environment acts as a selective agent by favoring individuals in the population that have a certain trait (like a specific color).

The bird prefer the green beetles over the orange ones. As the birds select only the green beetles to eat the percentage of available green beetles decreases. After many generations, the population has changed and green beetles are rare.

Case of the Peppered Moth  England, late 1800s (Industrial Revolution period)  The gene for DARK is dominant over light  At one time light-colored forms of the moth were most common  Over a 50 year period, the dark form became the most common

Case of the Peppered Moth Biologists hypothesized that this was an adaptive shift in response to a changing environment Increased burning of coal during the Industrial Revolution had led to high levels of air pollution that killed the pale-colored lichens (tree moss) growing on tree trunks

Case of the Peppered Moth The tree trunks, which previously appeared to be a light, scaly color from the lichens, became very dark Tree trunk color is important to the survival of moths. Moths rest on tree trunks during the day Birds, their primary enemies, mostly eat varieties that are easy to find. Thus the light form of this moth became rare

Light Peppered Moth Light- colored peppered moth on a tree with a lichen

Light Peppered Moth Light- colored peppered moth on a tree covered with soot

Dark Peppered Moth Dark- colored peppered moth on a tree covered with lichen

Darwin describes natural selection as Fitness - the ability of an organism to survive and reproduce in its specific environment

Natural Selection Cannot be seen directly Takes place over many generations No human influence Natural Selection Natural Selection increases the number of individuals with the beneficial trait, so the characteristics of a population change over time