NATURAL SELECTION

Hutton, Lyell, Lamarck and Malthus

The ideas that shaped Darwin…

Evidence of a Changing Earth

Scientists Hutton and Lyell studied the organisms found in fossils.

The older the fossil, the deeper it was buried

Changes in the appearance of the organisms could be seen between layers.

Lamarck’s Evolution Hypothesis

In 1809, Lamarck proposed that an animal’s behavior could change the traits passed down to their babies.

He thought, the more you use it, the more it grows.

He did not know about how genes were passed down.

Malthus’ Population Growth

Population growth is limited by the resources available, such as food and living space.

Once the food or the space starts to run out, then the growth rate will have to slow and then stop.

Darwin’s Work

Inherited Variation

Slight mutations in the genetic code happen

Before Darwin, scientists did not think this was important

Darwin claimed that differences matter and can change the direction of a species

Artificial Selection

Nature provides genetic variation

Humans often select for traits that they find most useful.

Example: We like larger, sweeter tomatoes, so we will selectively breed plants for those traits.

Struggle for Existence

Species have to compete for the best food, living space and mates

This drives the selection process

Survival of the Fittest

Organisms with the best adaptations for the environment will survive.

These adaptations are passed down through the genes from parents to babies.

The others will die off. Darwin called this,

“Natural Selection.”

Evidence for Evolution

The Fossil Record

There are many marine life fossils

They saw many species with shells

The shells got increasingly complex, suggesting evolution took place over time

Homologous Body Structures

Same bones, but different uses

Mammal Examples: Human Arm

w/Hand Horse Leg w/Hoof Whale Flipper Bat Wing

Similarities in Embryos

Types of Selection

Directional Selection

Individuals at one end of the curve are better fitted for the situation, so all shift.

Stabilizing Selection

Individuals in the middle of the curve are best fitted for the situation, so ends drop off.

Disruptive Selection

Individuals at either extreme are better fitted for the situation than an average individual.

Genetic Drift

Certain traits many become more common in a population by chance, rather than by a type of purposeful selection.

Hardy-Weinberg Principle

There are 5 was to have a population at equilibrium (where there is no change)

1. Random Mating

2. Large Population

3. No Movement into or out of the population

4. No Mutations

5. No Natural Selection

The Process of Speciation

Reproductive Isolation

Only individuals of the same species can mate

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Behavioral Isolation

Individuals could breed, but their styles of behavior or courtship make them not attracted to one another.

Geographic Isolation

Individuals could mate, but they are separated by distance

Temporal Isolation

Individuals could mate, but they naturally mate at different time periods.

Process for the Evolution of Darwin’s Finches

How Speciation Occurred…

Founders Arrive: A few finches flew to one of the islands from South America and mated

Separation of Populations: Some of these finches flew to a neighboring island

Changes in Gene Pool: Adapting to new island Reproductive Isolation: Now the finches on the

different islands are too different to mate! Ecological Competition: need food & nests Continued Evolution: natural selection continues

Patterns of Macro-Evolution

Extinction

Species that cannot adapt to their environment will die out.

Adaptive Radiation

Many species evolve from a single species

Convergent Evolution

Some species look similar

However, they are not closely related genetically

Similar environmental factors cause the species to evolve in similar ways.

Beaver

Coypu

Coevolution

The process when two species evolve in response to changes in each other over time

Example: Flowers change to keep attracting the bees needed to pollinate them.