Yo! Please get out your Natural Selection outline you made from the textbook – we’re going to add to it.

Didn’t do it? Get out a piece of paper.

Everyone – please read the board.

Please pass back the permission slip!

Armand Bayou Nature Center

Natural Selection

Natural Selection – Process by which organisms best suited to

their environmental conditions are most likely to survive and reproduce

It’s HOW evolution works!

Three conditions that must be true for natural selection to occur: Natural variation of a

trait in a population Trait must be heritable Trait must lead to

differential reproduction (must make you more likely to reproduce)

Some male peacocks have more vibrant tail displays than others

Tail and display behavior is encoded in DNA

Males with more vibrant displays are more likely to mate.

Natural selection leads to adaptations Adaptation: a structure

or behavior that helps an organism survive in their environment.

Through natural selection, adaptations are encoded in DNA. An INDIVIDUAL cannot change their

adaptations. POPULATIONS undergo natural selection

and over many generations, can experience a change in adaptations.

Some people confuse adaptation with acclimation!

Coevolution Read the excerpt from the text, then draw a

cartoon of the steps of coevolution.

Speciation

Speciation How do new species evolve?

Divergent selection – in ancestral species, variation provides ability to survive in different environments.

If different groups of the species become physically isolated, they can continue to adapt to separate environments (microevolution)

Eventually, they may be so different that they cannot successfully mate = new species.

Geographic Isolation

So what if an entire species can’t change quickly enough to deal with changing conditions?

For each individual, either it survives to reproduce or it dies

So what if an entire species can’t change quickly enough to deal with changing conditions?

Extinction Background extinction

rate: about 1 to 5 species/ year

Mass extinction: the loss of many species in a sudden event.

Current extinction rate: 1,000 to 10,000 times the natural background rate (dozens a day).

Legal/scientific designations Healthy Threatened Endangered Extinct

Grizzlies and Polar Bears diverged about 150,000 yrs ago.

Check for understanding! Why can’t an individual change it’s

adaptations in its lifetime? What is the better word for an inidividual

getting used to a new situation? What happens to populations in which no

individual is able to survive?