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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?
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