Natural Selection“Survival of the Fittest”PAST PRESENT

Phenotype vs. Genotype• Natural selection

acts on ________ rather than _________.

• Those best suited for their environment will ________ (taller giraffes).

• Those least suited for their environment ___ faster and leave ________ offspring (short giraffes).

PAST PRESENTphenotype

genotype

survive

die

fewerTt tt tt tt Tt tt tt TT

Genetic variation is essential!

• ________ promote genetic variation, which helps ensure a species survival. Therefore, mutations are NATURAL and INCREASE genetic diversity

• Reproduction(Crossing over) promotes genetic variation which helps to ensure a species survival

Mutations

Adaptation

Some phenotypic feature or trait that improves an organism’s likelihood of survival and reproduction

How might this adaptation have occurred and how is it beneficial? What would you expect to happen to the deer population in the next 1000 years?

In Georgia, there is a popular hunting area of forest, where the hearing-deer live. This species of deer has 6 ears.

Differential survival of groups of organisms (who is going to live?)

1.Those groups of organisms who are best adapted (fittest) to their environment will survive, while the

least adapted will eventually die out (differential survival).

2. Those that survive get to reproduce

3.The trait MUST be genetic to be passed on to next generation.

Changing Environments

•When the environment changes, those •who are now fittest will survive and repopulate.

•Why is it important for a species to have variation?

Which rabbit will survive better here?

What about here?

Charles Darwin

• 1st credited with theory of Evolution– Wrote the Origin of Species

• Book based on his observations during trip to Galapagos. Made detailed sketches and notes to record observations.

Prezygotic and Postzygotic barriers

• Geographic isolation – organisms, originally of same species (in same area) got physically separated and were no longer able to mate

• Reproductive Isolation – organisms become genetically incompatible or offspring are not viable or offspring are not fertile.

Squirrel A and B live on opposite sides of the Grand Canyon. Even though they are different species, don’t they look similar?

Geographic Isolation

Reproductive Isolation

X

mule

Speciation=process of new species formation, typically due to a favoring of certain traits.

Sp

eciation