a group of organisms that look alike and can interbreed to produce fertile offspring in nature.

• The evolution of new species, a process called

speciation.

-But HOW are new species made?

SPECIATION• What is a species?

Tree Kangaroo! ->

• In nature, physical barriers can break large populations into smaller ones.

• Geographic isolation occurs whenever a physical barrier divides a population.

• A new species can evolve when a population has been

geographically isolated.

SPECIATION

• When geographic isolation divides a population of tree frogs, the individuals no longer mate across populations.

• Tree frogs are a single population.

SPECIATION

• The formation of a river may divide the frogs into two populations.

SPECIATION

• Over time, the divided populations may become two species that may no longer interbreed, even if reunited.

SPECIATION

• Reproductive isolation occurs when formerly interbreeding organisms can no longer mate and produce fertile offspring.

SPECIATION

• For example, if one type of tree frog mates in the fall and the other mates in the

summer, these two populations will not mate with each other and are reproductively isolated.

DIVERSITY

• Divergent evolution is the pattern of evolution in which species that were once similar to an ancestral species diverge, or become increasingly different.

• Divergent evolution occurs when populations change as they adapt to different environmental conditions, eventually resulting in new species.

Possible AncestralLasan finch

Amakihi Extinct mamo

Crestedhoneycreeper

Akialoa

Akepa

Akiapolaau LiwiMaui parrotbill

Apapane

Ou

Grosbeak finch

PalilaAkikiki

Niihau

Kauai

Oahu

Lanai

Molokai

Maui

KahoolaweHawaii

• When an ancestral species evolves into an array of species to fit a number of diverse habitats, the result is called adaptive radiation.

• A pattern of evolution in which distantly-related organisms evolve similar traits is called convergent evolution.

• Convergent evolution occurs when unrelated species occupy similar environments in different parts of the world.

DIVERSITY

Which type of natural selection does NOT favor the evolution of new species?

Question 1

D. directional

C. stabilizing

B. disruptive

A. divergent

The answer is C. Stabilizing selection reduces variation in a population.

Which of the following rarely affects a population’s genetic equilibrium?

Question 2

D. disruptive selection

C. gene flow

B. lethal mutations

A. beneficial mutations

The answer is B. Organisms with lethal mutations do not survive. Therefore, organisms with lethal mutations cannot produce enough offspring to affect a population’s genetic equilibrium.

Why are the Galapagos Islands rich in unique species of organisms?

Question 4

D. The island species have been subjected to stabilizing selection.

C. Lots of species constantly move in and out of the islands.

B. The islands are geographically isolated.

A. The islands have an abnormal number of mutations.

The answer is B. Geographic isolation has helped to keep the islands’ species unique.