5.6 Speciation (allopatric), Rate of Evolution and Macroevolution

Allopatric Speciation:
Allopatric Speciation occurs when a species is split or divided into two groups.
Allopatric Speciation consists of three steps:
1. A physical barrier: a species accepting a new environment.
2. Natural selection: works on both populations.
3. A new species which no longer can breed with its ancestral species.

For example: Bears.
The polar bear and grizzly bear both come from a common ancestor. But because they now live in different environments, have gone through some type of mutation (natural selection) they can no longer breed together.

 

"Speciation." Biology. Ed. Richard Robinson. New York: Macmillan Reference USA, 2009. Gale Science In Context. Web. 21 Apr. 2011.

 

Rate of Evolution:

Theory of Gradualism:

"The theory that evolution occurs gradually over millions and millions of years"

Example: When Darwin first proposed his evolution theories, he believed that evolution happened with small bits at a time, the Theory of Gradualism.

Theory of Punctuated Equilibrium:

An evolutionary theory created by Niles Eldredge (1943-) and Stephen Gould (1941-2002).

The Theory of Punctuated Equilibrium states that there are long periods in time at which evolution does not happen. Then, many evolutionary changes happen within short periods of time. The theory suggests that new species have risen very rapidly within the time frame of only a few thousand years, and then remained unchanged for millions of years after their rise.

 

"Gradualism." World of Biology. Gale, 2006. Gale Science In Context. Web. 21 Apr. 2011.

 

Macroevolution:

"[Goldschmidt] believed that the overall pattern of chromosomes and the chemical configuration of the chromosome molecule determine heredity, rather than the qualities of individual genes that make up the chromosomes."

Richard B. Goldschmidt theorized that macroevolution was where large mutations occured, therefore creating new species.

Divergent evolution:

Where plant or animal characteristics that share an evolutionary origin become distinct over time (millions-billions of years).

Example:

Human arm and bats wing. (Sound familiar? Related to homogenous features)

 

"For humans, upright walking on the ground required alterations in the foot for better speed and balance. The whale and bat modified the ancestral structure in response to environmental pressures of their own. These differing traits soon became characteristics that evolved to permit movement over the ground and in the water and air."

 

"Richard B. Goldshmmidt." World of Genetics. Gale, 2006. Gale Science In Context. Web. 21 Apr. 2011.

"Evolution, divergent." The Gale Encyclopedia of Science. Ed. K. Lee Lerner and Brenda Wilmoth Lerner. 4th ed. Detroit: Gale, 2008. Gale Science In Context. Web. 21 Apr. 2011.