How Different Species Arise

What is a species? A group of organisms that can interbreed and produce fertile offspring in nature. New species arise through the process of speciation.

Divergent Evolution When one species evolves into two or more species with different characteristics.

Geographic Isolation Occurs when a population is separated by something like a river, canyon, mountain, etc.

Geographic Isolation (cont.) - If the two areas have different conditions, then different variations will be selected for. - The gene pools of the two groups may then differ greatly and become separate species. Darwin’s finches

Reproductive Isolation When two similar or related species come together they may not be able to interbreed. Can be caused by different mating habits the sperm may not be able to fertilize the eggs chromosome numbers may not match up etc.

Genetic Drift If a portion of a population is lost (volcanic eruption, flood, destruction by humans, etc) and only a small number of individuals remain, there will be less genetic diversity. In other words, the gene pool has been reduced. If the alleles that were lost were of adaptive value, then the species may become endangered.

Genetic Drift (defined) Caused by rapid changes in the numbers and kinds of genes in a small, isolated population

Speciation by Polyploidy Organisms have to have the same ploidy ( number of chromosomes) to reproduce.

Sympatric Speciation New species can be produced by behavioral adaptations such as choice of food, time of mating or emergence.