Species • What is a species? A species is defined as a group of organism that can interbreed and create fertile offspring. Are a Dotson and a Chiwawa the same species? What about a wolf and a Chiwawa? A zebra and a horse? A Mule and a Donkey?
Other Mechanisms • Artificial selection • Humans choosing traits we want and selectively breeding them into a species • Natural Selection (modern) • Stabilizing Selection • Eliminates Extreme expressions of a trait when the average leads to higher “fitness” • Example: Human Birth Weight
Directional Selection Extreme selection favored. • Example: Peppered Moth
More Mechanisms • Disruptive Selection • Splits populations into 2 groups, removing average.
Sexual Selection • Exists when males and females differ greatly • Example - Peacocks
Reproductive Isolation • Prezygotic Isolation • Pre Fertilization • Geographical, ecological, behavioral • Eastern/Western Meadowlarks • Orchids • PostzygoticIsolation • After Fertilization • Prevent survival or infertility • Mule, Liger, Zorse