Horse Natural Selection (ID)

“Natural selection is the gradual, nonrandom process by which biological traits become either more or less common in a population as a function of differential reproduction of their bearers. It is a key mechanism of evolution.” Also known as survival of the fittest. The horse family known as the equidae first emerged in North America 55 million years ago and has evolved over time. Nearly all of these diverse horses extinct over time. In this present day the equidae family, which also included zebras and donkeys, only has seven different species. 35 million years ago the climate began to change the wet forests in North America to dry grasslands. This change affected horse evolution. Present day horses show many adaptations to the plains habitat. I.E.- Early horses had 3 or 4 toes, each ending in a small hoof. But those horses with bigger stronger, middle toes were better adapted to run on and walk on dry, hard ground. Natural selection led to the near disappearance of the side toes, while the middle toe and its hoof became gradually bigger.