Why a person has five fingers on their hands and legs?
In fact, such a number of fingers is characteristic not only for a person. This primitive, the initial structure of the limb is characteristic of all ground vertebrates. People have five fingers on their hands and legs, because the same has been our ancient monkey-like ancestors. They inherited such a number from their ancestors and so on, up to amphibians inhabited by the Earth more than 300 million years ago.
The five-pack limb does not have special advantages over the limb with another fingers: for example, four or six. Scientists believe that the five-capness of most types of vertebrates, including a person, has consolidated in the process of evolution. It was quite "lucky", for example, octal amphibians, and then we could have eight fingers.
However, there were exceptions. For example, the horses due to the disappearance of four fingers of five decreased area support of the limbs, which became one of the devices to high-speed movement. The ancestors of a person "extra" fingers did not find out, so everything was preserved.
It happens that vertebrates on one limb are "additional" fingers, but it is rather an exception. For example, Ernest Hemingway has all cats with polydactile, and their multiple descendants still live on the territory of the Museum of the Writer in Ki-West (Florida). Most of them have six, seven, and some even have eight fingers. American Genetic Sewal Wright once brought a guinea pig with 44 fingers on all four paws. True, she did not live for a long time.
There are failures and people. Current fingers with additional fingers are born one person out of 3,000, Africans have one of 300. And the latter usually doubles the little finger, and Europeans have a thumb. Although theoretically "optional" can be any.
As a rule, polydactyl is a genetic anomaly. And due to the fact that it is transmitted on the dominant type, in some families it is found in many generations. So, the French naturalist Pierre Moro de Moperty described the inheritance of the polydactilia at the ancestors and descendants of one Berlin doctor, the grandmother was six fingers on her hand and leg. So much passed his mother, and then he himself and two of his five children. There are more impressive pedigrees with polydactile. For example, a case is described when multiplying traced over six generations.