Among humans, we occasionally see children with short tails, people with long hair, women with many nipples and so on. These phenomena indicate that human ancestors may be animals with tails, long hair and many nipples. So atavism is also a kind of evidence of biological evolution.
Extended data
The human example—
For example, a hairy child with hair on his body is an atavistic "degeneration" phenomenon of human hair tissues and organs, and a person with naturally rotating ears can be classified as an atavistic "degeneration" phenomenon of the nervous system, and a person with naturally tail can be classified as an atavistic "degeneration" phenomenon of degenerated organs. Therefore, the location of atavism is uncertain.
1977 On September 30th, a young boy was born in a farmer's house in Liaoning. Except his hands, feet, palms and lips, his body is covered with different lengths of hair. These hairs are darker and longer than those of ordinary people, much like the ancestors of human beings-apes. What appears in this young man is atavism.