A De-Volution or Atavism occurs rarely, many cases are spread throughout the world that a human baby born with a "Vestigial Tail". A extended vestigial bone often refers as "coccygeal process".
In this process an ancestral genetic trait reappears after having been lost through evolutionary change in previous generations.
Every living creature on this planet posses "phenotypic" features inside their DNA these traits are often locked due to the Evolution that's been started since 3.4 billion years ago. Due to evolution we have seen many physical and chemical changes in humans, animals and plants.
The evolution occurs through a natural selection here comes "GoD" who decides what's best for every living thing on Earth and he is been deciding since the beginning of time but some of us never listen, never learn that if nature decides to exterminate, hide or secretly lock something its for the our best.
The saying of "curiosity killed the cat" originated in 1598 in a play that was written by Ben Johnson and adapted to by William Shakespeare.
This saying perfectly apply on us, Humans
Because we are eager to find out secrets and when we do tend to play "GOD"...