Atavism

Atavism, also known as reversion, is the sudden reappearance of a certain ancestral but not parental structure which has either completely disappeared or greatly reduced.

• Rudimentary tail in newborn babies.
• Movable pinna (external ear that can be moved using muscles).
• Large and prominent canines.
• Very long and dense body hair.
• Additional mammae (extra nipples/mammary structures).

A-D. Some atavistic structures in human: A. a rudimentary tail in a newborn baby; B. large canines; C. long and dense hairs on the body; D. additional mammae (nipples)

• Atavism shows that present-day organisms retain ancestral genetic information.
• Reappearance of ancestral traits is considered evidence of evolution because it indicates descent from earlier forms with different characteristics.

• Atavism (reversion) is the sudden reappearance of an ancestral trait that had disappeared or become greatly reduced in previous generations.
• The trait shown in atavism is ancestral, not a usual visible character of the immediate parents.
• Human examples of atavism include a rudimentary tail in newborns, movable pinna, large canines, very long and dense body hair, and additional mammae.
• Atavism is considered an important evidence of evolution because it shows that present-day organisms still carry ancestral genetic information.