The definition of an atavism is a genetic trait that reoccurs after skipping several generations.(noun)
If a person has blue eyes like her great great grandmother but her mother, grandmother, and great grandmother have brown eyes, then having blue eyes is an example of an atavism.
See atavism in Webster's New World College Dictionary
Origin: Fr atavisme < L atavus, father of a great-grandfather, ancestor < at-, beyond + avus, grandfather < IE *ati, beyond + *awos, maternal grandfather
See atavism in American Heritage Dictionary 4
Origin: French atavisme
Origin: , from Latin atavus, ancestor
Origin: : atta, father
Origin: + avus, grandfather; see awo- in Indo-European roots.
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