reversion vs atavism

reversion and atavism both are nouns.

Word	Noun	Adjective	Verb	Adverb
reversion	Yes	No	No	No
atavism	Yes	No	No	No

As nouns, reversion and atavism are synonyms defined as:

Other synonyms of reversion include throwback.

reversion (noun)	atavism (noun)
a failure to maintain a higher state	a reappearance of an earlier characteristic
turning in the opposite direction
returning to a former state
(genetics) a return to a normal phenotype (usually resulting from a second mutation)
a reappearance of an earlier characteristic
(law) an interest in an estate that reverts to the grantor (or his heirs) at the end of some period (e.g., the death of the grantee)