atavism vs reversion

atavism and reversion both are nouns.

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

As nouns, atavism and reversion are synonyms defined as:

Other synonyms of atavism include throwback.

atavism (noun)	reversion (noun)
a reappearance of an earlier characteristic	a failure to maintain a higher state
	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)