from The American Heritage® Dictionary of the English Language, 4th Edition
- n. The reappearance of a characteristic in an organism after several generations of absence, usually caused by the chance recombination of genes.
- n. An individual or a part that exhibits atavism. Also called throwback.
- n. The return of a trait or recurrence of previous behavior after a period of absence.
from Wiktionary, Creative Commons Attribution/Share-Alike License
- n. The reappearance of an ancestral characteristic in an organism after several generations of absence.
- n. The recurrence or reversion to a past behaviour, method, characteristic or style after a long period of absence.
- n. Reversion to past primitive behavior, especially violence.
from the GNU version of the Collaborative International Dictionary of English
- n. The recurrence, or a tendency to a recurrence, of the original type of a species in the progeny of its varieties; resemblance to remote rather than to near ancestors; reversion to the original form.
- n. The recurrence of any peculiarity or disease of an ancestor in a subsequent generation, after an intermission for a generation or two.
- n. recurrence of or reversion to a past style, outlook, approach, or manner.
from The Century Dictionary and Cyclopedia
- n. In biology, reversion, through the influence of heredity, to ancestral characters; resemblance exhibited by a given organism to some remote ancestor; the return to an early or original type by its modified descendants; restoration of structural characters which have been lost or obscured.
- n. In pathology, the recurrence of any peculiarity or disease of an ancestor in remote generations.
from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.
- n. a reappearance of an earlier characteristic
The term atavism is employed to express the reappearance of characters, physical or psychical, in the individual, or in the race, which are supposed to have been possessed at one time by remote ancestors.
No clear conception as to its true nature had been formulated, and even the propriety of designating the observed phenomena by the term atavism seemed doubtful.
The origin (perhaps rather the distinction) of species is accounted for principally by the last named law, by means of which Eimer also explains the so-called atavism or reversion.
Lombroso, and the Italian school of criminologists generally, attribute crime chiefly to atavism, that is, reversion to primitive types.
It is generally called atavism, or better, systematic atavism, and the clearest cases are those in which a quality which is latent in the greater part of a family or group, becomes manifest in one of its members.
First of all the question arises as to whether the case is one of real atavism, or is only seemingly so, being due to hybrid or otherwise impure descent of the varying individual, and secondly whether it may be only an instance of the regularly  occurring so-called atavism of the sporting varieties with which we shall deal in a later lecture.
The examples given may suffice to convey a general idea of the phenomenon, ordinarily called atavism by gardeners, and considered mostly to be the effect of some innate tendency to revert to the ancestral form.
Many instances of so-called atavism are of purely morphologic nature.
Used in this way, this term has the same bearing as the word atavism of the breeders, but it has the advantage of indicating the true cause thereof.
But this process, which is transforming us from savages into civilized men, is a very slow one; and now and then there occur cases of what physiologists call atavism, or reversion to an ancestral type of character.