ABSTRACTS
La Nature de l'Atavisme. J. LEÔP. FRATEUR. (Emeritus Professor,
University of Louvain) (1939). Annales de Medecine Veterinaire 11, 461-476.
A TAVISM is the reappearance of an ancestral character when that character, though
present, is not manifested directly by the parents (i.e. is latent). This latency
can be (a) geno typic, i.e. resulting from the inactivity of actual hereditary characters, or
(b) phenotypic, i.e. due to the absence of environmental conditions suitable to the mani-
festation of that particular character. Real hereditary characters, as distinguished
from acquired characters, are permanent and, though they can be modified by environ-
ment, they will continue to be transmitted from generation to generation through the
process of reproduction.
Hereditary character is nearly always composed of a certain number of components
of which it is the result. These components are as old as the species to which the indivi-
dual manifesting them belongs and cannot be spontaneously generated. The gametes
alone are capable of transmitting hereditary characters and. the substratum of these,
which represents the hereditary character, is an integral part of the germ cells of new
individuals. Hereditary characters are transmitted (a) jointly by the ovum and sper-
matazoon (homozygous characters, duplex or pure) or (b) through only one of these re-
productive organisms (heterozygous characters, simple or impure). A character mani-
festing itself as a result of the foreign element in the reproductive cells is not hereditary
and will persist no longer than the foreign element which causes it (e.g. the transmission
of a contagious or parasitic disease.)
There are two types of acquired characters which are frequently confused (a) pheno-
typic modifications and (b) acquired characters proper. Phenotypic modifications are
variations of characters dependent upon environment. Acquired characters proper,
however, appear anew in any given generation and disappear at the end of it without
leaving a trace. They are acquired from without, hereditary characters come from
within. There is, however, in creatures which evince these acquired characters, a heredi-
tary aptitude which permits of their acquisition (e.g. man is hereditarily articulate but
the ability to talk in any particular language is acquired)
All hereditary characters are the result of a well defined invariable chain of biochemi-
cal reactions, the final results of which vary only according to the environment in which
they take place. Each hereditary character is independent of other hereditary characters
and has its own structure which is nearly always complex, composed of a number of
primary components. Once dissociated, they are capable of recombining themselves in
all conceivable variat ons, thus producing a series of new, secondary characters, but
whatever may be the combination in which the components are engaged, they never
lose their individuality. When two heterozygous individuals unite a certain percentage
of their descendants present a common character.
Genotypical short termed atavism is the phenomenon of the reappearance in a des-
cendant or a recessive character which manifested itself previously in some ancestor,
without being apparent in the immediate parents. A character is recessive when it com-
prises fewer of the primary components than another character of the same species. A
dominant character is one which completely conceals other characters which are present.
It should be noted that some characters assume complete dominance (qualitative) and
others only a partial dominance (quantitative). A dominant qualitative character (simple
or double) can entirely obscure a recessive character with which it is associated. A
quantitative character on the other hand, only dominates the character on which it super-
imposes itself, if it is double or homozygous. In the single state, the other character is
partially manifested (e.g. the white quantitative character of an Andulasian fowl super-
imposed on a black colour is white when it is homozygous or double, and grey when it is
heterozygous or simple.)
Genotypical long term atavism is the phenomenon caused by the combination of pri-
mary characters into the ancient hereditary character (e.g. the reappearance of characters
existing in the species). Primitive character (always complex and formed of a large
number of primary components) disappears following dissociation of the components
( 324 )