RACE ASSIMILATION BY THE. 
PURE-SIRE METHOD 
Harry H. LAuGHLtn, Sc.D. 
Assistant Director, Eugenics Record Office 
HILE it has been demonstrated 
\ \ to the satisfaction of students of 
pedigrees that in most species 
the ancestral contributions of the dam 
and the sire are about equal, still on 
account of physiological and_ social 
considerations the pure-sire method 
is much more potent than a possible 
pure-dam method would be in race 
improvement. The principal reason is 
that physiologically the reproductive 
capacities of the race are limited, not 
by the number of fertile sires, but by 
the number of fertile dams. But in the 
human race almost equally potent is 
this social or mate-selection factor 
whereby the women of the lower races 
usually show a preference for men of 
higher racial levels. Furthermore the 
mores of most states cast less social 
obloquy upon the fathers than upon 
the mothers of an illegitimate child, and 
similarly less reproach is directed 
toward a legitimate mating between a 
man belonging to a “‘high’”’ race and a 
woman of “‘inferior’’ blood than toward 
the reverse type of marriage. 
RACE-MIXTURE IN EARLY 
AMERICA 
SPANISH- 
In historic times we have interesting 
examples of race improvement or 
assimilation by a process which is 
quite analogous to the pure-sire method 
with which we are familiar in the 
animal kingdom. In the early days 
of Spanish America, there were many 
more men than women who came from 
the mother country and settled in the 
new world. The result was that there 
began almost immediately a process 
of race-mixture which was quite lacking 
in the regions settled by the northern 
European colonists. In the latter case 
the immigration to the new world con- 
sisted largely of colonists and their 
families who came into a comparatively 
unsettled country in search of new 
1J. Deniker, The Races of Man, 1913, p. 542. 
homes, whereas in the case of Spain, 
the conquistadors—armies of men alone 
—came seeking wealth, adventure and 
colonial possessions. 
From the social side, we find in the 
new world this situation: the average 
Spaniard, or man with considerable 
Spanish blood, would of necessity, on 
account of the scarcity of Spanish 
women, have to remain a bachelor or 
marry a wife with less Spanish blood 
on the average, than he himself carried. 
The result was, from the standpoint of 
the Spaniard, that his offspring were of 
less pure Spanish descent, while from 
the standpoint of the native Indian or 
imported negro, the offspring were of a 
decidedly higher racial level. 
EFFICACY OF THE PURE-SIRE METHOD 
It appears that a man with “‘a touch”’ 
of Indian or negro blood could return 
to Spain with his Spanish father and 
enter Spanish society much more 
readily than could a daughter with 
Indian or colored blood. The process 
of race assimilation by the pure-sire 
method became so common in Latin 
America that there developed a definite 
system of nomenclature! for describing 
the products of each particular genera- 
tion of offspring. The accompanying 
pedigree-chart shows this process in 
detail, and attention is called to the 
sureness with which race assimilation 
is achieved by clinging to the pure-sire 
method, whereas in case this system is 
dropped, confusion results and a mixed 
race is the product. 
The efficacy of the pure-sire method 
is doubly assured when we remember 
that in man, as in other animals, the 
germ-plasm is not indefinitely dilut- 
able, but segregates into chromosomes 
which in their entirety (barring cross- 
ing-over) either do or do not pass from 
a given ancestor to the offspring. 
We shall not go into this matter here, 
