INBREEDING AND OUTBREEDING 
Review of the Evidence by East and Jones Shows that the Influence of these 
Factors Depends Wholly on the Inherited Traits Present 
Paut PoPpENOE 
XW phases of genetics have in the 
Fk past been surrounded with more 
superstition and ignorance than 
inbreeding, and few phases have 
been more thoroughly cleared up by 
experimental breeding during recent 
years. A comprehensive book on the 
subject is therefore timely, and Dr. 
East and Dr. Jones are well qualified 
to assemble and weigh the evidence on 
the subject, for they themselves have 
provided some of the best of it.2 
The importance of an understanding 
of inbreeding and outbreeding is by no 
means limited to the plant-breeders and 
animal husbandmen. The authors 
suggest three questions which will show 
what important sociological bearings 
exist : 
1. Do marriages between near rela- 
tives, wholly by reason of their consan- 
guinity, regardless of the inheritance 
received, affect the offspring adversely ? 
2. Are consanguineous marriages 
harmful through the operation of the 
laws of heredity? 
3. Are hereditary differences in the 
human race transmitted in such a man- 
ner as to make matings between mark- 
edly different peoples desirable or un- 
desirable, either from the standpoint 
of the civic worth of the individual, or 
of the stamina of the population as a 
whole? 
After discussing briefly the question 
of reproduction and the mechanism of 
heredity, the authors turn to a consid- 
eration of the experiments on which 
modern ideas of inbreeding and out- 
breeding are based. These experiments 
are well known to readers of the 
JourNAL oF Hereprry and need not be 
rehearsed. Some of them have lasted 
for nearly fifteen years of the closest 
possible inbreeding, the most valuable 
data being derived from maize, rats and 
guinea-pigs. 
IS INBREEDING INJURIOUS ? 
lew students will differ from the 
authors when they conclude that “in- 
breeding has but one demonstrable 
effect on organisms subjected to its 
action—the isolation of homozygous 
types. The diversity of the resulting 
types depends directly upon the number 
of heterozygous hereditary factors pres- 
ent in the individuals with which the 
process is begun; it is likely, therefore, 
to vary directly with the amount of 
cross-breeding experienced by their 
immediate ancestors. The rapidity of 
the isolation of homozygous types is a 
function of the intensity of the inbreed- 
ing.” 
“Are, then, the immediate results of 
inbreeding sometimes injurious? In 
naturally cross-fertilized organisms they 
most emphatically are—nay, more, even 
disastrous—when we recall the reduc- 
tion to over one-half or one-third in 
production in grain and a corresponding 
decrease in size of plant and rate of 
growth in maize. But maize is prob- 
ably an extreme case. With other 
organisms the results are not so bad, 
and in some cases, especially when 
selection has been made, no evil effects 
1Tnbreeding and Outbreeding: Their genetic and sociological significance,” by Edward 
M. Fast, Ph.D., Harvard University, Bussey Institution, and Donald F. Jones, D.Sc. 
Connecticut Agricultural Experimental Station. Pp. 285, with 46 illus. Monographs on Ex- 
perimental Biology, J. B. Lippincott Co., Philadelphia and London, 1919. Price, $2.50 net. 
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