Genetic Progress by Voluntarily Conducted Germinal Choice 
additional defectives (or an equivalent excess of others) fail to 
have offspring. However, it would be wishful thinking to suppose 
this to be the case. There is no evidence of an over-all posi- 
tive correlation today between effective reproductive rate and 
soundness of body, mind, or temperament, aside from cases of 
extreme defect too rare to influence the trend to an important 
extent. 
On the contrary, negative partial correlations have repeatedly 
been found between reproductive rate, on the one hand, and the 
rank of the parents in such social classifications as economic 
status or education, on the other hand. This has been the case 
not only in the Western world but even in the U.S.S.R. Now 
educational and economic status, although certainly not genetic 
categories, do have important genetic contingents, especially 
in societies not having very rigorous class divisions. Moreover, 
it is hardly credible that the factors that give rise to the observed 
negative correlations would be able to distinguish between the 
differences that depend on environmental influences and those 
that depend on genes, so as to allow the environmental differ- 
ences but not the genetic ones to be responsible for all of the 
negative correlations found. We therefore return to the con- 
clusion that genetically based ability and reproductive rate are 
today negatively correlated. 
Attacking the matter from another angle, a consideration of 
the attitudes and practices of people in general, in technologi- 
cally advanced societies, provides telling clues concerning the 
most prevalent causes of present-day differences in family size. 
It is obvious that in the main these differences no longer depend, 
as they did in the past, on how many children the person or 
couple are able to have, but rather on, first, the extent to which 
they aim to limit conception and, second, the extent to which 
they succeed in attaining this aim. It is not the having of child- 
ren but the prevention of them which today requires the more 
active, responsible effort, an effort which makes demands on 
the participants’ prudence, initiative, skill, and conscience. 
It seems evident that persons possessed of greater foresight, 
and those with keener regard for their family, usually aim to 
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