HERMANN J. MULLER 
A similar situation exists, but the selective pressure is weaker, 
in cases of genes that lead the individual to help not just his 
immediate family but also others of a small, genetically closely 
related group to which he belongs. For in directing his help 
preferentially to them he is, again reflexively, tending to help 
the multiplication of whatever distinctive genes had been 
operative in this behaviour, since these genes are likely to exist 
in greater concentration among his relatives than among other 
individuals taken at random. Obviously, however, the larger 
the community to which he extends such help, the lower is the 
relevant resemblance between his genetic constitution and theirs, 
and the weaker, for that reason, is the resulting reflexive selec- 
tion. Moreover, when groups are larger they are fewer, and 
then offer correspondingly less choice for any process of selec- 
tion which, like that under consideration here, operates among 
them as wholes. Thus, selection for altruistic propensities has 
tended to work chiefly for those traits that cause help to be 
given very near to home?. 
An additional factor lies in the survival value of such feelings 
of reciprocity as are represented by the expression “‘I help him 
who helps me”’. For these feelings may arise between unrelated 
individuals and even in such a case they are by their nature 
reflexive. That is, they tend to redound to the benefit of the 
first participant, and so to the multiplication of the very genes 
that underlie the given social feelings. It should be noted, how- 
ever, that this process does not include selection for the impulse 
to turn the other cheek or to love one’s enemy: quite the con- 
trary, for a form of reciprocative disposition would tend to be 
selected which, though returning help for help, also gave blow 
for blow, or took an eye for an eye, since that behaviour also is 
reflexive, by affording defence to one’s own genes. 
However, cultural progress inevitably led men into ever larger 
associations, which tended to engulf or squeeze out the smaller 
groups. Thus even strangers had to learn to behave amicably 
towards one another, and according to generally accepted rules 
of conduct. Under these circumstances the principle of recipro- 
cation, applied to strangers, both privately and publicly, must 
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