Haldane and the Emergence of Modern Evolutionary Theory 69This means that the number of recessive alleles (a) will increase if 1 +un <
K
k, that is, ∆x>0.
(^31) Therefore, recessive alleles for altruistic behavior can
increase in proportion only if they are already common. However, sinceunwill
also increase, this process will end. Similar results are obtained if the altruism
trait is dominant. Haldane concluded that “the biological advantages of altruistic
conduct only outweigh the disadvantages if a substantial proportion of the tribe
behave altruistically. If only a small fraction behaves in this manner, it has a very
small effect on the viability of the tribe, not sufficient to counterbalance the bad
effect on the individuals concerned” (p. 209).
Moreover, for altruism to spread, the proportion of altruists need not be great
ifKk is large. In fact, for a recessive altruism trait, ifKk >
√
N, a single altruistic
individual is sufficient. Thus, for small groups there always is effective selection
for altruism. However, in large groups, according to Haldane, “the initial stages
of the evolution of altruism depend not on selection, but on random survival” (p.
209). This had some bearing on possible human altruism:
If any genes are common in mankind which promote conduct biologi-
cally disadvantageous to the individual in all types of society, but yet
advantageous to society, they must have spread when man was divided
into small endogamous groups. As many eugenists have pointed out,
selection in large societies operates in the reverse direction.... I find it
difficult to suppose that many genes for absolute altruism are common
in man (pp. 209–210).
5 THE AFTERMATH
There is one relatively uncontroversial sense in which the joint work of Fisher,
Haldane, and Wright was both similar and important: it provides a quantitative
account of the effects of selection acting on Mendelian populations. With the
publication ofCausesin 1932, one chapter in the history of evolutionary theory
— and the only chapter to which Haldane made decisive contributions — came to
a close. Whereas Fisher and Wright continued to refine their respective theories of
evolution until their deaths, Haldane largely turned aside from evolutionary theory
in the 1930’s and his subsequent contributions to that theory were sporadic.
What is lost in this broad picture is the extent to whichCausesdiffered from
Fisher’s and Wright’s work. Fisher [1930] argued that evolution proceeded by con-
tinuous selection acting upon single genes, each being only subjected to a small
selective pressure, in large populations. He showed that the frequencies of each
gene would reach an equilibrium but, and this ultimately was the source of pro-
gressive change in Fisher’s theory, the environment deteriorated. So selection had
to continue, as the species struggled to keep up with the environment.
(^31) Haldane [1932, 209] reports the relation as 1 +un>K
k which is incorrect. However, his
discussion (pp. 209–210) is based on the correct result!