Take a species with a million pairs of individuals--half of
these vary sufficiently, either + or -, in the four acquired characters
A, B, C, D: what will be the proportion of individuals that vary + in
these four characters according to the law of averages? Will it not be
about 1 in 64? If so it is ample--in many cases--for Natural Selection
to work on, because in many cases less than 1/64 of offspring survives.
On Romanes' view of the impossibility of Natural Selection doing
anything alone, because the required coincident variations do not occur,
the occurrence of a "strong man" or a racehorse that beats all others
easily must be impossible, since in each of these cases there must be
scores of coincident favourable variations.
Given sufficient variation, I believe divergent modification of a
species in two lines could easily occur, even if free intercrossing
occurred, because, the numbers varying being a large proportion of the
whole, the numbers which bred like with like would he sufficient to
carry on the two lines of divergence, those that intercrossed and
produced less perfectly adapted offspring being eliminated. Of course
some amount of segregate breeding does always occur, as Darwin always
maintained, but, as he also maintained, it is not absolutely essential
to evolution. Romanes argues as if "free intercrossing" meant that none
would pair like with like! I hope you will have another slap at him, and
withdraw or explain that unlucky "infinity to one," which is Romanes'
sheet-anchor.
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