52 NATURAL SCIENCE [JuLy 
is examined, and the conclusion is reached that it is not sufficient to 
make any great difference—half the adolescent members of the 
second generation being produced by less than 29 per cent. of the 
first. 
It is evident that any character, possessed by this original 29 
per cent. of ‘“superfertile ” couples, will quickly spread among suc- 
cessive generations, unless it be extremely disadvantageous to its 
possessors ; and as an example of the complicated problem presented 
by this result, it may be mentioned that Professor Pearson found, 
on examining 206 families, that the mean height of 133 men, 
fathers of less than five children each, was half an inch greater than 
the mean height of 73 men, each of whom was father of more than 
five children; but these 73 men produced between them 561 chil- 
dren, the 133 less fertile producing only 394 children. On the 
other hand, the more fertile mothers were sensibly taller than the 
less fertile. Perhaps no example could show more clearly than this 
the complex nature of the phenomena with which the student of 
animal evolution has to deal, and the absurdity of tryimg to deal 
with them otherwise than by the patient numerical evaluation of each 
factor separately. 
The last essay to which attention can here be called is that on 
“Variation in Man and Woman.’ The object is to support the con- 
tention that women are on the whole more variable than men; and 
an immense series of measurements has been collected, in many of 
which—such, for example, as the cephalic index, the stature at par- 
ticular ages, and others—this is undoubtedly the case. But it must 
be borne in mind that Professor Pearson refuses to consider “ second- 
ary sexual characters,” and that he proposes a peculiar measure of 
variability. What exactly the rejection of secondary sexual char- 
acters means, it is difficult to understand; surely any character, 
other than the structure of the reproductive organs, may be called a 
secondary sexual character, if the two sexes differ with respect to 
it; and if this definition be adopted, Professor Pearson’s position 
becomes unintelligible; if, on the other hand, the term be limited 
to those characters which are directly affected by sexual selection, 
then Professor Pearson should not permit himself to discuss the 
relative variability of a particular organ in men and in women with- 
out first showing that marriages occur at random so far as that 
organ is concerned. No definition of a secondary sexual character 
is offered in the essay, which is apparently directed against some 
rash persons who have asserted that every character is more variable 
in men than in women, and who attempt to deduce social and 
practical consequences from this proposition. 
A more important point is the assumption “that the only useful 
sense in which we can study relative variability is by endeavouring 
