e
with its ever branching and beautiful ramifications.

5. LAWS OF VARIATION.

Effects of external conditions. Use and disuse, combined with natural
selection; organs of flight and of vision. Acclimatisation. Correlation
of growth. Compensation and economy of growth. False correlations.
Multiple, rudimentary, and lowly organised structures variable. Parts
developed in an unusual manner are highly variable: specific characters
more variable than generic: secondary sexual characters variable.
Species of the same genus vary in an analogous manner. Reversions to
long lost characters. Summary.

I have hitherto sometimes spoken as if the variations--so common and
multiform in organic beings under domestication, and in a lesser degree
in those in a state of nature--had been due to chance. This, of course,
is a wholly incorrect expression, but it serves to acknowledge plainly
our ignorance of the cause of each particular variation. Some authors
believe it to be as much the function of the reproductive system to
produce individual differences, or very slight deviations of structure,
as to make the child like its parents. But the much greater variability,
as well as the greater frequency of monstrosities, under domestication
or cultivation, than under nature, leads me to believe that deviations
of structure are in some way due to the nature of the conditions of
life, to which the parents and their more remote ancestors have been
exposed during several generations. I have remarked in the first
chapter--but a long catalogue of facts which cannot be here given would
be necessary to show the truth of the remark--that the reproductive
system is eminently susceptible to changes in the conditions of life;
and to this system being functionally disturbed in the parents, I
chiefly attribute the varying or plastic condition of the offspring. The
male and female sexual elements seem to be affected before that union
takes place which is to form a new being. In the case of "sporting"
plants, the bud, which in its earliest condition does not apparently
differ essentially from an ovule, is alone affected. But why, because
the reproductive system is disturbed, this or that part should vary more
or less, we are profoundly ignorant. Nevertheless, we can here and there
dimly catch a faint ray of light, and we may feel sure that there must
be some cause for each deviation of structure, however slight.

How much direct effect difference of c