poultry, or duck, or rabbit fancier, who was not fully convinced that each
main breed was descended from a distinct species. Van Mons, in his treatise
on pears and apples, shows how utterly he disbelieves that the several
sorts, for instance a Ribston-pippin or Codlin-apple, could ever have
proceeded from the seeds of the same tree. Innumerable other examples could
be given. The explanation, I think, is simple: from long-continued study
they arc strongly impressed with the differences between the several races;
and though they well know that each race varies slightly, for they win
their prizes by selecting such slight differences, yet they ignore all
general arguments, and refuse to sum up in their minds slight differences
accumulated during many successive generations. May not those naturalists
who, knowing far less of the laws of inheritance than does the breeder, and
knowing no more than he does of the intermediate links in the long lines of
descent, yet admit that many of our domestic races have descended from the
same parents--may they not learn a lesson of caution, when they deride the
idea of species in a state of nature being lineal descendants of other
species?"


The actual causes of variation are unknown. Mr. Darwin favors the opinion
of the late Mr. Knight, the great philosopher of horticulture, that
variability tinder domestication is somehow connected with excess of food.
He regards the unknown cause as acting chiefly upon the reproductive system
of the parents, which system, judging from the effect of confinement or
cultivation upon its functions, he concludes to be more susceptible than
any other to the action of changed conditions of life. The tendency to vary
certainly appears to be much stronger under domestication than in free
Nature. But we are not sure that the greater variableness of cultivated
races is not mainly owing to the far greater opportunities for
manifestation and accumulation--a view seemingly all the more favorable to