ly
prolific in Lapland. Hard living, also, retards the period at which animals
conceive; for it has been found disadvantageous in the northern islands of
Scotland to allow cows to bear calves before they are four years old.[243]

Birds offer still better evidence of increased fertility from
domestication: the hen of the wild _Gallus bankiva_ lays from six to
ten eggs, a number which would be thought nothing of with the domestic
hen. The wild duck lays from five to ten eggs; the tame one in the
course of the year from eighty to one hundred. The wild grey-lag goose
lays from five to eight eggs; the tame from thirteen to eighteen, and
she lays a second time; as Mr. Dixon has remarked, "high-feeding, care,
and moderate warmth induce a habit of prolificacy which becomes in some
measure hereditary." Whether the semi-domesticated dovecot pigeon is
more fertile than the wild rock-pigeon _C. livia_, I know not; but the
more thoroughly domesticated breeds are nearly twice as fertile as
dovecots: the latter, however, when caged and highly fed, become
equally fertile with house pigeons. The peahen alone of domesticated
birds is rather more fertile, according to some accounts, when wild in
its native Indian home, than when domesticated in Europe and exposed to
our much colder climate.[244]

With respect to plants, no one would expect wheat to tiller more, and
each ear to produce more grain, in poor than in rich soil; or to get in
poor soil a heavy crop of peas or beans. Seeds vary so much in number
{113} that it is difficult to estimate them; but on comparing beds of
carrots saved for seed in a nursery garden with wild plants, the former
seemed to produce about twice as much seed. Cultivated cabbages yielded
thrice as many pods by measure as wild cabbages from the rocks of South
Wales. The excess of berries produced by the cultivated Asparagus in
comparison with the wild plant is enormous. No doubt many highly
cultivated plants, such as pears, pineapples, bananas, sugar-cane, &c.,
are nearly or quite sterile; and I am inclined to attribute this
sterility to excess of food and to other unnatural conditions; but to
this subject I shall presently recur.

In some cases, as with the pig, rabbit, &c., and with those plants which
are valued for their seed, the direct selection of the more fertile
individuals has probably muc