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, etc., 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
recur.]

In some cases, as with the pig, rabbit, etc., and with those plants which are
valued for their seed, the direct selection of the more fertile individuals
has probably much increased their fertility; and in all cases this may have
occurred indirectly, from the better chance of some of the numerous offspring
from the more fertile individuals having been preserved. But with cats,
ferrets, and dogs, and with plants like carrots, cabbages, and asparagus,
which are not valued for their prolificacy, selection can have played only a
subordinate part; and their increased fertility must be attributed to the more
favourable conditions of life under which they have long existed.


CHAPTER 2.XVII.

ON THE GOOD EFFECTS OF CROSSING, AND ON THE EVIL EFFECTS OF CLOSE
INTERBREEDING.

DEFINITION OF CLOSE INTERBREEDING.
AUGMENTATION OF MORBID TENDENCIES.
GENERAL EVIDENCE OF THE GOOD EFFECTS DERIVED FROM CROSSING, AND ON THE EVIL
EFFECTS FROM CLOSE INTERBREEDING.
CATTLE, CLOSELY INTERBRED; HALF-WILD CATTLE LONG KEPT IN THE SAME PARKS.
SHEEP.
FALLOW-DEER.