Heredity and sex / by Thomas Hunt Morgan.

  • Thomas Hunt Morgan
Date:
1913
Catalogue details

Licence: Attribution-NonCommercial 4.0 International (CC BY-NC 4.0)

Credit: Heredity and sex / by Thomas Hunt Morgan. Source: Wellcome Collection.

    29/306 (page 13)
    THE EVOLUTION OF SEX 13 túnate to measure the importance of every result by its relation to the theory of evolution. But with this understanding I may venture upon a few suggestions. If a variation should arise in a hermaphroditic species (already reproducing sexually) that made cross- fertilization more likely than self-fertilization, and if, as a rule, the hybrid condition (however this may be explained) is more vigorous in the sense that it leaves more offspring, such a variation would survive, other things being equal. But the establishment of the contrivance in the species by means of which it is more likely to cross- fertilize, might in another sense act as a drawback. Should weak individuals appear, they, too, may be perpetuated, for on crossing, their weakness is concealed and their offspring are vigorous owing to their hybrid condition. The race will be the loser in so far as re¬ cessive or weak combinations will continue to appear, as they do in many small communities that have some deficiency in their race ; but it is a question whether the vigor that comes from mixing may not more than com¬ pensate for the loss due to the continual appearance of weakened individuals. This argument applies to a supposed advantage within the species. But recombination of what already exists will not lead to the development of anything that is essentially new. Evolution, however, is con¬ cerned with the appearance and maintenance of new characters. Admitting that sexual reproduction proved an advantage to species, and especially so when com¬ bined with a better chance of cross-fertilization, the machinery would be at hand by means of which any