Letter | Published:

An Unnoticed Factor in Evolution

Nature volume 31, page 194 | Download Citation



I AM surprised that the letter of Mr. Catchpool in NATURE (vol. xxxi. p. 4) has remained unnoticed by your correspondents. His hypothesis that mutual sterility may be the cause, not the result, of specific divergence, is, I think, quite in accordance with many observed facts. The buffalo and the ox, the sheep and the goat, have lived for ages side by side without, as far as I am aware, a hybrid between either of them having been produced. Mule or hinny hybrids between the horse and the ass are obtained easily, but the offspring is rarely fertile, so rare, that the British Consul at Granada told me, when I was there, that he had never known of a case, although in Spain mules exist in thousands. Amongst bovine animals many species produce hybrids which are apparently perfectly fertile; those between the Indian ox and the gayal, species of different genera, Bos and Bibos, are common, and their fertility is shown by the existence of numerous intermediate hybrids. There is living at the Zoological Gardens at the present time, a hybrid between the Indian ox, the gayal, and the bison, and, by her side, a hybrid between herself and a bison. The offspring of the cross between many species of ducks are perfectly fertile. This I have repeatedly seen in the case of the hybrids between the tufted duck and the pochard. I think there is another unnoticed factor in evolution. The scent of animals plays an important part in their sexual relationships, and “sports” in this respect are as likely to occur as in the organs of the body; thus the peculiar odours of the sheep and the goat may be mutually repulsive.

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  1. Chirbury, Beckenham, Kent, December 15, 1884



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