Far from depending upon any general physiological law, the rut is thus adapted to the requirements of each species separately. Here again we have an example of the powerful effects of natural selection, often showing themselves very obviously. The dormouse (_Muscardinus avellanarius_), for instance, that feeds upon hazel-nuts, pairs in July, and brings forth its young in August, when nuts begin to ripen. Then the young grow very quickly, so that they are able to bear the autumn and winter cold.[129]
There are, however, a few wild species, as some whales,[130] the elephant,[131] many Rodents,[132] and several of the lower monkeys,[133] that seem to have no definite pairing season. As to them it is, perhaps, sufficient to quote Dr. Brehm’s statement with reference to the elephant, “The richness of their woods is so great, that they really never suffer want.”[134] But the man-like apes do not belong to this class. According to Mr. Winwood Reade, the male Gorillas fight at the rutting season for their females;[135] Dr. Mohnike, as also other authorities, mentions the occurrence of a rut-time with the Orang-utan.[136] And we find that both of these species breed early in the season when fruits begin to be plentiful,—that is, their pairing time depends on the same law as that which prevails in the rest of the animal kingdom.
Sir Richard Burton says, “The Gorilla breeds about December, a cool and dry month; according to my bushmen, the period of gestation is between five and six months.”[137] I have referred this important statement to Mr. Alfred R. Wallace, who writes as follows: “From the maps of rain distribution in Africa in Stanford’s ‘Compendium,’ the driest months in the Gorilla country seem to be January and February, and these would probably be the months of greatest fruit supply.” As regards the Orang-utan, Mr. Wallace adds, “I found the young sucking Orang-utan in May; that was about the second or third month of the dry season, in which fruits began to be plentiful.”
Considering, then, that the periodicity of the sexual life rests on the kind of food on which the species lives, together with other circumstances connected with anatomical and physiological peculiarities, and considering, further, the close biological resemblance between man and the man-like apes, we are almost compelled to assume that the pairing time of our earliest human or half-human ancestors was restricted to a certain season of the year, as was also the case with their nearest relations among the lower animals. This presumption derives further probability from there being, even now, some rude peoples who are actually stated to have an annual pairing time, and other peoples whose sexual instinct undergoes most decidedly a periodical increase at a certain time of the year.