HUMAN FECUNDITY 95 



natural conditions ; in captivity they experience two annual 

 heats like the dog.^ The otter in the wild state breeds but once 

 a year ; in captivity oestrous may occur at regular monthly 

 intervals all the year round.^ Bears are monoestrous in the w^ild 

 state ; in the Zoological Gardens oestrous may be experienced 

 for two or three months.^ With regard to the Ungulata we have 

 numerous facts of the same nature. The red deer offers the best 

 example ; under natural conditions there are two dioestrous 

 cycles lasting three weeks ; in captivity the sexual season extends 

 over the whole year.* The facts are somewhat similar in respect 

 to cattle and horses. Examples might also be taken from other 

 mammalian classes. The wild rabbit breeds from February to 

 May ; in captivity the sexual season lasts nearly the whole year. 

 Further it may be noticed that among lower groups good 

 conditions are, as is well known, markedly favourable to increased 

 fecundity. 



Before we go on to look into the causes of this increase in 

 fecundity, it may be noticed that the number of young produced 

 at a birth among domestic species is on an average greater than 

 that produced by the wild ancestor. This evidence, it will be 

 observed, refers to the third factor which bears upon the increase 

 in fecundity. The wild rabbit is said to produce at the most six 

 young at a time ; the tame rabbit has four to eleven, and a case 

 is known in which eighteen were born, all of which survived.^ The 

 wild sow bears from four to eight, and sometimes twelve, young. 

 The domestic sow is considered to be of no value unless she 

 produces at least eight at a birth. Equally remarkable examples 

 are to be found outside the Mammals. ' The hen of Gallus bankiva 

 lays from six to ten eggs ; the tame one in the course of a year 

 from eighty to one hundred.' 



7. It is clear that one common feature in the conditions sur- 

 rounding domesticated species and civilized man, as compared 

 with species in a state of nature, is the increase in the richness and 

 regularity of the food-supply, and the general betterment of the 

 environment. In fact, just as this increase in the richness of the 

 surroundings may increase the length of the mature period, so 

 it may increase the number at a birth and also decrease the 



1 Marshall, loc. cit., p. 57. - Ibid., p. 59. ^ Heape, loc. cit., p. 15. 



* Ibid., p. 15. * This and the following examples are taken from Darwin, 



Variations of Animals and Plan's und&r Domestication, vol. ii, p. 90. 



