66 THE PHYSIOLOGY OF REPRODUCTION 



spending to conceptions in May and June. . . . ( )bservations tend to 

 show the largest number of conceptions in Sweden falling in June ; 

 in Holland and France, in May-June ; in Spain, Austria, and Italy, 

 in May ; in Greece, in April. That is, the farther south, the earlier 

 the spring and the earlier the conceptions." Other facts of a like 

 kind are recorded by Westermarck, who concludes that primitive 

 man had an innate tendency towards increased powers of reproduc- 

 tion at the end of spring or beginning of summer, and that this 

 tendency became variously modified under the influence of natural 

 selection in the different human races which subsequently arose. 1 



Finally, it may be pointed out that Westerinarck's conclusion 

 which seems a very probable one in view of the evidence which he 

 and others have collected is in no way invalidated by the fact that 

 the human female experiences normally an uninterrupted succession 

 of dia'strous (i.<: menstrual) cycles ; for, as already shown, a similar 

 condition is known to exist in several at least of the lower Primates, 

 with which there is also evidence that in a state of nature the 

 breeding functions are restricted to particular seasons of the year.- 



Win-tin i- thi- iiHiim-xfrtinx <>r f/ic /W//'/.s//v)/>\ rnnditinn is the more 

 primitive is a question which cannot at present be decided The 

 fact that polyopstrum is secondarily acquired among many animals 

 may perhaps be regarded as evidence that monoestrum is the more 

 primitive of the two conditions ; for, as already shown, there are 

 numerous instances of Mammals which are almost certainly 

 mono3strous in their wild state, but which have independently 

 assumed a condition of polycestrum under the more luxurious 

 influences of domestication. Thus, while the sheep, the sow, and 

 the cat are almost certainly monu'strous in a state of nature, the 

 domesticated breeds of these animals show a varying degree of 



1 Mayo-Smith (/or. cit.) points out that .sexual pel -iodicity in civilised man is 

 much obscured by social influences. "One great social influence is the time 

 of marriage. Marriage tends to accumulate about the social festivities of 

 Christmas time, and in Catholic countries especially in the period just before 

 Lent." He suggests that in agricultural districts the concentration about 

 Christmas is due to the leisure following the labours of the autumn. "In 

 cities the births are more evenly distributed, showing that artificial life has 

 overcome the influence of seasons and particular occupations." 



- That is to say that, whereas menstruation goes on at regular intervals all 

 the year round, the proiestrous or menstrual periods are only followed during 

 the breeding season by <estri at which it is possible for conception to occur. 

 There are some indications that the sexual instinct among males is also 

 periodic, both in the lower Primates and in the human subject, but the 

 periodicity is not so marked as among females. Havelock Kllis (/<,r. n't., has 

 discussed this question at some length, adducing evidence of a sexual rhythm 

 in men. See especially appendix to Ellis's \\-ork by Perry-Coste, who shows 

 that there may be a tendency towards rhythmic regularity in the sexual 

 functions as manifested especially in the recurrence of seminal emissions. 



