THE PRESENT EVOLUTION OF MAN — PHYSICAL 241 



when attacking races that they have little or not at all 

 afflicted. Judging by current literature, this difference 

 of type is generally regarded as something altogether 

 inexplicable, or sometimes it has been said that 

 this or that race has become acclimatized to this or 

 that disease, when the common and very foolish error 

 has been made of imagining that a phenomenon named 

 is a phenomenon explained. To say that a race has 

 become acclimatized to a disease — i.e. that it has become 

 more resistant to it — does not explain how that increase 

 of resisting power arose. When in rare cases an 

 attempt has been made to probe deeper, it has gener- 

 ally been on lines of the Lamarkian doctrine of the 

 transmissibility of acquired traits ^ ; and as often as not 

 it has been made by thinkers who possibly never heard 

 of Lamark, and who would repudiate the logical outcome 

 of their own arguments — the idea of evolution. Start- 

 ing with the fact, that in many zymotic diseases one 

 attack confers immunity against subsequent attacks, it 

 has been tacitly assumed, if not expressly asserted, that 

 this acquired immunity, or some of it, is transmitted 

 from parent to child, each successive individual of the 

 line beginning life with more resisting power than his 

 parent began with, and transmitting more to his off- 

 spring than he received. But besides the general con- 

 siderations which lead us to denj' the transmissibility of 



^ " The opinion has been expressed that syphilis becomes milder 

 in communities in which it has long been present. It is reputed 

 to have become in Portugal a much enfeebled malady from this 

 cause. An English physician practising there has expressed his 

 belief that, owing to the habitual neglect of efficient treatment, 

 the whole community has become influenced. We know that 

 this law of transmitted partial immunity prevails in the other 

 specific fevers. If small-pox be introduced to a new soil, it is 

 far more severe and fatal than when it occurs in a community 

 which through many generations has been accustomed to its 

 prevalence ; so also with measles and scarlet fever." — J. Hutchin- 

 son, Syphilis, pp. 389-90. 



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