242 THE PRESENT EVOLUTION OF MAN — PHYSICAL 



acquired traits in multicellular organisms, and therefore 

 of the transmissibility of the effects of disease, there 

 are certain facts, drawn from the study of disease itself, 

 which sufficiently negative the opinion that traits 

 acquired under such influence are transmissible. No 

 immunity can be acquired against tuberculosis and 

 malaria, the two most death-dealing of all diseases ; or 

 at least no immunity can be acquired against tubercu- 

 losis, and if any is acquired against malaria it is quickly 

 lapsed, as in relapsing fever, in the intervals between the 

 paroxysms. Experience by the individual of either of 

 these diseases weakens rather than strengthens him 

 against them. If the above, the Lamarkian theory, be 

 correct, it follows, therefore, that races which have had 

 a long and disastrous experience of tuberculosis and 

 malaria should be less resistant than races that have had 

 little or no experience of them. Each successive indi- 

 vidual of the line should begin life with less resisting 

 power than his parent began with, and should transmit 

 less than he received to his offspring. The contrary, 

 however, is the case, for races that have had a long and 

 disastrous experience of tuberculosis and malaria are 

 more resistant than races that have had little or no ex- 

 perience of them ; thus the Englishman who migrates to 

 the West Coast of Africa falls an easier victim to malaria 

 than does the negro, whereas the negro who migrates to 

 England falls an easier victim to tuberculosis than does 

 the Englishman. In both cases, not only is the disease 

 more readily acquired by the stranger, but, when ac- 

 quired, it is much more deadly to him than to the man 

 whose race has had an extended experience of it. In 

 both cases, though experience of the disease by the 

 individual rather weakens than strengthens his power 

 of resistance to it, yet prolonged experience of the 

 disease by the race does not result in a weakening of 

 its resisting power, but in a conspicuous strengthening 



