34 
get the actual mean, or a series of individuals 
symmetrically arranged around that mean. 
This would involve more or less atavism, be- 
cause the potentialties of the germs are derived 
from past generations, and include many repe- 
titions, more or less complete, of phases which 
have lately, owing to the incidence of selection, 
been permitted no development. But I cannot 
see, with Mr. Reid, that there would be un- 
limited atavism, because when the atavistic 
changes had proceeded from B to A, the B- 
features would become ancestral, and a new 
atavism, from A to B, would appear. Thus at 
some point there would be reached a condition 
of equilibrium, and the tendency to vary in any 
particular direction would be lost. Existing 
species may be compared to elastic bodies under 
stress, the stress being natural selection. When 
the stress ceases, there is contraction until the 
condition of equilibrium is reached, but cer- 
tainly not indefinite contraction. 
The second portion of the book consists of a 
discussion of human evolution against zymotic 
diseases and narcotics. Mr. Reid argues that 
the way to tell in what direction the evolution 
of a species is tending is to observe the causes 
of mortality. Applying this test to man, he 
concludes that as disease is the principal cause 
of death it must be against disease that we are 
evolving. He then proceeds to show that those 
races which have long been subjected to a par- 
ticular disease, e. g., malaria or consumption, 
have acquired a relative immunity from it, or 
at least a power of enduring its attacks. The 
whole matter is set forth very clearly and is 
well worth reading. While it cannot be denied 
that the factor of zymotic disease is an extremely 
important one, hitherto generally overlooked 
in discussions on human evolution, I must say 
that I think Mr. Reid himself has overlooked 
some not less important factors. The ‘social 
efficiency ’ of a people, as Mr. B. Kidd rightly in- 
sisted, isa factor of immense importance. Thus, 
in this very matter of zymotic diseases, how 
greatly is the death rate in an epidemic (and 
the existence of the epidemic itself) influenced 
by the social condition of the people, and even 
by their intellectual and moral condition, as re- 
flected in the municipal government and sani- 
tary arrangements! Thus, while, as Mr. Reid 
SCIENCE. 
[N. 8S. Vou. VI. No. 181. 
shows, the negro is under identical conditions 
far less affected by malaria than white people, 
Dr. J. 8. Billings has to report, in summing up 
the statistics for 28 cities of the United States, 
that the deaths from malarial fever were more 
than three times as numerons, in proportion to 
the population, among the colored people as 
among the whites. It is fair to state that 
under the term ‘colored’ the includes the 
Chinese, etc., but the difference is conspicuous 
in those cities which are known to contain a 
large negro population. Mr. Reid may reply 
that sanitary arrangements and forms of goy- 
ernment, affecting all, select nobody; but cer- 
tainly they do select the citizens of one town, 
State or country as against others, or those of 
the rural districts as against the towns. Thus 
the population of large cities, like London, is 
perpetually replenished from the rural districts. 
A pure-bred cockney of the fourth generation 
is said by J. M. Fothergill to be very rare. 
Further, as Dr. Billings has shown (11th Census 
of the United States) the death-rate in every 
large city varies enormously in the different 
wards, and this must be due mainly to the mode 
of life of the people, their food, sanitation, and 
other matters directly connected with social 
efficiency. Still again, there is a tremendous 
proportion of infant mortality, a large part of 
which must be due to unfavorable conditions 
of the mother or child. Thus it must neces- 
sarily be that, while there are inequalities in 
morality and intelligence, the most moral and 
the most intelligent races or groups of people 
will be favorably selected in the struggle for 
existence. 
The whole subject is one of immense com- 
plexity, and in studying the statistics one has 
to be constantly on the lookout for sources of 
error, which are numerous and confusing. But 
there is no doubt that Mr. Reid’s discussion is a. 
valuable one, if only it draws attention to mat- 
ters which have been too much overlooked. 
The final portion of the book, treating of 
evolution, against alcohol and other narcotics, 
seems to me to contain a fundamental error. 
It is assumed that a desire for alcohol is inherent 
in the human race, and that, since the substance 
cannot be banished, our only salvation is to 
gradually acquire a toleration of it, as of a 
