535 
1921 .] Subspecies and Evolution. 
I would here draw attention to a. valuable paper on 
“ Inheritance o£ Acquired Characters ” by Professor 
MacBride in the January number of 4 Science Progress.’ 
From experiments conducted by Kammerer on Salamanders 
and Midwife-Toads, it would appear that acquired characters 
are indeed heritable. 
To sum up, I believe that nearly all evolution is the 
cumulative effect of environment, which acts with greater 
force and rapidity on isolated communities than on widely- 
distributed continental communities. 
Weissmann, in his work on the Germ-Plasm, has been 
severely criticised for inferring that environment can 
directly influence the germ-cells without affecting the body- 
tissue in which the germ-cell is contained. This I believe to 
be partly correct, and I consider environment can affect the 
gamete to the following extent. If a European pays a 
visit to a tropical climate, his skin becomes tanned and 
brown under the influence of the sun’s rays. The colour of 
his skin is naturally not transmitted to his offspring to any 
degree which is appreciable to the human eye. But if that 
same European settles in the tropics, the cumulative effect 
of the sun’s rays on countless generations will permanently 
affect the colour of the skin by a very gradual process, and 
an eventual dark-skinned race will become established. I 
do not doubt that the germ-cell changes in exact proportion 
to the degree of permanence which cumulative environ¬ 
mental effect has on the body-tissue. 
3 . Are geographical races incipient species ? 
Where no isolation exists, geographical races will almost 
invariably be connected by intermediate forms in inter¬ 
mediate areas, and such intermediate areas may be but 
a mile or so in extent, or they may extend to a hun¬ 
dred miles or so ; but such geographical races, when 
so constructed, can, in our opinion, never become species. 
It therefore follows that only isolated geographical races 
are incipient species, but to this end isolation must be 
complete. 
SEE. XI.—VOL. III. 2 N 
