1 92 1. J Suhspecies and Evolution. 535 



I would here draw attention to a valuable paper on 

 " Inheritance o£ Acquired Characters " by Professor 

 MacBride in the January number o£ ' Science Progress.' 

 From exjieriments 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 

 bo 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 wdiich is appreciable to the human eye. But if that 

 same European settles in the tropics, the cumulative efloct 

 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. 



SER. XI. VOL. III. 2 N 



