462 LETTERS TO DARWIN AND OTHERS. [1863, 



Again, in your last sentence. When you unscien- 

 tific people take up a scientific principle you are apt to 

 make too much of it, to push it to conclusions beyond 

 what is warranted by the facts. But, because a par- 

 ticular race has persisted in Egypt, how do you know 

 that it is the only race capable of perpetuating itself ? 



If there had been a large infusion of different peo- 

 ple in Egypt, and if they had exterminated the old 

 race, do you not suppose this would have established 

 itself, perpetuated itself, and that its particular adap- 

 tations to the climate would have been different from 

 that of the present race? 



If you cut off all future immigration into North 

 America, would the Indians resume possession of the 

 country ? or else our descendants become a copper- 

 colored race ? 



Enough for the present. When you have cracked 

 these nuts, send me, if you please, another sheet. 



Ever yours cordially, ASA GRAY. 



CAMBRIDGE, July 6, 1863. 



DEAR BRACE, Yours of 20th ult. came just as J. 

 was off for New Haven and I getting ready to go to 

 her aid. 



We came back only on Thursday, or rather Friday 

 morning. My hands so full that I could not write to 

 Darwin, to whom I owe a long letter, till to-night. I 

 will now inclose your note. 



It would be very like a chemist to think that exter- 

 nal influences will explain everything. But I pre- 

 sume he believes that peculiarities are heritable. If 

 he does, then he thinks he can explain, or will be able 

 to explain, the origination of variations. I cannot, 

 that is, to any extent, and do not expect to. When 



