The general fact of a segregated people (or individuals of an animal species) becoming best adapted to the particular climate, etc., through Natural Selection is clear enough, the best adapted alone surviving in the long run, and the peculiarities transmitted by the close breeding. But what your statements tend to make out is, not the tendency of a human race to return to its original type, but only the tendency of the causes which produced a certain effect once, to produce it again, the circumstances continuing,--to produce it in the Fellahs as it produced it in the remote ancestors of the Pharaohs. That is all safe enough. But your case does not prove that unless you make out that the Egyptian race was nearly destroyed by crossings. I do not know, but I doubt if you can show that the crossings were ever enough to modify the Egyptian people, at least the common people, who make up the bulk. Slight infusions, you see, would be worked out. The foreign though conquering race would be less prolific and less enduring than the native, etc., etc. So is it not likely that in the Fellahs you have the representatives of the old Egyptians continued, not reproduced, as your remarks would partly lead one to suppose your meaning? Besides, once having got a race you must not make too much of climate, to the overlooking of the wonderful persistence of any variety when close bred. See the Jews: the nose remains hooked, etc., under all climates. Again, in your last sentence. When you _unscientific 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 particular 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 people 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 adaptations 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.