Ivi MEMOIR. 
scattered through the herbarium in their natural orders, which is scarcely 
according to a native’s notions. That of the cow-tree he remembers as a 
species of sapotaciz, without flowers or fruit, and therefore indetermin- 
able. In answer to your long and full-of-interest letter, 1 have rather an 
absurd request to make—that you would return me my last if you have not 
destroyed it. I have almost forgotten its tenor; and Mr. Darwin, who 
is extremely interested in yours, has asked me and you to let him 
see mine to you, when, if you care for it, it shall be returned to you 
forthwith. 
‘‘True, as you say, it #zay be that ‘ characters acquired through the action 
of local conditions’ are propagated. I grant that my antagonistic position 
to this view is not based on any good foundation; to tell you the truth it 
rests, as a Jr7nciple, very much on an inherent prejudice in my mind against 
attributing one natural phenomenon to the operation of two distinct laws or 
operations of nature. If variation will do it all, and you allow variation to 
accumulate ad lzbztum, why call up any other frz7e cause ? and complicate 
unnecessarily what otherwise is a very simple rationaie, however inexplicable, 
until, at any rate, some clear case of such propagation of z7dwzced character is 
brought forward. I am quite aware that this is a very unsatisfactory answer, 
and you know that I do not hold the original proposition as an irrefragable 
truth, and only say I am prone to believe that way. There is a great deal in 
what you say as to use and disuse, and this I grant is a very formidable 
argument against the position I adopt. It does apparently stand to reason 
that organs present, but not used, should atrophy; but this does not demand 
the propagation of the atrophied state acquired by the individual. A.g., 
say that organ ‘little finger’ falls out of use—it is no longer then a 
matter of indifference to you whether it is present or no; if present and 
not in use it #wst be in the way, therefore be prejudicial. Therefore, 
amongst the variously developed fingers of the progeny, those individuals 
will be preserved which have smallest little fingers, and so on ad 
extinction. The male nipple shows how little mere disuse has to do with 
the abolition of an organ, so long as it is not in the way. Your case of 
the races of man inhabiting tropics of America and Africa is a most 
remarkable and interesting one. Again, your observation that ‘ local 
physical conditions do not directly produce a race,’ is a pregnant one— 
‘a dozen different varieties in a single spot’ is a wonderful fact, and gives 
a deep insight into the laboratory of Nature. Your expression of natural 
selection ‘drawing out’ the varieties, is a happy one. 1 do not remember 
Darwin using it. 
‘‘ Have you read Asa Gray’s review, etc., of Darwin? If not I can lend 
you them. He had one exquisite illustration of little streams guided by the 
finger to form a great river. I forget it exactly. 
‘The moral barrier checking frequent intermarriages no doubt plays a 
great part; in other words, ‘ physiological obstacles’ are great. These first, 
perhaps, lead to forms taking separate geographical areas, and hence being 
brought into contact with other forms, just as children of a family centrifugate 
from the parental house, and as a rule do not marry their cousins and blood 
relations—not out of any social or moral obstacle, but in obedience to the 
centrifugal tendency. 
