Letter from Charles Darwin to Asa Gray, 1856, discussing his 
developing ideas concerning the origin and mutation of species. 
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Down Bromley Kent July 20 (1856) 
My dear Dr. Gray: 
What you say about extinction, in regard to such genre and 
local disjunction, being hypothetical seems very just. Some- 
thing direct however, can be advanced on this head from fossil 
shells; but hypothetical such notions must remain. It is not 
a little egotistical, but I should like to tell you, (and I do 
not think I have) how I view my work. Nineteen years (I) ago 
it occurred to me that whilst attention employed on Natural 
History I jnight perhaps do good if I noted any sort of facts 
bearing on the question on the origin of species; and this I 
have since been doing. Either species have been independently 
created, or they have descended from other species, like vari- 
eties from one species. I think it can be shown to be probable 
that man gets his most distinct varieties by preserving such as 
arise best worth keeping and destroying the others, but I should 
fill a quire if I were to go on. To be brief I as sume that 
species arise like our domestic varieties with much extinction; 
and then test this hypothesis by comparison with as many general 
and pretty well established propositions as I can find made out, 
in geographic distribution, geological history, affinities etc. 
etc. etc. And it seems to me, that suuposing that such hypothesis 
were to explain such general propositions, we ought in accordance 
with common way of following all sciences, to admit it, till 
some better hypothesis be found out. For to my mind to say the 
species were created so and so is no scientific explanation but 
a prescient ( if ic) way of saying it is so and so. But it is not 
sensible trying to show how I try to proceed in compass of a note. 
But as an honest man I must tell you that I have come to the 
relentless conclusion that there are no such things as independent- 
ly created species, the species are only strongly defined varieties. 
I know that this will make you despise me. I do not much under- 
rate the many huge difficulties on this view, but yet it seems 
to me to explain too much, otherwise inexplicable, to be false. 
Just to allude to one point in your last note, viz about species 
of the same genus generally having a common or continuous area: 
if they are actual lineal descendents of one species, this of 
course would be the case; and the sadly too many exceptions (for 
me) have to be explained by climactic and geological changes. A 
fortiori on this view (but on exactly same grounds) all the indi- 
viduals of the same species should have a continuous distribution. 
On this latter kind of subject I have put a chapter together .and 
Hooker kindly read it over: I thought the exception(s) and diffi- 
culties were so great that on the whole the balance weighed against 
my notions, but I was much pleased to find that it seemed to have 
considerable weight with Hooker, who said he had never been so 
