十九世纪初，英国出生了一位自然科学巨人，名叫查尔斯·达尔文（1809年-1882年），德国也出生了一位思想巨人，名叫卡尔·马克思（1818年-1883年）。他们几乎属于同龄人，两者都堪称十九世纪最具革命性的思想家。
马克思以政治难民流亡在英国，创作他的传世名著《资本论》时，其实距离达尔文不到20英里远的地方，而达尔文在同时创作了宏大的生物史观《物种起源》。
是恩格斯将《物种起源》介绍给马克思的，马克思读后立即写信给恩格斯：“尽管该书写得有点儿英国式的粗糙，但它包含了支持我们的观点的自然历史基础。”（Although it is developed in the crude English style, this is a book which contains the basis of natural history for our views. Karl Marx on Darwin's On the Origin of Species December, 1860）
1873年，马克思把新近出版的《资本论》第一卷第二版寄给了达尔文一本，并在扉页上题签：“查尔斯·达尔文先生：您的诚实的仰慕者，卡尔·马克思，伦敦，1873年6月16日”。（Mr Charles Darwin on the part of his sincere admirer Karl Marx.）
马克思送给达尔文的这本《资本论》，他从来没有读过，至今还在达尔文故居纪念馆（Down House)，大部分书页还没有开封。（He never read Marx's book, the vast majority of whose pages remained uncut in his library.）
1873年10月1日，达尔文给马克思回了一封信，信中写到：“阁下馈赠《资本论》大作，令我不胜荣幸之至；并真诚希望敝人能对政治经济学有更深的理解，以不负您的馈赠。尽管我们所研究的领域如此不同，敝人相信我等皆渴望知识的延展，并确信长此以往必定会为人类福祉有所贡献。”
原文：
Dear Sir:
I thank you for the honour which you have done me by sending me your great work on Capital; & I heartily wish that I was more worthy to receive it, by understanding more of the deep and important subject of political Economy. Though our studies have been so different, I believe that we both earnestly desire the extension of Knowledge, & that this is in the long run sure to add to the happiness of Mankind.
I remain, Dear Sir
Yours faithfully,
Charles Darwin
Letter from Charles Darwin to Karl Marx
October, 1873
有学者提到，六年后，马克思写信给达尔文，请求赠送给他第二卷，但是达尔文拒绝了，他解释道：“如果他和这么一本无神论的书发生联系，将给他的某些家庭成员带来痛苦。”（Six years later, Marx wrote to Darwin, requesting permission to dedicate his next volume to him. But Darwin declined the offer, explaining that "it would pain certain members of his family if he were associated with so atheistic a book.")
http://www.creationmoments.com/radio/transcripts/charles-darwin-and-karl-marx
这个说法来源于1931年苏联报刊刊登的一封1880年10月13日“达尔文写给马克思”的信，这封信混在马克思的手稿里：http://friendsofdarwin.com/articles/marx/
原文：
Dear Sir:
I am much obliged for your kind letter & the Enclosure.— The publication in any form of your remarks on my writing really requires no consent on my part, & it would be ridiculous in me to give consent to what requires none. I shd prefer the Part or Volume not to be dedicated to me (though I thank you for the intended honour) as this implies to a certain extent my approval of the general publication, about which I know nothing.— Moreover though I am a strong advocate for free thought on all subjects, yet it appears to me (whether rightly or wrongly) that direct arguments against christianity and theism produce hardly any effect on the public; & freedom of thought is best promoted by the gradual illumination of men's minds, which follow from the advance of science. It has, therefore, always been my object to avoid writing on religion, & I have confined myself to science. I may, however, have been unduly biased by the pain which it would give some members of my family , if I aided in any way direct attacks on religion.— I am sorry to refuse you any request, but I am old & have very little strength, and looking over proof-sheets (as I know by present experience) fatigues me much.
I remain Dear Sir,
Yours faithfully,
Ch. Darwin
从这封信来看，达尔文的确拒绝了一本赠书，但拒绝的是不是马克思的《资本论》的第二卷呢？这个谜底最终由加州大学（University of California）学者Margaret Fay 根据一本1881年出版的书“The Students' Darwin”揭开。
“The Students' Darwin”一书的作者Edward Aveling是马克思的女儿Eleanor的情人。1895年，他和Eleanor一起整理从恩格斯那里继承的马克思手稿。1897年，Aveling写了一篇文章“马克思和达尔文”，文章提到他曾经和达尔文有过通信。有一个可能性是，他把达尔文写给他的信和马克思的手稿混在一起了。
最终，一封签署日期为1880年10月12日由Edward Aveling写给达尔文的信在剑桥大学的达尔文手稿中被发现，信的内容是尚未出版的“The Students' Darwin”一书的样章，信中请求赠送一本书给达尔文。但是达尔文以上述理由拒绝了。
所以不是马克思的《资本论》的第二卷被达尔文所拒绝，而是Edward Aveling的“The Students' Darwin”一书。
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