Man still bears in his bodily frame the
indelible stamp of his lowly origin
Charles Darwin quotation

We must, however, acknowledge, as it seems to me, that man with all his noble qualities, with sympathy which feels for the most debased, with benevolence which extends not only to other men but to the humblest living creature, with his god-like intellect which has penetrated into the movements and constitution of the solar system — with all these exalted powers — Man still bears in his bodily frame the indelible stamp of his lowly origin.
This quote comes from Charles Darwin's later work - The Descent of Man (1871) Ch. XXI : General Summary And Conclusion

Shortly after returning from his voyaging on HMS Beagle, in 1836, Charles Darwin began to keep a number of "Notebooks" to record his thoughts on various topics. Another " indelible stamp of his lowly origin " type quote is to be found in his Notebook "M" dating from these early times in Darwin's intellectual history:-

"Our descent, then, is the origin of our evil passions!! The devil under form of Baboon is our grandfather."

Charles Darwin's On the Origin of Species was first published in 1859. He had actually privately outlined this theory in the early 1840s but had delayed publication due to considerations of his wishing to gather more proof and of not wishing to offend social and religious sensibilities.

In a letter to W. Graham of July 3, 1881, Charles Darwin wrote:-

"With me, the horrid doubt always arises whether the convictions of man's mind, which has been developed from the mind of the lower animals, are of any value or at all trustworthy. Would any one trust in the convictions of a monkey's mind, if there are any convictions in such a mind?"

There are many entertaining and instructive quotations about, or attributable to, Charles Darwin:-

For instance as a boy of sixteen his father said to him:-

"You care for nothing but shooting, dogs and rat-catching, and you will be a disgrace to yourself and all your family."

Darwin was keenly interested in Natural History as a young man and his Autobiography mentions one particular beetle hunt in detail:-

  "I will give a proof of my zeal: one day on tearing off some old bark, I saw two rare beetles and seized one in each hand; then I saw a third and new kind, which I could not bear to lose, so that I popped the one which I held in my right hand into my mouth. Alas it ejected some intensely acrid fluid, which burnt my tongue so that I was forced to spit the beetle out, which was lost, as well as the third one".

Our own favourite Darwin quote is, however, a very significant one which is to be found in a confidential letter of 11 January 1844 to a fellow scientist named Joseph Hooker.
In this letter Darwin, speaking about how he had spent his time after his voyaging on HMS Beagle, wrote that:-

"I have been now ever since my return engaged in a very presumptuous work & which I know no one individual who w^d not say a very foolish one.— I was so struck with distribution of Galapagos organisms &c &c & with the character of the American fossil mammifers, &c &c that I determined to collect blindly every sort of fact, which c^d bear any way on what are species.— I have read heaps of agricultural & horticultural books, & have never ceased collecting facts— At last gleams of light have come, & I am almost convinced (quite contrary to opinion I started with) that species are not (it is like confessing a murder) immutable. Heaven forfend me from Lamarck nonsense of a “tendency to progression” “adaptations from the slow willing of animals” &c,—but the conclusions I am led to are not widely different from his—though the means of change are wholly so— I think I have found out (here's presumption!) the simple way by which species become exquisitely adapted to various ends.— You will now groan, & think to yourself ‘on what a man have I been wasting my time in writing to.’— I sh^d, five years ago, have thought so.— "