Formerly Milton's Paradise Lost had been my chief favourite, and in my excursions during the voyage of the Beagle, when I could take only a single small volume, I always chose Milton.

Nothing is easier than to admit in words the truth of the universal struggle for life, or more difficult - at least I have found it so - than constantly to bear this conclusion in mind...We behold the face of nature bright with gladness...We do not see, or we forget, that the birds which are idly singing round us mostly live on insects and seeds, and are thus constantly destroying life.

But then 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?

If every one were cast in the same mould, there would be no such thing as beauty.

But when on shore, & wandering in the sublime forests, surrounded by views more gorgeous than even Claude ever imagined, I enjoy a delight which none but those who have experienced it can understand.

[Herschel and Humboldt] stirred up in me a burning zeal to add even the most humble contribution to the noble structure of Natural Science. No one or a dozen other books influenced me nearly so much as these two. I copied out from Humboldt long passages about Teneriffe and read them aloud on one of [my walking excursions].

Even the humblest mammal's strong sexual, parental, and social instincts give rise to 'do unto others as yourself' and 'love thy neighbor as thyself'.