Man scans with scrupulous care the character and pedigree of his horses, cattle, and dogs before he matches them; but when he comes to his own marriage he rarely, or never, takes any such care.

Intelligence is based on how efficient a species became at doing the things they need to survive.

[Alexander von Humboldt was the] greatest scientific traveller who ever lived.

It is not the most intellectual of the species that survives; it is not the strongest that survives; but the species that survives is the one that is able best to adapt and adjust to the changing environment in which it finds itself.

As man advances in civilization, and small tribes are united into larger communities, the simplest reason would tell each individual that he ought to extend his social instincts and sympathies to all members of the same nation, though personally unknown to him. This point being once reached, there is only an artificial barrier to prevent his sympathies extending to the men of all nations and races.

It at once struck me that under these circumstances favourable variations would tend to be preserved, and unfavourable ones to be destroyed.

It is absurd to talk of one animal being higher than another...we consider those, where the intellectual faculties most developed as the highest. - A bee doubtless would [use] ... instincts as a criteria.