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'.

Every new body of discovery is mathematical in form, because there is no other guidance we can have.

It is interesting to contemplate an entangled bank clothed with many plants of many kinds with birds singing on the bushes, with various insects flitting about and with worms crawling through the damp earth and to reflect that these elaborately constructed forms so different from each other and dependent on each other and so complex a manner have all been produced by laws acting around us.

It is not the strongest of the species that survives, nor the most intelligent that survives. It is the one that is the most adaptable to change, that lives within the means available and works co-operatively against common threats.

Linnaeus and Cuvier have been my two gods, though in very different ways, but they were mere schoolboys to old Aristotle.

But Geology carries the day: it is like the pleasure of gambling, speculating, on first arriving, what the rocks may be; I often mentally cry out 3 to 1 Tertiary against primitive; but the latter have hitherto won all the bets.

On seeing the marsupials in Australia for the first time and comparing them to placental mammals: “An unbeliever . . . might exclaim 'Surely two distinct Creators must have been at work'”