"The conservative has little to fear from the man whose reason is the servant of his passions, but let him beware of him in whom reason has become the greatest and most terrible of passions. These are the wreckers of outworn empires."

“If human evolution is to continue along the same lines as in the past, it will probably involve a still greater prolongation of childhood and retardation of maturity. Some of the characters distinguishing adult man will be lost. It was not an embryologist or palaeontologist who said, "Except ye . . . become as little children, ye shall not enter into the kingdom of heaven.”

“There is no great invention, from fire to flying, which has not been hailed as an insult to some god.”

“The universe is not only queerer than we imagine, but queerer than we can imagine.”

“If the only available genes produce rather large changes, disadvantageous one at a time, then it seems to me probable that evolution will not occur in a random mating population. In a self-fertilised or highly inbred species it may do so if several mutations useful in conjunction, but separately harmful, occur simultaneously. Such an event is rare, but must happen reasonably often in wheat...”

“It seems to me immensely unlikely that mind is a mere by-product of matter. For if my mental processes are determined wholly by the motions of atoms in my brain I have no reason to suppose that my beliefs are true. They may be sound chemically, but that does not make them sound logically. And hence I have no reason for supposing my brain to be composed of atoms.”

“At Oxford, the young Haldane was frequently asked whether he was related to the "famous John Scott Haldane", his father, and he would answer "That depends on whether you consider identity to be a relationship.”