A discussion between Haldane and a friend began to take a predictable turn. The friend said with a sigh, 'It's no use going on. I know what you will say next, and I know what you will do next.' The distinguished scientist promptly sat down on the floor, turned two back somersaults, and returned to his seat. 'There,' he said with a smile. 'That's to prove that you're not always right.'

An attempt to study the evolution of living organisms without reference to cytology would be as futile as an account of stellar evolution which ignored spectroscopy.

Capitalism, though it may not always give the scientific worker a living wage, will always protect him, as being one of the geese which produce golden eggs for its table.

Coming to the question of life being found on other planets, Professor Haldane apologized for discoursing, as a mere biologist, on a subject on which we had been expecting a lecture by a physicist [J. D. Bernal]. He mentioned three hypotheses:
(a) That life had a supernatural origin,
(b) That it originated from inorganic materials, and (c) That life is a constituent of the Universe and can only arise from pre-existing life. The first hypothesis, he said, should be taken seriously, and he would proceed to do so. From the fact that there are 400,000 species of beetle on this planet, but only 8,000 species of mammals, he concluded that the Creator, if he exists, has a special preference for beetles, and so we might be more likely to meet them than any other type of animal on a planet which would support life.

Haldane was engaged in discussion with an eminent theologian. 'What inference,' asked the latter, 'might one draw about the nature of God from a study of his works?' Haldane replied: 'An inordinate fondness for beetles.'

I am quite sure that our views on evolution would be very different had biologists studied genetics and natural selection before and not after most of them were convinced that evolution had occurred.

I have tried to show why I believe that the biologist is the most romantic figure on earth at the present day. At first sight he seems to be just a poor little scrubby underpaid man, groping blindly amid the mazes of the ultra-microscopic, engaging in bitter and lifelong quarrels over the nephridia of flatworms, waking perhaps one morning to find that someone whose name he has never heard has demolished by a few crucial experiments the work which he had hoped would render him immortal.

I'd lay down my life for two brothers or eight cousins.

If materialism is true, it seems to me that we cannot know that it is true. If my opinions are the result of the chemical processes going on in my brain, they are determined by the laws of chemistry, not those of logic.

It was a reaction from the old idea of “protoplasm”, a name which was a mere repository of ignorance.

Man armed with science is like a baby with a box of matches.

My final word, before I'm done,
Is 'Cancer can be rather fun'—
Provided one confronts the tumour
with a sufficient sense of humour.
I know that cancer often kills,
But so do cars and sleeping pills;
And it can hurt till one sweats,
So can bad teeth and unpaid debts.
A spot of laughter, I am sure,
Often accelerates one's cure;
So let us patients do our bit
To help the surgeons make us fit.

My practice as a scientist is atheistic. That is to say, when I set up an experiment I assume that no god, angel or devil is going to interfere with its course; and this assumption has been justified by such success as I have achieved in my professional career. I should therefore be intellectually dishonest if I were not also atheistic in the affairs of the world.

Now my own suspicion is that the Universe is not only queerer than we suppose, but queerer than we can suppose.

Quantitative work shows clearly that natural selection is a reality, and that, among other things, it selects Mendelian genes, which are known to be distributed at random through wild populations, and to follow the laws of chance in their distribution to offspring. In other words, they are an agency producing variation of the kind which Darwin postulated as the raw material on which selection acts.

Science affects the average man and woman in two ways already. He or she benefits by its application driving a motor-car or omnibus instead of a horse-drawn vehicle, being treated for disease by a doctor or surgeon rather than a witch, and being killed with an automatic pistol or shell in place of a dagger or a battle-axe.

The advance of scientific knowledge does not seem to make either our universe or our inner life in it any less mysterious.

The conclusion forced upon me in the course of a life devoted to natural science is that the universe as it is assumed to be in physical science is only an idealized world, while the real universe is the spiritual universe in which spiritual values count for everything.

[John Scott Haldane] preferred to work on himself or other human beings who were sufficiently interested in the work to ignore pain or fear .... [His] object was not to achieve this state of [pain or fear] but to achieve knowledge which could save other men's lives. His attitute was much more like a good soldier who will risk his life and endure wounds in order to gain victory than that of an ascetic who deliberately undergoes pain. The soldier does not get himself wounded deliberately, and my father did not seek pain in his work though he greeted pain which would have made some people writhe or groan, with laughter.

[T]he idea of protoplasm, which was really a name for our ignorance, [is] only a little less misleading than the expression “Vital force”.

The foundations of population genetics were laid chiefly by mathematical deduction from basic premises contained in the works of Mendel and Morgan and their followers. Haldane, Wright, and Fisher are the pioneers of population genetics whose main research equipment was paper and ink rather than microscopes, experimental fields, Drosophila bottles, or mouse cages. Theirs is theoretical biology at its best, and it has provided a guiding light for rigorous quantitative experimentation and observation.

Genetics is the first biological science which got in the position in which physics has been in for many years. One can justifiably speak about such a thing as theoretical mathematical genetics, and experimental genetics, just as in physics. There are some mathematical geniuses who work out what to an ordinary person seems a fantastic kind of theory. This fantastic kind of theory nevertheless leads to experimentally verifiable prediction, which an experimental physicist then has to test the validity of. Since the times of Wright, Haldane, and Fisher, evolutionary genetics has been in a similar position.