[At high school in Cape Town] my interests outside my academic work were debating, tennis, and to a lesser extent, acting. I became intensely interested in astronomy and devoured the popular works of astronomers such as Sir Arthur Eddington and Sir James Jeans, from which I learnt that a knowledge of mathematics and physics was essential to the pursuit of astronomy. This increased my fondness for those subjects.

[N]o scientist likes to be criticized. … But you don’t reply to critics: “Wait a minute, wait a minute; this is a really good idea. I’m very fond of it. It’s done you no harm. Please don’t attack it.” That's not the way it goes. The hard but just rule is that if the ideas don't work, you must throw them away. Don't waste any neurons on what doesn’t work. Devote those neurons to new ideas that better explain the data. Valid criticism is doing you a favor.

All that biology tells us about the nature of God is that he has “An inordinate fondness for beetles.”

For myself, I found that I was fitted for nothing so well as for the study of Truth; as having a mind nimble and versatile enough to catch the resemblances of things (which is the chief point) , and at the same time steady enough to fix and distinguish their subtler differences; as being gifted by nature with desire to seek, patience to doubt, fondness to meditate, slowness to assert, readiness to reconsider, carefulness to dispose and set in order; and as being a man that neither affects what is new nor admires what is old, and that hates every kind of imposture. So I thought my nature had a kind of familiarity and relationship with Truth.

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.”

Man … begins life as an ambiguous speck of matter which can in no way be distinguished from the original form of the lowest animal or plant. He next becomes a cell; his life is precisely that of the animalcule. Cells cluster round this primordial cell, and the man is so far advanced that he might be mistaken for an undeveloped oyster; he grows still more, and it is clear that he might even be a fish; he then passes into a stage which is common to all quadrupeds, and next assumes a form which can only belong to quadrupeds of the higher type. At last the hour of birth approaches; coiled within the dark womb he sits, the image of an ape; a caricature of the man that is to be. He is born, and for some time he walks only on all fours; he utters only inarticulate sounds; and even in his boyhood his fondness for climbing trees would seem to be a relic of the old arboreal life.

One of the petty ideas of philosophers is to elaborate a classification, a hierarchy of sciences. They all try it, and they are generally so fond of their favorite scheme that they are prone to attach an absurd importance to it. We must not let ourselves be misled by this. Classifications are always artificial; none more than this, however. There is nothing of value to get out of a classification of science; it dissembles more beauty and order than it can possibly reveal.