Innocent light-minded men, who think that astronomy can be learnt by looking at the stars without knowledge of mathematics, will become birds; those who have no philosophy will become wild land-animals; the very stupidest will become fishes.
 Bertrand Russell, A History of Western Philosophy (1945). copy citation

Context

“There is some curious physiology, as, that the purpose of the intestines is to prevent gluttony by keeping the food in, and then there is another account of transmigration. Cowardly or unrighteous men will, in the next life, be women. Innocent light-minded men, who think that astronomy can be learnt by looking at the stars without knowledge of mathematics, will become birds; those who have no philosophy will become wild land-animals; the very stupidest will become fishes. The last paragraph of the dialogue sums it up: We may now say that our discourse about the nature of the universe has an end. The world has received animals, mortal and immortal, and is fulfilled with them, and has become a visible animal containing the visible—the sensible God who is the image of the intellectual, the greatest, best, fairest, most perfect—the one only-begotten heaven.” source