Amazing how quickly the past becomes idyllic. - Margaret Atwood

Nobody is any authority on the fucks other people give,

“All it takes,” said Crake, “is the elimination of one generation. One generation of anything. Beetles, trees, microbes, scientists, speakers of French, whatever. Break the link in time between one generation and the next, and it’s game over forever.”

These things sneak up on him for no reason, these flashes of irrational happiness. It's probably a vitamin deficiency.