All that can really be said is that at some indeterminate point in the very distant past, for reasons… — Bill Bryson

In France, a chemist named Pilatre de Rozier tested the flammability of hydrogen by gulping a mouthful and blowing across an open flame, proving at a stroke that hydrogen is indeed explosively combustible and that eyebrows are not necessarily a permanent feature of one's face.

It is natural human impulse to think of evolution as a long chain of improvements, of a never-ending advance towards largeness and complexity — in a word, towards us. We flatter ourselves. Most of the real diversity in evolution has been small-scale. We large things are just flukes — an interesting side branch.

Disassemble the cells of a sponge (by passing them through a sieve, for instance), then dump them into a solution, and they will find their way back together and build themselves into a sponge again. You can do this to them over and over, and they will doggedly reassemble because, like you and me and every other living thing, they have one overwhelming impulse: to continue to be.