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.

But what is life to a lichen? Yet its impulse to exist, to be, is every bit as strong as ours — arguably even stronger. If I were told that I had to spend decades being a furry growth on a rock in the woods, I believe I would lose the will to go on.