In learning to suck energy from sunlight and in swallowing shocking amounts of oxygen, in heaving up from the beneficent chemical crucible of the sea and in exploring leafy interiors and desiccated desert, life has split into discrete identities, strewn about fresh designs, unimaginably varied feet, teeth, tongues, antennae, wings, leaves, brains. In this world of dreamlike change, the lexicon of genes, like human languages, is thought to evolve along unreturning tracks. We know that nature is constantly making random changes in almost all genes, and that two species that diverged from a common ancestor hundreds of millions of years ago are likely to have accumulated a lot of little alterations. As eons pass, so do variants of genes, vanishing on the same wind that took the tyrannosaurs. Over the last few years I have wandered the body, looking for these legacies and slim continuances, seeking to ferret them out of their holes and sun them a little, to brush their surface in places, give them a stab or pinch them to the bone if I could.
Chimps are one thing, yeast is quite another.
We have for so long picked ourselves out from the horde of other creatures, reckoned ourselves the peak and point of nature's whole history. The physicist Michio Kaku once wrote that finding the key to weather and seasons required a leap into another dimension, up into outer space. Understanding humanity's place in the matrix of life requires just such a leap, but downward, into the diminutive world of genes and cells. Raised as I was on gerbils and birds, on the love of the whole organism, not its microscopic parts, I find it a stretch to descend into the darkness of a molecular world. I know my bats, weasels, and wood frogs far better than I do the crabbed atoms of a hemoglobin molecule.