The Ancestor's Tale: A Pilgrimage to the Dawn of Evolution

by Richard Dawkins

In spite of the fascination of fossils, it is surprising how much we would still know about our evolutionary past without them. If every fossil were magicked away, the comparative study of modern organisms, of how their patterns of resemblances, especially of their genetic sequences, are distributed among species, and of how species are distributed among continents and islands, would still demonstrate, beyond all sane doubt, that our history is evolutionary, and that all living creatures are cousins. Fossils are a bonus. A welcome bonus, to be sure, but not an essential one. It is worth remembering this when creationists go on (as they tediously do) about ‘gaps’ in the fossil record. The fossil record could be one big gap, and the evidence for evolution would still be overwhelmingly strong. At the same time, if we had only fossils and no other evidence, the fact of evolution would again be overwhelmingly supported. As things stand, we are blessed with both.

Incidentally, having said that oxygen is produced by green plants and algae, it is an oversimplification to leave it at that. It is true that plants give off oxygen. But when a plant dies, its decay, in chemical reactions equivalent to burning all its carbonaceous materials, would use up an amount of oxygen equal to all the oxygen released by that plant during its lifetime. There would therefore be no net gain in atmospheric oxygen, but for one thing. Not all dead plants decay completely. Some parts of them are laid down as coal (or equivalents), other parts are consumed and bits of the consumers themselves may become locked into rocks.* The net effect is to store energy-rich compounds underground and leave some oxygen free to circulate. Releasing some of that stored energy by burning fossil fuels turns this oxygen back into carbon dioxide, taking us back towards the ancient status quo. Fortunately we are unlikely to return the atmosphere all the way to our suffocating Canterbury. But we should not forget that the oxygen we breathe exists only because of compounds tied up underground, which include coal and oil. We burn them at our peril.

Not only is life on this planet amazing, and deeply satisfying, to all whose senses have not become dulled by familiarity: the very fact that we have evolved the brain power to understand our evolutionary genesis redoubles the amazement and compounds the satisfaction.