MOST OF US HAVE BEEN STUCK IN A traffic jam on a motorway. Sometimes the vehicles move forward slowly, only to come to a halt again a few metres farther on. At other times they go faster for a greater distance only to come to a halt again. And very often, when you're released from this stop-go routine to travel freely to the maximum speed limit, there's not even a sign of a crash or road works. The road-vehicle system has simply got too much traffic in it.
Animal and plant evolution in the Earth-life system works a little bit like this. Each forward movement represents the origin and diversification of a new species or other group. Each brake to a halt is an extinction. The system is in control of itself; and the freedom of movement is connected with the interaction of the vehicles on the packed motorway; groups of organisms in a restricting environment. Observations of the timing and scale of stop-go on road-vehicle systems, and of the time of origin and extinction of animals and plants on the Earth-life system, reveal identical mathematical patterns. They are both self-organised and the progress of each system is controlled from within.
Of course, when there is a crash on the motorway the jam is often so bad that you may stop for hours or even be diverted. When meteorites hit the Earth in the distant geological past, the catastrophe resulted in mass extinctions. More than half the planet's species were lost in the biggest such event 250 million years ago, and all the dinosaurs became extinct through another event at the end of the Cretaceous, 65 million years ago. But each time it happens the system recovers. After a motorway jam the traffic starts to flow freely again. When dinosaurs became extinct there were countless opportunities for new groups of organisms to evolve. Out of disaster came new growth; for mammals to be able to flourish and diversify it was essential for dinosaurs to become extinct.
I work with a small group of young computer scientists who help find these events in large databases of information from evolutionary biology. For example, over recent years palaeontologists have made large databases of the times of the first and last appearances of extinct groups of animals and plants. Others give the locations where each fossil species has been found, along with the geological age of the specimens. The mathematical and statistical analyses that we perform on this data reveals interesting trends within the changing diversity on the planet through geological time. They are the same patterns that come from an analysis of the traffic movements on the busy motorway. Life on planet Earth appears to be in control of itself.
Two distinct kinds of pattern emerge from simple manipulations of the data. First, when the numbers of families of all animals and plants are plotted against time, we get an exponential curve. Further extinctions stop this trend rising to the near-vertical so that the point of infinite diversity will never be reached. If it were to happen then all life would stop; there would be too many families on the limited space of the planet. Overall, the number of origins exceeds the number of extinctions, so biodiversity has been continuing to increase. To stop it getting out of proportion to the limited space the planet provides, the occasional mass extinction event becomes an important part of the evolutionary process.
This new theory of how evolution progresses is opposed to the most widely accepted theory of how evolution moves forward, which is known as Punctuated Equilibrium. It is the idea of evolutionary scientist Stephen Jay Gould and palaeontolgist Niles Eldredge, and supposes that evolution happens in sudden waves of fast change. Between these episodes there is thought to have been quiet passivity. Their theory predicts that the evolution of all animals and plants moved up in a step-wise pattern, with extinctions being promoted at each step-like change. …