Michael Boulter has an intriguing tale to tell. From analysis of a huge database of fossil remains, he and his colleagues have found a characteristic pattern to the evolution of life. Just as individual species exist for only a finite time, so the larger groups, the families to which species belong, do not last forever. Typically, the number of families of a particular kind starts small, rises to a peak and then tails off.
What makes this of more than academic interest is evidence that the number of families of mammals has passed its peak and will soon decline to zero. To a geologist, "soon" means within the next few tens of millions of years; but since we are mammals, the story still strikes close to home.
It strikes even closer to home when Boulter explains that the rate at which mammal species are disappearing began to increase a few tens of thousands (not millions) of years ago and that the Earth is now experiencing a "mass extinction" comparable to the event that killed off the dinosaurs 65 million years ago and opened the way for the rise of mammals.
This ought to make for a gripping read; but Boulter does not tell the story very well. He has a tendency to get bogged down in details, and there is far too much about the work of his own team and not enough of the broader picture. When he does move out of the area of his specialist expertise as a palaeobiologist, he often stumbles, displaying a poor grasp of astronomy, getting the mechanics of greenhouse warming wrong and completely misunderstanding one of the key features of Jim Lovelock's Gaia hypothesis.
This particular cobbler is better when he sticks to his own last. With everything else stripped away, the interesting and exciting new aspects of his story amount only to enough for a healthy article in a magazine such as Scientific American.
Some of the more familiar aspects, already dealt with in several books over the past decade, are well worth repeating here. There is still not the widespread appreciation that they deserve. The work of Boulter and his colleagues is set in the context of the idea of "self-organised criticality", which is most simply understood in terms of grains of sand falling on a flat table to make a pile. As the grains drop one by one, the pile gets steeper, until at some critical point the addition of a single grain causes it to slump in a series of landslides. Then there is a period of quiescence while sand builds up again to the critical point.
There is now a compelling weight of evidence that living networks – ecosystems – operate in a similar way, with the fine-tuning of individual species by evolution gradually building up a kind of evolutionary tension in the network. The tension may be released by a tiny trigger (perhaps the extinction of a single species), leading to the collapse of the network, with many species becoming extinct. This has led to a new understanding of how evolution works, with the slow process of Darwinian evolution by natural selection punctuated by mass extinctions. One key insight is that extinctions of all sizes may result from small triggering events, with no correlation in size between the trigger and the extinction.
Which brings us back to the extinction we are living through. Although there is good evidence that the death of the dinosaurs was triggered by a meteorite, there is no such large outside event to blame for what's happening now. Instead, Boulter blames a small internal effect – human activity, ranging from wiping out mammoths by hunting to polluting the planet with greenhouse gases. It is, indeed, a story worth telling, and – despite its flaws – a book worth reading. It should give pause to all those who talk glibly of a far distant future in which humankind spreads out from Earth to conquer the stars. In 65 million years, there may be intelligent life on Earth and scientists who study extinction events in the fossil record. But all the evidence suggests they will not be mammals, let alone humans.
The reviewer is visiting fellow in astronomy at the University of SussexReuse content