The earliest was during the late Ordovician period, 450 million years ago, when glaciation wreaked havoc. The worst was at the end of the Permian period, 250 million years ago, when perhaps 90 per cent of species were wiped out. The most recent came at the end of the Cretaceous period and was terrible news for the dinosaurs.
Are we in the throes of a sixth catastrophe? In her passionate and frequently terrifying book, Elizabeth Kolbert suggests that we are. Extinction is a constant in the natural world but it tends to be a rather leisurely business. There is always something called ‘background extinction’, for which Kolbert gives us the mammalian maths. If there are roughly 5,500 mammal species today, then we could expect normal processes to make one of them disappear every 700 years or so.
Mass extinction is a different affair – species vanish at a faster rate, and there are signs that this is happening now. Amphibians appear to be among the most vulnerable and, on some accounts, the extinction rate is many thousands of times higher than the norm. Similarly devastating igures apply to other branches of the world’s lora and fauna.
The major difference this time is the culprit. Previously, climate, naturally induced rises or reductions in CO2 levels, or large asteroids were to blame. The sixth mass extinction is largely down to the mischief of humanity.
Perhaps we shouldn’t be surprised. Kolbert reminds us that the track record of Homo sapiens isn’t particularly cheering. Long ago, we put an end to the Neanderthals, although apparently not before mating with them (there’s a little Neanderthal in all of us), and when we encountered the great auk, we destroyed a species that numbered in the millions out of hunger and a need for ish bait and feathers for our mattresses.
Kolbert writes, ‘Though it would be nice to imagine there once was a time when man lived in harmony with nature, it’s not clear that he ever really did.’ The disappearance of the megafauna tens of thousands of years ago coincided with the arrival of human settlement. A causal link hasn’t been found, but if one were a betting man…
Perhaps, then, the so-called Anthropocene era is older than we might imagine, but it has certainly caused greatest havoc over the past two, post-industrial centuries. There are all sorts of threats. Acidification of the oceans is near the top of the list. It does great damage to the availability of nutrients, it’s a boon to toxic algae, and creatures that are unable to adapt or regulate their internal chemistry are placed in serious jeopardy.Pity, then, the calciiers, which build their shells or external skeletons from calcium carbonate. Pity, thus, the coral reefs.
One of the great dangers faced by so many species is the introduction of foreign interlopers, and humanity has done a great deal to destroy the norms of how plants and animals are geographically distributed. It has been found that in some parts of the world, introduced plants outnumber native ones and that, in a given 24-hour period, up to 10,000 species are present in ballast water.
Kolbert has also travelled far and wide, and she gives fascinating accounts of her encounters with scientists around the globe – from those studying golden frogs in Panama to those who keep an eye on Peruvian trees. We discover ‘the excitement of what’s being learned as well as the horror of it’.
It’s surprising to discover how long it took us to accept the concept of extinction, although the remains of American mastodons set mental cogs in motion during the 18th and early 19th centuries. And it’s interesting to read about how extinction plays fast and loose with the normal rules and expectations of evolution. When the crisis hits, it doesn’t matter how well adapted a species is or how bright its future seems.
Kolbert isn’t a doom-monger, although there’s more than enough doom at her disposal. Rather, she offers a nuanced, detailed summary of the state we’re in and encourages us to do better. Who could disagree?
THE SIXTH EXTINCTION: An Unnatural History by Elizabeth Kolbert, Bloomsbury, £20