WHEN what is now the iconic emblem of extinction finally kicked the bucket, nobody noticed. At that time 鈥� around 1662, probably the year a dodo was last seen in the wild 鈥� the idea that entire species could be wiped out had never occurred to anyone. Pre-Darwinian biology was in thrall to the idea that animals and plants were perfect and eternal designs of the Creator.
Disbelief certainly greeted French naturalist Georges Cuvier in 1796 when he suggested that mammoth, mastodon and giant sloth bones were remains of animals that had died out. Nonsense, snorted the establishment: they were simply living animals that had moved elsewhere. It took time for Cuvier鈥檚 killer argument 鈥� that if these huge beasts were still around, someone would have seen them 鈥� to win out.
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Where there is life, there is extinction. The fossil record tells us that more than 99 per cent of species that have ever lived are no longer with us. Biologists estimate a 鈥渂ackground rate鈥� of about one extinction per million species per year, caused by disease, predation, environmental change and things simply evolving into other things.
More dramatic are five mass extinctions documented in the fossil record. During each, more than three-quarters of the planet鈥檚 species were lost in just a million years or so 鈥� most recently around 66 million years ago, in the event that did for the dinosaurs.
Documenting extinction today is trickier. The International Union for Conservation of Nature defines a species as extinct when there is no reasonable doubt it is no longer alive. The most recent recipient of this dubious honour is the Bramble Cay mosaic-tailed rat (Melomys rubicola), a rodent endemic to a tiny dot of land in the Torres Strait just off Papua New Guinea. Last seen in 2009, it was declared extinct in 2015 after three fruitless surveys of a flat, featureless island about the size of five football pitches.
It is still possible it isn鈥檛 dead, just hiding, perhaps somewhere on the Papua New Guinean mainland. Numerous 鈥淟azarus鈥� species thought extinct exist. The most famous is the coelacanth, a fish thought to have died out with the dinosaurs. It was rediscovered in 1938 swimming around off the east African coast.
The difficulties mean biologists have created categories of quasi-extinction that precede (or not, if conservation succeeds) the final curtain. One is extinct in the wild, when individuals still exist in captivity. Another is functional extinction, when so few members of a species exist it is doomed to extinction.
Human activities have certainly hugely increased the background rate of extinction, by as much as 1000 times. But is what鈥檚 gone gone? The concept of 鈥渄e-extinction鈥� has been doing the rounds lately: using molecular biology to bring a species back. No one has come close yet. 鈥淧eople speculate about a lot of things: dinosaurs, mammoths, dodos. But de-extinction is complicated,鈥� says Beth Shapiro at the University of California, Santa Cruz. If they succeed, extinction may well itself be declared extinct.
Cutting-edge science throws up all sorts of controversial, nebulous and mind-bending concepts. Here鈥檚 your guide to how to think about some of the fiddliest of them:
- In the quantum world, uncertainty reigns 鈥� or is it all in the mind?
- Think you understand how evolution works? You鈥檙e probably wrong
- Why information could be our route to the universe鈥檚 deepest secrets
- Who do you think you are? Why your sense of self is an illusion
- Homo sapiens? Genetic insights suggest we may not really be a species
- Big bang retold: The weird twists in the story of the universe鈥檚 birth
- Firms and governments use the internet to spy on us. Should we care?
- D鈥檕h! Why human beings aren鈥檛 as intelligent as we think
- No more goody two shoes: Why true altruism can鈥檛 exist
- Alien life could be weirder than our Earthling brains can ever imagine
- Why it鈥檚 time to call time on the 鈥榥ature vs nurture鈥� debate
- Dark energy: Understanding the mystery force that rules the universe
