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How to think about… EXTINCTION
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HOW TO THINK ABOUT…
EXTINCTION
The fossil record tells us that species go extinct all the time. The big problems come in pinning down how and when that happens – and the part we play in it
W
HEN what is now the iconic emblem of extinction finally kicked the bucket, nobody noticed. At that time – around 1662, probably the year a dodo was last seen in the wild – 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’s killer argument – that if
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HOW TO THINK ABOUT…
these huge beasts were still around, someone would have seen them – to win out. 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 “background rate” 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’s species were lost in just a million years or so – 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 mosaictailed 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’t dead, just hiding, perhaps somewhere on the Papua New Guinean mainland. Numerous “Lazarus” 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.
ALTRUISM
If only the fittest survive, why would someone do good deeds for no payback? This enduring mystery goes to the heart of how evolution does – and doesn’t – work
T
HERE was no doubt that the humpback whale saved the seal’s life, carrying it away on its chest and protecting it with its flipper from the onslaught of the killer whales. It was odd behaviour that marine ecologist Robert Pitman observed in the frigid Antarctic seas back in 2009 – but, it turned out, not uncommon. How you interpret it goes to the heart of an intense 42 | New Scientist | 14 December 2019
evolutionary debate: can any creature ever be truly altruistic? A basic reading of evolution says no, because survival of the fittest means maximising your own reproductive success. Altruism, defined by philosopher Auguste Comte in 1851 as “intentional action, ultimately for the welfare of others, that entails at least the possibility of either no benefit or a loss to the
actor”, is simply not a thing. Things that look like it are widespread. Many animals act in ways that reduce their own reproductive success but benefit others. Some social insects, for example, give up reproduction entirely to support the colony. One proposed explanation is kin selection: altruism persists because it helps the close relatives of nicer
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individuals to reproduce, which passes their own genes on too. Some form of this was probably at play with the humpback whale: by automatically chasing away orcas, regardless of what they were attacking, the humpback increased the survival chances of individuals in its pod. David Sloan Wilson at Binghamton University in New York champions a different idea: group selection. This emphasises the reproductive success not of individuals, but of a whole group. “All you have to do is go up a little bit in scale, and there you have your evolutionary advantage,” he says. Wilson and his colleagues have done experiments with groups of insects called pond skaters that he says back up this idea. Male pond
HOW TO THINK ABOUT…
EXTINCTION
The fossil record tells us that species go extinct all the time. The big problems come in pinning down how and when that happens – and the part we play in it
W
HEN what is now the iconic emblem of extinction finally kicked the bucket, nobody noticed. At that time – around 1662, probably the year a dodo was last seen in the wild – 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’s killer argument – that if
10
HOW TO THINK ABOUT…
these huge beasts were still around, someone would have seen them – to win out. 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 “background rate” 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’s species were lost in just a million years or so – 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 mosaictailed 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’t dead, just hiding, perhaps somewhere on the Papua New Guinean mainland. Numerous “Lazarus” 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.
ALTRUISM
If only the fittest survive, why would someone do good deeds for no payback? This enduring mystery goes to the heart of how evolution does – and doesn’t – work
T
HERE was no doubt that the humpback whale saved the seal’s life, carrying it away on its chest and protecting it with its flipper from the onslaught of the killer whales. It was odd behaviour that marine ecologist Robert Pitman observed in the frigid Antarctic seas back in 2009 – but, it turned out, not uncommon. How you interpret it goes to the heart of an intense 42 | New Scientist | 14 December 2019
evolutionary debate: can any creature ever be truly altruistic? A basic reading of evolution says no, because survival of the fittest means maximising your own reproductive success. Altruism, defined by philosopher Auguste Comte in 1851 as “intentional action, ultimately for the welfare of others, that entails at least the possibility of either no benefit or a loss to the
actor”, is simply not a thing. Things that look like it are widespread. Many animals act in ways that reduce their own reproductive success but benefit others. Some social insects, for example, give up reproduction entirely to support the colony. One proposed explanation is kin selection: altruism persists because it helps the close relatives of nicer
*
individuals to reproduce, which passes their own genes on too. Some form of this was probably at play with the humpback whale: by automatically chasing away orcas, regardless of what they were attacking, the humpback increased the survival chances of individuals in its pod. David Sloan Wilson at Binghamton University in New York champions a different idea: group selection. This emphasises the reproductive success not of individuals, but of a whole group. “All you have to do is go up a little bit in scale, and there you have your evolutionary advantage,” he says. Wilson and his colleagues have done experiments with groups of insects called pond skaters that he says back up this idea. Male pond