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How to think about… SPECIES
HOW TO THINK ABOUT…
SPECIES
Attempts to divide nature into neat units throw up intractable controversies, including possibly in our own evolutionary history
HOW TO THINK ABOUT… It certainly wasn’t big, and it probably didn’t bang – and the surprising twists in the story of how it all began don’t end there
At some point, they become so distinct that we classify them as separate species. It just isn’t easy to pin down exactly when. We could just accept that “species” is a fluid, imperfect concept that helps us understand and conserve the diversity of the natural world. Unfortunately, it doesn’t always. This year, for example, genetic analysis of the world’s largest amphibian,
EYE VISION/ALAMY STOCK PHOTO
H
OMO SAPIENS likes to categorise. Putting things in boxes helps us understand the complexities of the world around us – until it doesn’t. Take the apparently simple organising principle of a species. You might have learned at school that a species is a group of individuals that can breed to produce fertile offspring. But this is just one of at least 34 competing definitions concocted over the past century by researchers working in different fields. Ecologists tend to categorise based on lifestyle. Palaeontologists focus on form. Geneticists sequence genomes and then create family trees based on shared, genetically encoded characteristics. The problem is that evolution – the origin of species – is intrinsically about gradual, random change (see “How to think about... evolution”, page 36). Charles Darwin recognised that organisms live in populations that can diverge and evolve in different directions, especially if they face different environmental challenges.
SPECIES
the critically endangered Chinese giant salamander, revealed it was actually three species, not one, each requiring different conservation interventions. Traditional species concepts are further undermined by high levels of hybridisation in nature. One prominent example is the critically endangered red wolf found in the south-east US, which is now thought to be a cross between a coyote and a grey wolf. Our species isn’t immune to these confusions. In recent years, we have discovered that our ancestors interbred with other hominins, including Neanderthals, Denisovans and a mysterious “species X”. Does this make us hybrids, or does it mean those hominins weren’t separate species, but simply different versions of us? There probably isn’t a clear answer to such questions. In the end, the whole idea of fixed species appeals to ideas of immutability in nature that now seem rather outdated. Biology is messy, and doesn’t bend to our desire for clean classifications. Kate Douglas
SPECIES The Chinese giant salamander: one species or three?
THE BIG BANG
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05
HATEVER you do, don’t ask where it happened. “The most common misconception is that the big bang was an explosion in a particular place,” says William Kinney, a cosmologist at the University at Buffalo in New York. “That’s just completely wrong.” The best evidence for the big bang is all around us in the cosmic microwave background, the radiation released once the universe had cooled sufficiently for atoms to form, when it was about 380,000 years old. And that is the point: everywhere in today’s universe was where the big bang was. “It’s not something that
happened somewhere, but something that happened everywhere, including the space you happen to be occupying now,” says Dan Hooper at Fermilab in Illinois. When cosmologists talk about the big bang, they are talking about an extremely dense, hot state that existed around 13.8 billion years ago and which has since expanded and cooled to make the universe we know today. Extremely dense and hot – but not infinitely so. The idea that the universe was created from an infinitesimal speck, known as the big bang “singularity”, comes from winding the showreel of an expanding, cooling universe
06
backwards and not stopping until we get to a beginning. But, unfortunately, our current theories of physics can’t deal with space and time on such unfathomably small scales. So we can say nothing sensible about the moment when the universe was a single point, if indeed it ever happened. “We may just have to come to terms with that,” says Kinney. However it all started, the big bang that followed wasn’t so much an explosion, which implies stuff flying off randomly, but a perfectly uniform expansion – albeit one that seems to have been, in its first throes at least, unimaginably > 14 December 2019 | New Scientist | 39
SPECIES
Attempts to divide nature into neat units throw up intractable controversies, including possibly in our own evolutionary history
HOW TO THINK ABOUT… It certainly wasn’t big, and it probably didn’t bang – and the surprising twists in the story of how it all began don’t end there
At some point, they become so distinct that we classify them as separate species. It just isn’t easy to pin down exactly when. We could just accept that “species” is a fluid, imperfect concept that helps us understand and conserve the diversity of the natural world. Unfortunately, it doesn’t always. This year, for example, genetic analysis of the world’s largest amphibian,
EYE VISION/ALAMY STOCK PHOTO
H
OMO SAPIENS likes to categorise. Putting things in boxes helps us understand the complexities of the world around us – until it doesn’t. Take the apparently simple organising principle of a species. You might have learned at school that a species is a group of individuals that can breed to produce fertile offspring. But this is just one of at least 34 competing definitions concocted over the past century by researchers working in different fields. Ecologists tend to categorise based on lifestyle. Palaeontologists focus on form. Geneticists sequence genomes and then create family trees based on shared, genetically encoded characteristics. The problem is that evolution – the origin of species – is intrinsically about gradual, random change (see “How to think about... evolution”, page 36). Charles Darwin recognised that organisms live in populations that can diverge and evolve in different directions, especially if they face different environmental challenges.
SPECIES
the critically endangered Chinese giant salamander, revealed it was actually three species, not one, each requiring different conservation interventions. Traditional species concepts are further undermined by high levels of hybridisation in nature. One prominent example is the critically endangered red wolf found in the south-east US, which is now thought to be a cross between a coyote and a grey wolf. Our species isn’t immune to these confusions. In recent years, we have discovered that our ancestors interbred with other hominins, including Neanderthals, Denisovans and a mysterious “species X”. Does this make us hybrids, or does it mean those hominins weren’t separate species, but simply different versions of us? There probably isn’t a clear answer to such questions. In the end, the whole idea of fixed species appeals to ideas of immutability in nature that now seem rather outdated. Biology is messy, and doesn’t bend to our desire for clean classifications. Kate Douglas
SPECIES The Chinese giant salamander: one species or three?
THE BIG BANG
W
05
HATEVER you do, don’t ask where it happened. “The most common misconception is that the big bang was an explosion in a particular place,” says William Kinney, a cosmologist at the University at Buffalo in New York. “That’s just completely wrong.” The best evidence for the big bang is all around us in the cosmic microwave background, the radiation released once the universe had cooled sufficiently for atoms to form, when it was about 380,000 years old. And that is the point: everywhere in today’s universe was where the big bang was. “It’s not something that
happened somewhere, but something that happened everywhere, including the space you happen to be occupying now,” says Dan Hooper at Fermilab in Illinois. When cosmologists talk about the big bang, they are talking about an extremely dense, hot state that existed around 13.8 billion years ago and which has since expanded and cooled to make the universe we know today. Extremely dense and hot – but not infinitely so. The idea that the universe was created from an infinitesimal speck, known as the big bang “singularity”, comes from winding the showreel of an expanding, cooling universe
06
backwards and not stopping until we get to a beginning. But, unfortunately, our current theories of physics can’t deal with space and time on such unfathomably small scales. So we can say nothing sensible about the moment when the universe was a single point, if indeed it ever happened. “We may just have to come to terms with that,” says Kinney. However it all started, the big bang that followed wasn’t so much an explosion, which implies stuff flying off randomly, but a perfectly uniform expansion – albeit one that seems to have been, in its first throes at least, unimaginably > 14 December 2019 | New Scientist | 39