Despite a new hypothesis, and the evidence of George Orwell's eyes in
Animal Farm, humans were not the outcome of a curious hybridisation
between pigs and chimps
When confronted with stories in the Daily Nimbyist Bungaloid Curtain-Twitcher
I murmur words such as 'this', 'touch', 'with', 'don't' and
'bargepole'. However, when alerted to the following gem by my
correspondent B. C. of Swindon, I really had to investigate. The
headline is enough to make one gasp and stretch one's eyes:
'Humans evolved after a female chimpanzee mated with a pig': Extraordinary claim made by American geneticist
it reads.
And, yes, it means precisely what you think it means. It's not one of those headlines in which compression creates whole new universes of possibility, such as
Eighth Army Push Bottles Up Germans
or, more pertinently
Scientists Make Gorillas Pregnant
As all three of you will be aware by now, I am mildly interested in the field of human origins, and, in particular, the way this subject is routinely misinterpreted by armchair scientists and the popular prints. Indeed, I have just published a book on that very subject. It's called 'The Accidental Species' and appositely subtitled 'Misunderstandings of Human Evolution'. It's available in the proverbial All Good Bookshops and would make the ideal festive gift for the science geek in your life.
But I digress.
To be fair to the Daily Immigrants Cause Cancer, their piece was balanced, in that it not only included a link to the website of Dr Eugene McCarthy, the geneticist who proposed this unusual idea, but also to a magisterial refutation by P. Z. Myers on his blog Pharyngula.
I hope that in the following précis I am not misrepresenting Dr McCarthy's ideas. In short – if I have it right – he proposes that many years ago, a chimpanzee had carnal relations (look, there's no easy way to say this in a family newspaper) with a pig. And, not only did it have carnal relations, but its union was blessed with issue. By dint of extensive backcrossing between chimps and the F1 hybrid (yes, the piece does include scientific words like 'backcrossing' and 'F1 hybrid') you'd get a chimpy sort of thing with variously piggy features, which came eventually to look like a human being. Simples.
Dr McCarthy supports this hypothesis with a cloven-hoofed approach (did I say 'cloven-hoofed'? I mean 'two-pronged').
The first is to say that hybridization has been much more important in the origin of species than usually assumed. Plants do it all the time. It is rarer in animals, though there are plenty of hybrids between animals which belong to different species, and occasionally between different genera, and some of these hybrids are fertile. In those far-off days when I was a doctorate student, I had to tell the difference between the very similar bones of cows (genus Bos) and bison (genus Bison), individuals of which can occasionally interbreed. And if I had a pound for every time someone asked me how I tell the difference between a buffalo and a bison (you can't wash your hands in a buffalo), I'd have £874. Hybridization between chimp and pig, though, is a much bigger stretch. It requires interbreeding between separate orders of mammal. Chimps are primates, and pigs are artiodactyls (even-toed ungulates). Despite McCarthy's suggestions to the contrary, reports of hybrids between different orders of mammal, though, are, literally, incredible. His suggestion that the platypus is the result of hybridization between mammals and birds – an even bigger ask – seems to rest on a misunderstanding of the inheritance of chromosomes. Although some of the genetics of platypuses seems birdlike, this is much more consistent with its primitive state, and a mark of a shared inheritance between birds and reptiles (preserved in primitive mammals) than direct evidence for miscegenation.
The second is a long list of features we see in pigs which seem to be shared, perhaps uniquely, with humans. These include features of the skin, including relative hairlessness and high fat content; features of the face, including eyebrows, heavy eyelashes and lightly pigmented eyes; a large number of skeletal features perhaps suggestive of a shared bipedal ancestry; a pot-pourri of physiological and cranial attributes, and even some shared features of behaviour, including swimming, extended copulation time, and alcoholism.
If some of this sounds familiar, it should, because it is reminiscent in some ways of the Aquatic-Ape hypothesis, concerning which I wrote in this column a while back.
The Chimp-Pig Hypothesis (P. Z. Myers' name for it is a good deal saltier) resembles the Aquatic Ape hypothesis in that it takes some initial idea, or insight, and then cherry-picks the evidence it needs, from wherever it can, to support it, and discounts anything with which it disagrees.
The biggest counter to the idea is, simply, evolutionary history. The last common ancestor of pigs and people was in all likelihood a small furry creature that lived around 80 million years ago, since when our courses have taken very different turns. Any similarities we have are likely to be relics of our common ancestries; convergences we've independently picked up later; or results of the vicissitudes of Dame Fortune. That pigs provide heart valves that work perfectly well in humans is not evidence of common ancestry – no more than the fact that the only creature other than humans that suffers from leprosy is an armadillo makes us close relatives of that creature.
Despite reports that human flesh tastes like pork, and that the pidgin for human meat might or might not be 'long pig', ultimate insight comes from the study of genomes. The analysis of the pig genome, published in Nature last year and available free does reveal shared similarities with humans – and why not? It shares similarities with many other mammals, too. But there seems no especially close relationship between the pig genome and the human genome, which is what one would expect had some hybridization occurred in the past few million years. The proof of the (black) pudding isn't in the eating.
And if none of that convinces, ask yourself this moral conundrum. If you were a pig, would you actually want to be related to us? As it's the festive season I might get away with some traditional piggeral on this subject, before I wish you and yours a happy Solstice/Hannukah/Christmas/Festival of the Execration of Bakrug the Great Water Lizard (delete as applicable) and a healthy and wealthy New Year:=
Henry Gee is a Senior Editor of Nature but writes here in a personal capacity.
'Humans evolved after a female chimpanzee mated with a pig': Extraordinary claim made by American geneticist
it reads.
And, yes, it means precisely what you think it means. It's not one of those headlines in which compression creates whole new universes of possibility, such as
Eighth Army Push Bottles Up Germans
or, more pertinently
Scientists Make Gorillas Pregnant
As all three of you will be aware by now, I am mildly interested in the field of human origins, and, in particular, the way this subject is routinely misinterpreted by armchair scientists and the popular prints. Indeed, I have just published a book on that very subject. It's called 'The Accidental Species' and appositely subtitled 'Misunderstandings of Human Evolution'. It's available in the proverbial All Good Bookshops and would make the ideal festive gift for the science geek in your life.
But I digress.
To be fair to the Daily Immigrants Cause Cancer, their piece was balanced, in that it not only included a link to the website of Dr Eugene McCarthy, the geneticist who proposed this unusual idea, but also to a magisterial refutation by P. Z. Myers on his blog Pharyngula.
I hope that in the following précis I am not misrepresenting Dr McCarthy's ideas. In short – if I have it right – he proposes that many years ago, a chimpanzee had carnal relations (look, there's no easy way to say this in a family newspaper) with a pig. And, not only did it have carnal relations, but its union was blessed with issue. By dint of extensive backcrossing between chimps and the F1 hybrid (yes, the piece does include scientific words like 'backcrossing' and 'F1 hybrid') you'd get a chimpy sort of thing with variously piggy features, which came eventually to look like a human being. Simples.
Dr McCarthy supports this hypothesis with a cloven-hoofed approach (did I say 'cloven-hoofed'? I mean 'two-pronged').
The first is to say that hybridization has been much more important in the origin of species than usually assumed. Plants do it all the time. It is rarer in animals, though there are plenty of hybrids between animals which belong to different species, and occasionally between different genera, and some of these hybrids are fertile. In those far-off days when I was a doctorate student, I had to tell the difference between the very similar bones of cows (genus Bos) and bison (genus Bison), individuals of which can occasionally interbreed. And if I had a pound for every time someone asked me how I tell the difference between a buffalo and a bison (you can't wash your hands in a buffalo), I'd have £874. Hybridization between chimp and pig, though, is a much bigger stretch. It requires interbreeding between separate orders of mammal. Chimps are primates, and pigs are artiodactyls (even-toed ungulates). Despite McCarthy's suggestions to the contrary, reports of hybrids between different orders of mammal, though, are, literally, incredible. His suggestion that the platypus is the result of hybridization between mammals and birds – an even bigger ask – seems to rest on a misunderstanding of the inheritance of chromosomes. Although some of the genetics of platypuses seems birdlike, this is much more consistent with its primitive state, and a mark of a shared inheritance between birds and reptiles (preserved in primitive mammals) than direct evidence for miscegenation.
The second is a long list of features we see in pigs which seem to be shared, perhaps uniquely, with humans. These include features of the skin, including relative hairlessness and high fat content; features of the face, including eyebrows, heavy eyelashes and lightly pigmented eyes; a large number of skeletal features perhaps suggestive of a shared bipedal ancestry; a pot-pourri of physiological and cranial attributes, and even some shared features of behaviour, including swimming, extended copulation time, and alcoholism.
If some of this sounds familiar, it should, because it is reminiscent in some ways of the Aquatic-Ape hypothesis, concerning which I wrote in this column a while back.
The Chimp-Pig Hypothesis (P. Z. Myers' name for it is a good deal saltier) resembles the Aquatic Ape hypothesis in that it takes some initial idea, or insight, and then cherry-picks the evidence it needs, from wherever it can, to support it, and discounts anything with which it disagrees.
The biggest counter to the idea is, simply, evolutionary history. The last common ancestor of pigs and people was in all likelihood a small furry creature that lived around 80 million years ago, since when our courses have taken very different turns. Any similarities we have are likely to be relics of our common ancestries; convergences we've independently picked up later; or results of the vicissitudes of Dame Fortune. That pigs provide heart valves that work perfectly well in humans is not evidence of common ancestry – no more than the fact that the only creature other than humans that suffers from leprosy is an armadillo makes us close relatives of that creature.
Despite reports that human flesh tastes like pork, and that the pidgin for human meat might or might not be 'long pig', ultimate insight comes from the study of genomes. The analysis of the pig genome, published in Nature last year and available free does reveal shared similarities with humans – and why not? It shares similarities with many other mammals, too. But there seems no especially close relationship between the pig genome and the human genome, which is what one would expect had some hybridization occurred in the past few million years. The proof of the (black) pudding isn't in the eating.
And if none of that convinces, ask yourself this moral conundrum. If you were a pig, would you actually want to be related to us? As it's the festive season I might get away with some traditional piggeral on this subject, before I wish you and yours a happy Solstice/Hannukah/Christmas/Festival of the Execration of Bakrug the Great Water Lizard (delete as applicable) and a healthy and wealthy New Year:=
Twas an evening in September, or maybe 'twas November,
I was rolling down the street in drunken pride,
I came over all aflutter,
And lay down in the gutter,
And a pig came up a lay down by my side.
A lady passing by, my condition did espy
She hurried past, and yet was heard to say
"You can tell a man wot boozes
By the company he chooses."
And the pig got up and slowly walked away.
Henry Gee is a Senior Editor of Nature but writes here in a personal capacity.
