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the daily mail comes late to the pig-ape hybridisation idea

In posting an item about the 'pig-ape hybridisation' suggestion for human origins, the Daily Mail is a) coming rather late to the story (a slow day in the newsroom, perhaps?) and b) showing more regard for sensationalism than for good investigative journalism.

The story's one I've posted about before (& I've reposted my original piece below). Seeing it again really makes me think that the originator of this particular idea is trying to have it both ways. If our morphology is as similar as he claims to that of pigs, and different from chimps, then the differences should show up in our genes. Yet they don't; genetically we are much closer to chimps than to swine. He claims that this can be explained by repeated back-crossing with early humans - which is effectively no more than special pleading (& conveniently ignores the issue of significant differences in chromosome number between the two taxa). 

 

The internet is a wondrous place: a source of information, of amusement, and - alarmingly often - of material that elicits a combination of 'say what?' and <head-desk>. And a hat-tip to PZ Myers for this particular example...

For it has been proposed (by the originator of this particular hypothesis, & further discussed on phys.org) that humans arose as the result of an interspecies hybridisation event, rather than the current model for human evolution that sees chimps and humans sharing a Last Common Ancestor 5-6 million years ago and following their own trajectories since that time.

The event? Hybridisation between great ape (specifically, chimpanzee) & wild boar.

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Now, we know that hybridisation happens; that the 'biological species concept' is not an absolute. But these events are generally between reasonably-closely related species: hybridisation is quite common in the waterfowl, for example. But even in birds, where hybridisation is well-documented, it doesn't appear to cross the lines between one taxonomic order and another. Yet the 'pig+ape' suggestion requires hybridisation between different taxonomic orders - orders that (so fossil & genetic evidence tell us) have been separate for between 79 & 87 million years.

Surprisingly, Dr McCarthy, a geneticist and the proponent of this novel hypothesis, doesn't present much in the way of genetic data to support it. He does agree that, genetically, we are closer to chimpanzees than to any other mammal, but suggests that this is due to back-crossing (with the chimp parent) after the initial hybridisation event:

And why might one suppose that humans are backcross hybrids of the sort just described? Well, the most obvious reason is that humans are highly similar to chimpanzees at the genetic level, closer than they are to any other animal. If we were descended from F1 hybrids without any backcrossing we would be about halfway, genetically speaking, between chimpanzees and whatever organism was the other parent. But we're not. Genetically, we're close to chimpanzees, and yet we have many physical traits that distinguish us from chimpanzees.

Surely the simpler explanation - that we are genetically similar to chimps because we are sister species - is more likely. Especially since at least some of the differences between the two species can be explained by differences in timing of developmental stages (the relative proportions of face & skull, for example), which may be sheeted home to mutations in regulatory portions of the genome. 

In addition, there are major differences both in chromosome number (38 in pigs, 46 in humans) and in the position of various genes on those chromosomes that would make successful gamete production in any hybrid unlikely in the extreme (always supposing the hybrid was actually viable) - PZ discusses this in more length.

But anyway, what about those physical traits that "distinguish us from chimpanzees" & supposedly reflect our shared heritage with pigs? There's a long list here. Many of them relate to bipedalism; to me, it's special pleading to suggest that (for example) the presence of large gluteal muscles in bipedal humans and in domestic pigs is evidence of a close evolutionary relationship (Animal Farm aside, there is a distinct lack of evidence for bipedal locomotion in suids - and strong evidence of selective breeding for large backsides in pigs destined to become bacon & pork). Hairlessness? Only in domestic pigs; anyone who's watched a huntin'&fishin' show on TV will have seen how hairy a wild boar is. Pigs & humans both have longer hind-limbs than forelimbs, & shorter digits (compared to chimps)? Well, ye-es, I guess so, but that's hardly evidence for a close relationship; one could say the same of mice... Similarly, while humans & pigs may (usually) be particular about where they defecate, well, so are other animals; rabbits, anyone? As for "snuggling [snuggling???], tears, alcoholism "being shared features in humans & pigs but not chimps... chimps & humans both have an enzyme (alcohol dehydrogenase 4) that allows us to break down ethanol, and it seems that chimps can become addicted to alcohol if given the opportunity.

Also offered in evidence are those diseases which are rare in non-human primates: "heart attack, atherosclerosis, and cancer (melanoma)". Since these are to some degree, age-related, their relative rarity (for they are not absent in apes) may be ascribed to differences in lifespan: chimps in the wild may not live long enough to develop them.

Annoyingly, I see that over at uncommondescent, this proposal has been presented as even more evidence that evolutionary biologists are Getting It Wrong!

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Perusing more of the macroevolution website, I found the suggestion that armadillos and pangolins evolved from ankylosaurs and stegosaurs (page 244 at that link). It would be interesting to hear a palaeontologist's taken on that one, but the fact that dinosaurs had diapsid skulls while mammals are synapsid doesn't help. 

 
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5 Comments

I found the suggestion that armadillos and pangolins evolved from ankylosaurs and stegosaurs (page 244 at that link).

His argument seems to be that ankylosaurs and stegosaurs were actually mammals all along, mistakenly classified as 'dinosaurs' because of DOGMA (rather then, for instance, because of the structure of their skulls & pelves). So it is not so much a question of them evolving into armadillos and pangolins; instead, fossils from before the K-T boundary are labelled "ankylosaur", and ones after the boundary are labelled "armadillo", because DOGMA.

On a hunch I looked up "cetacean" in his PDF. Sure enough, the search for the terrestrial mammalian ancestors of cetaceans turns out to be misguided.* In fact their true forebears were in front of our eyes all along; mosasaurs were cetaceans.

This sort of thing is very hard to satirise.

*He points out that the various fossils nominated for this place in the evolutionary tree don't look anything like cetaceans -- they have four legs! And they're terrestrial!

Yes, I enjoyed your take on it (& took the liberty of spreading it around on FB)

Problem was because you couldn't/didn't take the idea seriously to begin with, you didn't read his argument with adequate focus, which left you at risk of constructing a rebuttal that wasn't aimed at the right argument. Which is what you did. All your other objections were misconceived also.

Now a Chinese/American study of the pig/human genome has found significant regions of common dna. This on the back of two other papers in the last three month that present evidence for inexplicable commonalities.

All of that said, your tone was reasonable and you treated McCarthy with respect where most everyone else at the time derided and mocked him.

I would make a stranger-promise to you, that should you give up the hour or so of topmost best quality time to reading his evidence and argument. You'll not regret it. And you'll agree I should think, that from a dispassionate scientific POV, his theory is much stronger than any other including incumbent.

p.s. one of your original arguments was human/chimps as sister species was the simpler explanation. The basis of his argument, was that humans share a long list of traits with chimps/apes. But there is a shorter but substantial list of traits that humans alone manifest. And in every single instance of that, the trait is shared with pigs, and the morphology of the trait is half way between humans and pigs.

He rules out convergent evolution with corresponding bones from contemporary humans and pigs respectively. high resolution blow-ups of the microscopic bumps and lumps on the surface of bone - the tiny imperfections that occur randomly with genetic drift, are clearly the same.

Anyway, the proof is beginning to hit the fan now - the otgher reason to have another look

We have significant areas of DNA homologies with fruit flies, but no-one is suggesting a hybridisation event there.
In addition, why on earth would you expect a trait to be half-way between humans & pigs, as evidence of shared ancestry? This suggests a lack of understanding around the nature of any Last Common Ancestor.
"Anyway, the proof is beginning to hit the fan now - the otgher reason to have another look" - Homo naledi, anyone?

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Recent Comments

  • Alison Campbell: We have significant areas of DNA homologies with fruit flies, read more
  • Chris Mannering: Problem was because you couldn't/didn't take the idea seriously to read more
  • Alison Campbell: Yes, I enjoyed your take on it (& took the read more
  • herr doktor bimler: Now look what you made me do. read more
  • herr doktor bimler: I found the suggestion that armadillos and pangolins evolved from read more