Our overlooked ancestor

Going the whole hog

Perhaps we are related

Hybridisation is now recognised as a significant factor in recent human ancestry when genetically close hominids mated together. Why do we fail to recognise hybridisation has always been an agent in evolution including our own?

Most of us were comfortable with the idea that we shared an ancestor with a monkey. More recent research suggests we are actually descended from a monkey such as an early chimpanzee or a bonobo. Why does the suggestion that the pig might also be a close relation be treated with scorn and derision?

As regular readers know I have no special expertise in genetics. I have always been fascinated by evolution but write merely as an observer of the insights of others. 

I acknowledge how my articles on hybridisation are strongly influenced by the writing of Georgia University geneticist Gene McCarthy. Today my entire article is based on his thinking.

For decades McCarthy has promoted hybridity as a force in evolution. More and more modern geneticists agree and record hybridisation’s contribution to evolution but even now in some quarters it is not fashionable to say so.

It is tragic that a free thinker such as McCarthy ploughs his own furrow without support and little formal recognition. I cannot find any plausible explanation of why his overall hypothesis of the way of evolution is wrong.

You will have to turn to Gene’s blog to check out the details of most of the things I have to say today.You will be impressed with the fine detail and meticulous research he has applied.

As a good scientist McCarthy agrees that the idea that a pig has enriched our genetic inheritance by hybridisation is not proven. I suspect privately he is pretty certain he is right and I think so too.

Superficial evidence of our porcine ancestry

When you look into a pig’s eyes you might be gazing at a beautiful woman. The only primate which shares this feature of narrow eyes, eyebrows and eyelashes is us. Our skin’s share so many similar features and in our skin’s smoothness and lack of hair we are almost unique.

Although genetic theory states that we and the pig are evolutionarily distant, recent research shows we are very much closer than previously thought and the medical establishment is starting to find all kinds of ways of exploiting a general lack of our cells and tissues rejecting each other. Simple features such as heart valves and lenses can already be grafted between us. No genetic distance at all.

We are the only primate with many of pig’s cartilaginous features such as characteristics of our noses and ears. No monkey has anything like our protruding noses which resemble so much more a pig’s rootling snout

At a less pleasant level I might mention some of our odours are very similar and where we permit it a pig’s level of hygiene is high. Historic records of cannibals say that our flesh tastes and smells just the same. Such cannibals called man ‘long pig’. 

One wonders whether ancient man, so much closer to nature, developed still surviving cultural taboos as a result of our similarities.

The BBC recently waxed lyrical about how human eye contact supplemented our language.They explained our expressive white sclera (the whites of our eyes) are unique to humanity.

It is generally regarded that pigs are the most intelligent animal in the farmyard - except perhaps for the farmer.

A more serious comparison

When a scientist suspects a plant or an animal is a hybrid he makes a long list of common features between the purported parents. McCarthy has done this between pigs and humans; all the features included are NOT shared with any other primate (other than the gorilla that might have a similar hybrid origin to humans).

McCarthy’s list has more than a hundred items, some are one liners, others detailed expositions of such as musculature, skeleton, organs and skin. NONE of these similarities are seriously disputed. Some scientists ponder why we share so much with a pig. They ignore the obvious explanation.

Most of these anatomical and external factors are too technical for my own understanding. For the sake of my argument I attempt to focus on just three

Skin. Including our mutual absence of hair our highly vascularised fatty skin is almost identical in structure and unlike that of any monkey. Our skin’s cooling capacity is outstanding. This is essential for cooling our very large brain. As an animal’s volume increases the problem of heat dispersal magnifies.

The intelligent small monkeys have a relatively small brain/body ratio. Not so the larger monkeys. There seems to be a barrier to large brains because the cooling requirement for a large brain is never achieved. If all our intelligence is to be housed in our small head we need a pig’s skin.

Bipedality. Although at first sight there seems to be no valid comparison there are in fact several pointers to a connection. A pig’s hind legs are longer than it’s forelegs. The pig’s and our own legs and hind skeleton and musculature is structured in such a way that bears little resemblance to that of a monkey. A monkey’s gait, even in those more highly developed with the capacity to walk on two legs show no sign of evolution to the way of our own.

It is conjecture whether the first pig/human hybrid came out two leg walking or developed it later!

Organs. I have no idea of the relative efficiencies of our organs to that of a monkey. Only that some of our organs are more like those of a pig than any monkey. Our kidney's intimate structure and action is the spitting image of that of a pig (perhaps relevant to our mutually omnivorous diet).

It does not follow that all structures in a new hybrid are at first or even ever especially beneficial. When huge numbers of genes recombine in a first hybrid it lives or dies with what it is endowed.

This does not imply that the offspring of new hybrids are not subject to later natural selection of new genes wherever they come from.

Envisaging the first pig/monkey hybrid

Even the most powerful new genetic techniques cannot inform us of what happened perhaps six million years ago at a time before than the appearance of the primate species that text books record as our likely ancestors. 

One can only surmise on our early hybrid origin based on our detailed knowledge of hybridisation and the introgression of genes in well researched modern examples.

Most people have an image of a modern farmyard pig mating with some humanoid creature. They immediately incredulously reject such a notion.

Wild pigs

Think more of two similar furry animals mating in the jungle or prairie (except that the swine might not have been hairy).

In their original habitats such liaisons might have been relatively common just as today mating is not infrequent between geographically overlapping genetically close  genera and species. (Most different species of monkeys can mate with each other if man brings them together)

What would be immensely rare would be such copulation giving rise to viable offspring. Recall however that if something is not impossible on an evolutionary timescale it is likely to happen. There are many parallels of genetically distinct animals that have given rise to viable and fertile hybrids.

Suppose a female monkey gives birth to a female hybrid. The hybrid’s likely fate is that it does not have the constitution to survive. There are however plenty of examples of distant hybrids that do reach maturity and behave as strange but functioning entities. Imprinted mother-love is fiercely powerful in ensuring such offspring’s survival.

If such an organism survived and in this case the monkeys were anything like modern promiscuous bonobos it would certainly mate!

Most hybrids are infertile but no means all. There are myriads of examples of plants and animals with different chromosome numbers crossing to produce fertile offspring.

Where a hybrid mates with one of the parent species it is called a backcross. Perhaps there were two backcross generations before the new form became physically or in some other way isolated to form a breeding community.

(I personally think there is too much pig in us for there to be many more backcrosses)

This kind of supposition does not preclude further liaisons between monkeys and the new species perhaps many generations later. Nor does it preclude introgression of some of the original sow’s genes into the offspring of the monkeys - but of course hugely diluted with thousands of generations of backcrossing and such genes only surviving if they gave strong selective advantage.

All this of course is speculation to how it might have happened. The actual pathway might have been completely different and most of the world denies it happened at all.

Final thoughts

I do not know how this theory will ever be proved. Perhaps more intensive genetic analysis of the similarities between humans and pigs might shed more light on the process. After all many of our shared features demand thousands of genes working in unison. Only if our skins for example achieved their similarities by entirely different gene pathways could the hybrid explanation be rejected.

No-one appears to be looking and you can easily understand why.

Readers might have previously noticed I am sceptical of the cavalier way that geneticists call upon parallel and diverging evolution to explain ‘difficult’ findings. Only yesterday researching this post I read that nature has reinvented the appendix in mammals 32 times! My own feeling is that the introgression of genes shared by hybridisation through chains of similar closely related species is a much more likely explanation of many such findings.

Mr McCarthy’s list of common features shared by pigs and humans and no other primates is extremely impressive and I discern that there is a vague recognition out there that this is an anomaly that seeks an explanation.

I really don’t know if the complex similarities between pigs and ourselves is controlled by arrays of very similar or identical genes. If it were to be so I cannot see any viable explanation exists for our common features other than a long past hybridisation. Classical methods of horizontal gene transfer in my view just don’t hold water as explanations of genetically distant animals (or plants) sharing complex features that are controlled by the same  genetic pathways.

The idea that there was a coastal phase in our early evolution perhaps 5 million years ago is no longer treated with derision. The theory is not entirely incompatible with the pig/monkey theory

A very recent article in the New Scientist positively gurgles over the importance of hybridity in human ancestry over the last 100,000 years. A professorial interviewee states that if you scratched wriggly overlapping lines on a piece of paper that would be our evolutionary pathway! How the story has changed in just a couple of years.

In contrast my article today speculates about a time a multiple of perhaps sixty times longer ago. It is quite ridiculous that with more recent acceptance that hybridisation is part of evolution (and not just an unfortunate artefact that arises from the dabbling of humans) that few seem to consider what hybridisation also occurred much-much longer ago.

Some readers might be interested in an article by Bryan Nelson on the MNN website about the recently discovered close genetic relationship between humans and pigs. He quotes the writer of the paper “ … swine could be placed in a family inhabited principally by primates….”

Reasons why the theory falls on stoney ground

1. Research in this area inspires ridicule and lacks funding. Just read this scurrilous and vindictive article in the Guardian - of all places

2. Successful experiments might in itself inspire ridicule, controversy and rejection

3. Failure to make research progress would destroy a career and label any researcher an idiot

4. Conventional opinion is only moving slowly to taking hybridisation seriously and many scientists’ life work is wedded to the belief that evolution only takes place in straight lines

5. Evolution is already rejected in the world’s hinterland. Don’t rock the boat by apparently changing your mind. Don’t give ammunition to ignorance

6. Should the theory ever be proven it would be a political hot potato

Further pigmentation

“Nothing in evolution would surprise me”  - Peter Williams

“They are our closest relatives”  - Michael Wood who has spent a lifetime working with pigs and temporarily overlooked monkeys

“This would be an unlikely coincidence”  -  Scientist commenting on the discovery that the Alu transposable RNA elements in pig and human are the same

“What we saw when living in the African jungle is not recorded in the text books”  - Cathi and Harry Poole

“Despite the great diversity of life, there is a string connecting us all together”  - Bryan Nelson

“My hatched duckling thought he was a hen and bonded with them - even ushered them into their pen at night”  - Cathi

Links
Bryan Nelson's perceptive MNN article

Scroll down on this page of Gene McCarthy's blog to find his list

My own most relevant hybridisation posts
1. About human evolution

2. Resistance to  hybridisation as an agent of evolution

What do you think?