In an earlier post I wondered more about the oddness of the evolution tree having fat branches but filament-thin trunk, likening it more to a fungus than a tree. In that post I also noted my plans to talk about some superficial similarities I see in humans and pigs while admitting my own fondness for pigs.
I pointed out a site I found that extensively documents an alternative theory of human evolution by Eugene M McCarthy. He had already did extensive research on the numerous similarities of humans and pigs. And he proposes a hybrid hypothesis that he backs up with his specialty in studying genetics of hybridization.
There are too many traits we share with pigs that are not shared with chimpanzees. There must have been a way to move a lot of pig information into the human genome. He proposes a hybridization solution that could work.
Although he is suggesting it could work in this case, it would be very rare and it just happened to work for creating hominids.
Another problem making it even unlikely is the large difference in mating behaviors in pigs and chimpanzees. It seems highly unlikely that a boar would be able to restrain a female chimpanzee for the duration it normally requires to have its way with her. The reverse seems more likely but sows are pretty picky about which offspring to nurture. It is unlikely to tolerate a malformed hybrid. Even if it were it is hard to imagine multiple generations of back-crossing with more pigs to get a human. Maybe it is possible that the fertilization was accidental contact by a female chimpanzee of fresh spilled boar semen.
I don’t dismiss the concept. It only has to work once.
Even if it were possible but highly unlikely and just happened to work for humans, it should raise some suspicion that somehow humans are special in a way most other species are not. We may even be unique.
I was playing in my mind a realization of the earliest hominids that they are not like the other animals who evolved normally, that they would kicked out of the chimpanzee tribe once the hominids back-crossed enough time to produce fertile males. I can imagine such hominids to have some kind of grudge against the rest of the natural world that turned into a sense of entitlement to rule over them all. They would have conceived of a creator god to explain why they were so special.
That silliness aside, I would prefer an explanation that wouldn’t make us so unique.
As he presents in other parts of his site, the fossil record supports a stabilization theory of evolution where new forms appear abruptly and then persist virtually unchanged until they become extinct. This occurs all the time. Hybridization could not explain all of these emergent species. Hybridization can’t even explain a few of them. It may have happened just once with the humans happening to get very lucky.
I would be curious if studies as he documents (comparing chimpanzees, humans, and pigs) have been performed on other species. I suspect there are many other cases showing similar patterns where the new form shares the majority of features with an earlier similar looking species but a few key distinguishing features from a more remote species not present in the first species.
I discussed my own pet theory that a virus could carry some host DNA with its own and make that DNA available to the new host. It was so weak that I readily admitted the hybridization model made more sense. The virus would have to be able to infect both species and the host DNA would need to be continuously carried through successive generations of viruses within the newly infected individual until it reached the reproductive system.
I’m sure such a proposal would be laughed out of freshman genetics class.
But then I wondered about the possibly unique vulnerability of the freshly fertilized egg still in a single cell stage. It is a fully functioning cell and starting life independent of the mother’s defenses. Could this cell be vulnerable to a virus that otherwise would not threaten a more mature individual?
A virus that normally can’t infect a particular species may have a partial success at infecting a freshly fertilized egg that lacks the defenses available to a more mature individual. Also, since the fertilized egg would still be a single cell, that cell would have immediate access to whatever piggyback DNA happened to be carried by the virus. There may be still enough incompatibility that the virus itself is not able to complete its life cycle so the cell is not killed. Instead the cell incorporates the DNA as part of its own and perhaps over the next few divisions selectively prunes out the the obnoxious virulent parts but inherits the more familiar DNA of the more distant relative.
The fertilized egg gets fertilized twice: by the sperm and by the virus that normally infects a completely different species. The individual effectively has three parents.
This is not a hybridization. The resulting individual is not weakened by the infection. The process could result in a viable and fertile offspring that could thrive to produce future generations with an additional new toolkit of genetic material to work with.
If a single-cell fertilized egg is more vulnerable to a virus infection by an incompatible virus that can’t reproduce in the egg but can transport some DNA from a different host, then this mechanism can occur through the entire animal and plant kingdoms. The events would be rare and random. New forms would occur at any time, not necessarily during stressful times.
As the referenced site documents, the stabilization theory suggests that a new form adapts the environment to its needs. Once it appears, it finds or builds its own niche possibly without edging out its predecessors at all. This process can occur contrary to the gradual change theory of evolution where the present population all have at least some differences from their predecessors. In this model, the unchanged predecessor and the new species could coexist. This coexistence may be common occurrence rather than unusual.
The exact event that branched the hominids from the chimpanzees is forever lost to history. It is unlikely that we’ll find that exact event. There is suggestive evidence that humans share a lot of traits with pigs. Any suggestion of how it got there is a hypothesis that may not be feasible to test. The actual event of the split is what I call dark data. We are certain that at some point the hominids must have had its own Adam and Eve. But we can only guess how they came to be. The hybrid hypothesis discussed in the referenced site is backed up with a lot of good research and knowledgeable expertise.
I claim the hypothesis that the individual had two parents is also an unproven hypothesis. That individual may have had zero parents as the result of some supernatural creation event. Or that individual may had more than two parents.
I find it exciting to think that genetic information can leap across the evolutionary tree. It suggests that we could experience an introduction of a new species at any moment instead of waiting for millions of years.
On the other hand we should not be surprised at the more than 2 parent hypothesis. Humans have already become proficient at genetic modification in a laboratory. Humans are just another part of nature, so this kind of modification has at least one natural explanation (get humans involved). But also, we keep finding natural examples of other beings performing tricks that we previously considered as uniquely human innovations. We find such examples even among insects (for example, ants as competent farmers). It not should surprise us if we find that nature has its own tricks for genetic transfer between distant species with much the same consequences as we achieve in our labs.
Addendum: As for the virus, I was thinking of thinking of the recent phenomena described as swine flu that can jump from pigs to humans. Perhaps at some point, a group of chimpanzees shared the same environment as a group of pigs suffering from some viral infection. The virus would be in the air but it would not be able to afflict the more mature chimpanzee. For whatever reasons that makes the chimpanzee immune to this virus, that immunity may be just slightly diminished in the gametes or the zygote just enough to allow the genetic material to be inserted but not enough to finish the viral cycle. The genetic material would intermingle at a time when the zygote is organizing itself. Perhaps this can occur repeatedly over many generations where the group of chimpanzees remains small and may at different times encounter a variety of swine populations that on occasion come down with a similar flu that provides some more information.
My hypothesis would also suggest perhaps the information was not limited to just one species of pigs or even just pigs. The forest is a busy place with a lot of populations that are subject to species-specific viral illnesses.