[Graeme]

A chimp-pig hybrid origin for humans?

Dr. Eugene McCarthy is a Ph.D. geneticist who has made a career out of studying hybridization in animals. He now curates a biological information website called Macroevolution.net where he has amassed an impressive body of evidence suggesting that human origins can be best explained by hybridization between pigs and chimpanzees. Extraordinary theories require extraordinary evidence and McCarthy does not disappoint. Rather than relying on genetic sequence comparisons, he instead offers extensive anatomical comparisons, each of which may be individually assailable, but startling when taken together. Why weren't these conclusions arrived at much sooner? McCarthy suggests it is because of an over-dependence on genetic data among biologists. He argues that humans are probably the result of multiple generations of backcrossing to chimpanzees, which in nucleotide sequence data comparisons would effectively mask any contribution from pig.

phys.org

[lper100km]

Apart from its improbability, there must be billions who find this idea somewhat offensive. Though maybe it is supported by the fact that porcine valve tissue is often used in heart valve surgery.

[PrestonSturges]

There have been emergency liver assist surgeries where the patients blood is shunted to a fresh pigs liver for a few hours.

Fast forward 20 years and we're working on cloning pig organs for humans, but those pigs will still have certain viruses, and they want to make sure that we won't create a new pig/human AIDS virus.

So researchers went back and checked the patients who years earlier had these temporary pig liver shunts to see if they had any pig viruses. They discovered that during these transfusions the patients had acquired live pig liver cells, and these cells were still in their bodies.

[Keith_McClary]

Apart from its improbability, there must be billions who find this idea somewhat offensive. Though maybe it is supported by the fact that porcine valve tissue is often used in heart valve surgery.

He mentions that.

He has many pages of arguments supporting his hypothesis.
http://www.macroevolution.net/hybrid-hy ... dT2iI7LIvQ
"I must admit that I initially felt a certain amount of repugnance at the idea of being a hybrid. The image of a pig mating with an ape is not a pretty one"
"the initial hybridization was between a boar and a female chimpanzee (which, for reasons soon to be stated, seems the likelier possibility)"

[KingM]

Please tell me you guys are not serious.

[Tanada]

A very silly theory IMO, Pigs only have 38 Chromosomes, Chimpanzees have 48 and Humans have 46. When animals with unequal numbers are crossed the resultant offspring if it even survives until birth is almost always sterile, like the crosses between Zebra's and Horses or Horses and Donkeys. Even very closely related populations of the same species that have been isolated for many generations have problems with sterile offspring, for example cattle and Yak. The first two generation of crossing the male offspring are all sterile despite the fact that both populations still have 60 Chromosomes and are only adapted for different weather climate environments.

We even know from gene mapping that Humans have 46 because two of our chromosomes became fused compared to those of Chimpanzee, Gorilla, Orang-u-tan who all have 48.

As for the tissue compatibility issue, compatibility is strictly a matter of does the incoming tissue have chemical receptors on it that trigger the bodies immune response system. If the answer is no then there won't be an immune response. That is why you can get blood from other people who share your blood type. It is also why siblings or identical twins are the best source of organs for anyone who needs a transplant, they have the best chance of not triggering an immune response. By the same token Human from Chimpanzee transplants and even Human from Baboon transplants have been preformed decades ago, but the populations of Chimpanzees and Baboons is tiny compared to the populations of farm animals. Pig organs are the farm animals closes in size to Humans so a lot of research was done to see if their parts could be used. The lucky circumstance that Pig heart valves often do not trigger an immune response has been good news for many patients, but it is not 100% the case, some patients still get sick and die from complications due to immune response.

So to sum up, only very closely related animals have offspring that survive, hooves and fingers don't match=fatal flaw=death in utero. Animals with the same body structure but different Chromosome counts have offspring that survive but that are Sterile, Donkey+Horse=Mule. Animals that have the same body structure and identical chromosome counts descended from the same ancestor can be fully fertile but are often partially sterile= Haldane Rule=Yak plus Cattle= fertile female offspring but sterile male offspring. Take any members of opposite genders of any species like two Chimpanzee from anywhere and they will have fertile offspring. Same goes for pigs. Cross a pig and a chimpanzee=dead fetus in utero due to body form incompatibility and chromosome count incompatibility.

[SeaGypsy]

The professor at work?

[Rune]

Well, whether or not there is any merit to McCarthy's ideas, there is certainly a lot of good reading, history, philosophy and evolution science, on his macroevolution.net website.

[Graeme]

Keith McClary gave a link to a website by the author, Dr Eugene McCarthy, who is very serious about this hypothesis. Before you dismiss it, please read all pages at this link including links to following sections.

So why do I think humans are hybrids? Well, first of all, I've had a different experience from most other people. I've spent most of my life (the last thirty years) studying hybrids, particularly avian and mammalian hybrids. I've read thousands, really tens of thousands, of reports describing them. And this experience has dispelled some mistaken ideas I once had about hybrids, notions that I notice many other people continue to take for granted.

For example, one widespread, but erroneous belief that keeps a lot of people from even considering the possibility that humans might be of hybrid origin is the notion that all hybrids are sterile. This assertion, though I've heard lots of people say it, is absolutely false. For instance, in reviewing the reports I collected for my book on hybridization in birds (Handbook of Avian Hybrids of the World, Oxford University Press, 2006), which documents some 5,000 different kinds of hybrid crosses among birds, I found that those producing partially fertile hybrids are about eight times as common as crosses known to produce sterile ones. So the usual result is a reduction in fertility, not absolute sterility. My current work documenting hybridization among mammals shows that partially fertile natural hybrids are common, too, in Class Mammalia. And yet, it seems most people base their ideas of hybrids on the common mule (horse x ass), which is an exceptionally sterile hybrid, and not at all representative of hybrids as a whole.

A second "fact" that might make it seem impossible for humans to have had a hybrid origin is the equally erroneous notion that hybrids, especially successful hybrids, do not occur in a state of nature. A third is the mistaken idea that only plants hybridize and never animals. In fact, however, natural, viable, fertile animal hybrids are abundant. A wide variety of such hybrids occur on an ongoing basis (read a detailed discussion documenting these facts). For example, of the 5,000 different types of hybrid crosses listed in my book on hybridization in birds, approximately half are known to occur in a natural setting (download a PowerPoint presentation summarizing data on hybridization in birds). My current research indicates a comparable rate for mammals.

On page 2, he lists the following traits which distinguish humans from other primates. He describes most the these in more detail in his article.

A list of traits distinguishing humans from other primates
DERMAL FEATURES
Naked skin (sparse pelage)
Panniculus adiposus (layer of subcutaneous fat)
Panniculus carnosus only in face and neck
In "hairy skin" region:
- Thick epidermis
- Crisscrossing congenital lines on epidermis
- Patterned epidermal-dermal junction
Large content of elastic fiber in skin
Thermoregulatory sweating
Richly vascularized dermis
Normal host for the human flea (Pulex irritans)
Dermal melanocytes absent
Melanocytes present in matrix of hair follicle
Epidermal lipids contain triglycerides and free fatty acids

FACIAL FEATURES
Lightly pigmented eyes common
Protruding, cartilaginous mucous nose
Narrow eye opening
Short, thick upper lip
Philtrum/cleft lip
Glabrous mucous membrane bordering lips
Eyebrows
Heavy eyelashes
Earlobes

FEATURES RELATING TO BIPEDALITY
Short, dorsal spines on first six cervical vertebrae
Seventh cervical vertebrae:
- long dorsal spine
- transverse foramens
Fewer floating and more non-floating ribs
More lumbar vertebrae
Fewer sacral vertebrae
More coccygeal vertebrae (long "tail bone")
Centralized spine
Short pelvis relative to body length
Sides of pelvis turn forward
Sharp lumbo-sacral promontory
Massive gluteal muscles
Curved sacrum with short dorsal spines
Hind limbs longer than forelimbs
Femur:
- Condyles equal in size
- Knock-kneed
- Elliptical condyles
- Deep intercondylar notch at lower end of femur
- Deep patellar groove with high lateral lip
- Crescent-shaped lateral meniscus with two tibial insertions
Short malleolus medialis
Talus suited strictly for extension and flexion of the foot
Long calcaneus relative to foot (metatarsal) length
Short digits (relative to chimpanzee)
Terminal phalanges blunt (ungual tuberosities)
Narrow pelvic outlet

ORGANS
Diverticulum at cardiac end of stomach
Valves of Kerkring present in small intestines
Mesenteric arterial arcades
Multipyramidal kidneys
Heart auricles level
Tricuspid valve of heart
Laryngeal sacs absent
Vocal ligaments
Prostate encircles urethra
Bulbo-urethral glands present
Os penis (baculum) absent.
Hymen
Absence of periodic sexual swellings in female
Ischial callosities absent
Nipples low on chest
Bicornuate uterus (occasionally present in humans)
Labia majora

CRANIAL FEATURES
Brain lobes: frontal and temporal prominent
Thermoregulatory venous plexuses
Well-developed system of emissary veins
Enlarged nasal bones
Divergent eyes (interior of orbit visible from side)
Styloid process
Large occipital condyles
Primitive premolar
Large, blunt-cusped (bunodont) molars
Thick tooth enamel
Helical chewing

BEHAVIORAL/PHYSIOLOGICAL
Nocturnal activity
Particular about place of defecation
Good swimmer, no fear of water
Extended male copulation time
Female orgasm
Short menstrual cycle
Snuggling
Tears
Alcoholism
Terrestrialism (Non-arboreal)
Able to exploit a wide range of environments and foods

RARE OR ABSENT IN NONHUMAN PRIMATES:
Heart attack
Atherosclerosis
Cancer (melanoma)

Here are his "closing thoughts" with regard to genetics.

In mammals, chromosomes are paired and vary widely in number from one type of organism to another. Each human cell contains 23 pairs — 22 matched pairs (autosomes) and one mismatched pair (the X and Y chromosomes). Pairing is important during meiosis, the process that produces spermatozoa and eggs. Germ cells are produced by cell division. At the beginning of each such division, each chromosome unites with the other member of its pair, a configuration called a tetrad. With chromosomes linked in pairs, the machinery of the dividing cell will distribute one member of each such pair into each of the two "daughter cells" produced by the division. When a tetrad is formed, the two homologous chromosomes composing it actually exchange DNA in a process termed crossing-over. Meiosis is stable under ordinary circumstances when organisms having the same karyotype mate (MORE ABOUT KARYOTYPES). There is little or no tendency for the number of chromosomes to change from one generation to the next. Chromosomes are not subjected to forces that rip them apart, rearrange them, and reassort them. But the picture changes in hybrids, where chromosomes become highly volatile.

When mating occurs between organisms belonging to different chromosets (as is almost invariably the case with organisms treated as separate species), some or all of the chromosomes of the resulting hybrid will be either unpaired or inexactly paired. Chromosomes lacking a match do not join to form a tetrad. No cellular mechanism exists to deal with unpaired chromosomes, so they pass into daughter cells at random.1 In this case, different daughter cells end up with different chromosome complements. Partially matched chromosomes unite to form partial tetrads and exchange lengthy blocks of DNA so that large groups of genes are transposed to new chromosomes. The chromosomes are radically altered both with respect to their genetic content and their overall appearance. (MORE INFORMATION)



Concluding Remarks

It seems to me that the information thus far presented is consistent with the idea that both humans and the gorilla originated by hybridization. For humans, the case appears strong, because the hypothesis accounts for such a large number of observations. I consider the gorilla guilty by association, even though far less empirical data is available — both for this animal and, in particular, for one of its two posited parents. I reach this conclusion because 1) the case for human hybridity is persuasive, 2) humans and gorillas both exhibit a pattern of infertility that is otherwise unexplained, and 3) the modicum of genetic and morphological information available for this animal is consistent with the posited hypothesis.

The tentative scenario that I picture is that human beings came into being via hybridization between a pig, whose best modern representative is Sus scrofa, and an ape, best represented today by the pygmy chimpanzee, Pan paniscus. I assume, as a working hypothesis, that before this hybridization event a population of Pan paniscus-like chimpanzees was distributed throughout the range of the chimpanzee, not just south of the Congo-Zaire-Lualaba river barrier where such animals are found today, but also north, in those areas where only the common chimpanzee is now found. Judging from what is known of the African climate in prehistoric times, I think the range of this proto-chimpanzee would probably have extended farther north than it does today, particularly in the Nile Valley. It would seem that sometime during the Pliocene, or more probably the Pleistocene, Sus scrofa, entered the range of the chimpanzee, and at some point hybridization occurred.

Now, it could be that this hybridization occurred only once in very ancient times (perhaps 5,000,000 years ago), producing the earliest hominids (australopithecines), and that various early human types hybridized to produce subsequent human types. It may be also that that various hominid types each arose via a separate cross between pig and chimpanzee. One fairly plausible scenario is that a hybridization event just prior to the time that modern humans first appeared (estimates for this date range from 100,000 to 140,000 years ago), probably somewhere in the Nile Valley, followed by an indeterminate number of generations of backcrossing to the chimpanzee. During this time the hybrids would have improved in fertility, eventually breaking off from the chimpanzee population to breed strictly among themselves. During this backcrossing period many pig-derived DNA sequences would become more and more like those of chimpanzees. The resulting high level of similarity to chimpanzees, together with the fact that our primate physical traits predominate, would explain why we have invariably been grouped with primates, and would also account for the fact that a connection between pigs and human beings has always been overlooked.

It also seems likely that the common chimpanzee crossed with Hylochoerus meinertzhageni, the giant forest hog, to produce the gorilla. This event way well have happened very recently (in fact, it may still be happening); no fossil remains have been found for the gorilla. The chimpanzee population (Pan troglodytes), also, appears to have been affected by this backcrossing, with some genetic influence carried across from Hylochoerus. This influence seems to be reflected today in such distinctive traits of the common chimpanzee such as large body size, heavy jaws and canines, the occasional sagittal crest, and higher levels of genetic and morphological variability (as compared with the genetically isolated residual population of pygmy chimpanzees). Hybridization between chimpanzees and Sus scrofa may also have produced the increased variability and size of common chimpanzee populations (in comparison with pygmy chimpanzees). Thus, I look on the common chimpanzee, itself, as a kind of hybrid, but only in the sense that some degree of genetic leakage seems to have seeped through from the human and, especially, the gorilla populations. The human genetic influence seems to be minimal, because backcrossing probably stopped long ago, but in the case of the gorilla it may be more substantial — hybridization appears to continue even today.

I think the question of the gorilla's hybridity will take longer to resolve than the human case. An immediate, obvious, hindrance is the paucity of information available for the gorilla and, especially, for the forest hog. In addition, several factors seem to indicate that the gorilla may be more highly backbred to the chimpanzee: 1) Ongoing hybridization seems to be occurring in the case of the gorilla; 2) Gorilla and chimpanzee chromosome counts are identical (2n=48), while the human count is lower (2n=46); 3) Fewer morphological differences seem to exist between gorilla and chimpanzee than between chimpanzee and Homo sapiens.

I must admit that I initially felt a certain amount of repugnance at the idea of being a hybrid. The image of a pig mating with an ape is not a pretty one, nor is that of a horde of monstrous half-humans breeding in a hybrid swarm. But the way we came to be is not so important as the fact that we now exist. As every Machiavellian knows, good things can emerge from ugly processes, and I think the human race is a very good thing. Moreover, there is something to be said for the idea of having the pig as a relative. My opinion of this animal has much improved during the course of my research. Where once I thought of filth and greed, I now think of intelligence, affection, loyalty, and adaptability, with an added touch of joyous sensuality — qualities without which humans would not be human.

When it comes to topics like human origins, where the opinions are rigid and the evidence thin, reservation of judgment is best. It is my hope that the arguments presented here will serve as an intellectual springboard allowing the mind to rise above the inflexible creeds of traditional evolutionary thought. Even if the hybrid hypothesis is wrong, any satisfactory theory of human evolution will have to address the facts touched upon in the foregoing discussion. Wrong or right, I believe a final answer is at hand. The obstacles to the acquisition of such knowledge are by no means insurmountable. Scientists around the world are gathering more data every day. If this rising tide of information indicates that the ideas that we have always had about our origins are wrong, we should not hesitate to correct our errors. Time after time, science has dispelled dogma and brought us things that were once beyond imagination. From tiny bacteria to vast galaxies, from telephones to rocket ships, our knowledge has continued to expand. Perhaps we will even at last be able to rend the veil that has long obscured our own origins. If the hybrid hypothesis is correct, we will be able to find out where we came from. One simple thing is essential to that discovery: In the immortal words of Professor Bernhardt, "It isn't faith that makes good science, Mr. Klatu. It's curiosity!"

[Tanada]

Graeme, two points. First hybridization between birds is easy to accomplish for several reasons, for one they lay eggs so there is little chance the developing fetus would be rejected as it would be in Mammals because the egg is only fertilized before being ejected from the female body, internal gestation and possible rejection is not a factor. Secondly every animal we define as a bird has the same general body form, they all have feathers, they all have wings, even penguins. They all lay eggs and nest with those eggs for incubation. Also I clearly pointed out in my earlier post that fertility of hybrids is a factor of mainly two things, how closely they physically resemble one another and how closely they genetically resemble each other in chromosome count. Hybridizing birds with the same chromosome count from the same region with the same habitat is not a surprise, it is a perfectly normal expectation. It is argued that if the offspring are fertile then the hybrid is not a separate species.

Secondly all of the traits that he points to about humans being different from the other great apes is covered by the Aquatic Ape Theory http://www.primitivism.com/aquatic-ape.htm selected quotes below, please read the whole link for deeper understanding.

Humans are classed anatomically among the primates, the order of which includes apes, monkeys and lemurs. Among the hundreds of living primate species, only humans are naked.

Two kinds of habitat are known to give rise to naked mammals - a subterranean one or a wet one. There is a naked Somalian mole rat which never ventures above ground. All other non-human mammals which have lost all or most of their fur are either swimmers like whales and dolphins and walruses and manatees, or wallowers like hippopotamuses and pigs and tapirs. The rhinoceros and the elephant, though found on land since Africa became drier, bear traces of a more watery past and seize every opportunity of wallowing in mud or water.

One general conclusion seems undeniable from an overall survey of mammalian species: that while a coat of fur provides the best insulation for land mammals the best insulation in water is not fur, but a layer of fat.

Fat

Humans are by far the fattest primates; we have ten times as many fat cells in our bodies as would be expected in an animal of our size.

There are two kinds of animals which tend to acquire large deposits of fat - hibernating ones and aquatic ones. In hibernating mammals the fat is seasonal; in most aquatic ones, as in humans it is present all the year round. Also, in land mammals fat tends to be stored internally, especially around the kidneys and intestines; in aquatic mammals and in humans a higher proportion is deposited under the skin.

The other difference is that in our case the subcutaneous fat is bonded to the skin. When an anatomist skins a cat or rabbit or chimpanzee, any superficial fat deposits remain attached to the underlying tissues. In the case of humans, the fat comes away with the skin, just as it does in aquatic species like dolphins, seals, hippos and manatees.

Today, two primates when on the ground stand and walk erect somewhat more readily than most other species. One, the proboscis monkey, lives in the mangrove swamps of Borneo. The other is the bonobo or pygmy chimpanzee; its habitat includes a large tract of seasonally flooded forest, which would have covered an even more extensive area before the African climate became drier.

Both of these species enjoy the water. It is interesting that the bonobos often mate face-to-face as humans do; in our case it is explained as a consequence of bipedalism. This mode of mating is another characteristic very rare among land animals, which we share with a wide range of aquatic mammals such as dolphins, beavers and sea otters. What we have in common with them is a mode of locomotion in which the spine and the hind limbs are in a straight line, and that affects the position of the sex organs.

The human respiratory system is unlike any other land mammal's in two respects.

The first is that we have conscious control of our breathing. In most mammals these actions are involuntary, like the heart beat or the processes of digestion.

Voluntary breath control appears to be an aquatic adaptation because, apart from ourselves, it is found only in aquatic mammals like seals and dolphins. When they decide how deep they are going to dive, they can estimate how much air they need to inhale. Without voluntary breath control it is very unlikely that we could have learned to speak.
Other differences

It is impossible in a brief outline to discuss all the physical features distinguishing us from the apes, but a few are worth mentioning.

For example, we have a different way of sweating from other mammals, using different skin glands. It is very wasteful of the body's essential resources of water and salt. It is therefore unlikely that we acquired it on the savannah, where water and salt are both in short supply.

We weep tears of emotion, controlled by different nerves from the ones that cause our eyes to water in response to smoke or dust. No other land animal does this. There are marine birds, marine reptiles and marine mammals which shed water through their eyes, or through special nasal glands, when they have swallowed too much seawater. This process may also be triggered in them by an emotional excitement caused by feeding or fighting or frustration. Weeping animals, apart from ourselves, include the walrus, the seal and the sea otter.

We have millions of sebaceous glands which exude oil over head, face and torso, and in young adults often causes acne. The chimpanzee's sebaceous glands are described as "vestigial" whereas ours are described as "enormous". Their purpose is obscure. In other animals the only known function of sebum is that of waterproofing the skin or the fur.

AAT is the only theory which logically connects all these and other enigmatic features and relates them to a single well attested historical event.

By these criteria we are more closely related physiologically to the Elephant, Hippo, or Seal than we are to the Pig.

[SeaGypsy]

Remember the New Age spin on the Aquatic Ape?- The story was linked to how dolphin trainers first have to teach their students to stop trying to copulate- with the trainer. We are a dolphin-ape! (Where's VM)

[AdTheNad]

OK, I don't know that much about these things so there might be simple reasons to explain the doubts that I have, however:

Surely there would be some DNA evidence if we were a pig hybrid, even if it was difficult to find due to the backcrossing mentioned?

What about things like tracing mitochondrial DNA?

Could we make a chimpanzee pig hybrid now as proof of concept?

Seriously, this reminds me of the expanding earth hypothesis, as in anti scientific nonsense, sponsored either by the anti science brigade or just some fella looking to sell a book. I'm always open to changing my opinion if the evidence exists though.

[Keith_McClary]

fertility of hybrids is a factor of mainly two things, how closely they physically resemble one another and how closely they genetically resemble each other in chromosome count.

Did McCarthy address this - give any non-close mammalian examples? (I didn't re-read to check).

Hybridizing birds with the same chromosome count from the same region with the same habitat is not a surprise, it is a perfectly normal expectation.

My bird expert friend says this is common in ducks. He attributes it to their poor eyesight.

[Graeme]

Tanada, McCarthy has described in the link above the process for forming a partial tetrad and backcrossing:

Obviously, the germ cells produced by such mechanisms would vary widely in genetic content. Depending on the cross in question, a larger or a smaller proportion of these gametes, and the later-generation hybrids produced by them, would be inviable. The process of exchange, breakage, repair, loss, and reassortment would continue — in each gamete, in each individual, in every generation — as hybrids mated among themselves and/or with pure individuals of the parent types. The jumbling and reassortment of genomic components in such a population would repeat in every generation until all chromosomes were paired in every individual and meiosis became stable once again.

So the karyotype characterizing any such emergent, re-stabilized population would be unlike either of the karyotypes present in the parents that initially crossed. During the unstable period, chromosomes would have been broken up and reconnected in new configurations as well as reassorted into new karyotypes composed of chromosomes and genes previously present only in separate organisms. If a new type of organism — for example Homo sapiens — emerged from a chromosomal mishmash such as that just described, its chromosomes would differ in structure from those of either of its two parents. Repeated crossing-over, breakage, repair, and reassortment would have created chromosomes in which genes from both parents were mingled. And, as it happens, human chromosomes have in fact been extensively rearranged in comparison with those of chimpanzees, a fact that has never been satisfactorily explained in terms of conventional theory.

Recall that a backcross is a mating of a hybrid with one of the parental types that originally crossed to produce it. If hybrids backcross solely with only one of their two parental types, then that type contributes most of the DNA to the genome of the backcross offspring. If these offspring then backcross again, then their progeny will be even more similar genetically to the backcross parent. An even larger fraction of their DNA will be from the backcross parent. Moreover, as we have seen, even any DNA derived from the other, non-backcross parent becomes more and more like that of the backcross parent with each successive backcross due to the effects of gene conversion (if you need to refresh your memory on this point, please read the green sidebar at right, entitled "Why genetic data cannot be used to evaluate the hypothesis").

In the case of early "humans," if the initial hybridization was between a boar and a female chimpanzee (which, for reasons soon to be stated, seems the likelier possibility), the initial hybrid offspring would be born into a chimpanzee troop, which would increase the chances of the hybrid(s) backcrossing with chimpanzees. After an initial generation of backcrossing, the probability of additional backcrossing in later generations would be further increased because the backcross hybrids would be more chimpanzee-like and would again have grown up among chimpanzees. So they would be expected to have an even greater affinity for chimpanzees than did hybrids from the initial cross. And, as has I have already emphasized, a hybrid population repeatedly backcrosses to only one of its two parents, the DNA of that parent comes to predominate in the genomes of the hybrids. Long-term backcrossing over many generations can eliminate in the hybrids every genetic trace of the other parent. Of course, when the hybrid becomes genetically (genotypically) identical to one of its parents, it will also be indistinguishable in terms of its physical (phenotypic) traits.

Hybrids can maintain their existence as distinct entities only if at some point they can stop backcrossing and start mating among themselves. To do this, however, they would have to be more fertile than in the case of backcrossing. When two individuals of low fertility mate, the chances of producing progeny are much lower than when one such individual mates with a fully fertile parental-type individual. Moreover, in many crosses, hybrids will be of only one sex in the initial generation. In other crosses one sex among the hybrids is sterile. In either case, backcrossing becomes an absolute necessity. In some cases, the initial hybrids may be so rare that backcrossing is the only way to find a mate. At the same time, however, fertility tends to increase in hybrids with each generation of backcrossing. When fertile, or partially fertile, backcross hybrids of both sexes begin to appear, the hybrid population has the option of breaking off and forming its own isolated population. So long as they can produce in every generation a sufficient number of offspring to maintain the population, they can persist even though their fertility may remain poor for many generations thereafter.

In a pig-ape hybrid the chromosomes would be almost entirely unpaired. Meiosis would therefore be severely disrupted. There would be erratic segregation of the chromosomes into gametes, as well as extensive breakage, restructuring, loss, and reassortment of chromosomes — mass mutation. Genetic content would vary widely from one gamete to another. Under such circumstances, many gametes would not even have the genetic wherewithal to reach functional maturity (hybrids, especially ones derived from distant crosses, typically produce far fewer functional gametes than do nonhybrid individuals of normal fertility). Moreover, among those few gametes that did mature, even fewer would develop into mature organisms capable of producing offspring.

So even if a rare pig-ape hybrid was actually able to find a mate of its own kind, such a pairing would be highly unlikely to produce viable offspring because, a mating between two individuals of low fertility has a small chance of success. The chances would be greater, if the initial hybrid backcrossed. And this supposition is consistent with observation since in a wide variety of crosses second generation hybrids are produced only in backcrosses, and not by matings among the F₁ hybrids.

In the case of a pig-ape hybrid backcrossing would most likely have been with chimpanzees because the mother in the initial cross would, almost surely have been a chimpanzee. There are at least three reasons to reach this conclusion. The first is that a chimpanzee penis would probably be incapable of impregnating a sow, but a boar's penis would be fully capable of carrying out the insemination process with sex roles reversed.2 The second is that a humanlike hybrid would likely require a long period of nurture that a sow would not be able to provide. The third is that during estrus a pink sexual swelling appears on the rump of the female chimpanzee. Chimpanzee males do not attempt to engage in coitus, even with females of their own kind, unless this swelling is present.3 A boar, on the other hand, will mount any immobile object capable of supporting him, and will voluntarily ejaculate even into an inanimate tubular receptacle if it is of suitable diameter. "It does appear then as if, as far as the boar is concerned, coitus is largely a mechanical process" (Rodolfo4). When threatened, chimpanzee females often attempt to appease the aggressor by crouching down and presenting their genitals.

Thus, if an initial (F₁) hybrid was ever produced from this cross, its mother would almost certainly have been a chimpanzee — particularly given that a humanlike hybrid infant would require a mother that could hold it and nurture it for a prolonged period of time. The hybrid would therefore have grown up in a chimpanzee troop and, upon reaching sexual maturity, would have been in everyday contact with chimpanzees and would have thought of chimpanzees as its own kind. Many animals imprint on the animal that raises them and later prefer sex with animals of that type. The same might have been true of proto-humans raised by chimpanzees. I say "proto-humans" because any progeny of an initial cross between pigs and chimpanzees would have nearly half of their DNA from pigs and would thus be much more similar to pigs than are modern humans (the pig genome is about 10% smaller than that of a chimpanzee, so even in the F₁ hybrid chimpanzee DNA would slightly preponderate). Only with successive generations of backcrossing would these piglike traits be reduced, as the backcross hybrids became genetically more similar to chimpanzees. An additional reason, then, to suppose that Homo sapiens is the result of backcrossing to chimpanzees is the observed preponderance of primate characteristics in humans.

The series of matings producing humans could perhaps have been completed in only a few generations, but could also have taken many, and have involved a complex mixture of backcrosses and matings of hybrid with hybrid. At this distance in time it's probably impossible to reconstruct the exact series of events. However, for the reasons just stated, it does seem clear that extensive backcrossing to chimpanzees must have occurred. And yet, despite the homogenization of nucleotide sequences resulting from that backcrossing, the hybrids would not become physically indistinguishable from the backcross parent as quickly as their nucleotide sequences did. Under the hybrid hypothesis, this fact that humans have remained physically quite distinct from chimpanzees despite their extreme similarity in terms of protein and nucleotide sequences, can be easily explained.

He is proposing a new theory for the origins of life. As an expert on hydribrization, he doesn't buy the "aquatic" theory (see page 245: primates are not aquatic animals).

[SeaGypsy]

Aquatic ape makes a lot more sense than this mumbo jumbo. Humans have been diving for food for much longer than farming.

[Graeme]

According to McCarthy, primates are notorious for their inability to swim.

[Tanada]

According to McCarthy, primates are notorious for their inability to swim.

That is a false statement, Chimpanzees, Gorilla's and Orag-U-Tans are noted for their lack of swimming ability while several other primates and many monkeys swim just fine thank you very much. Even so all known Primates will cross water up to chest deep by wading and there are examples of others foraging for food in the shallows. There is even a tribe of monkey's in Japan that swims and dives for rice thrown in the warm springs to attract them for tourists.

[SeaGypsy]

Among the most ancient marks of human evolution; the middens built over millenia of shellfish hunts caught in often dangerous and deep waters with nothing more than a sharp rock and a string bag.

[Graeme]

Here are some more thoughts of mine. There is no question that McCarthy is an expert on hydrids. He's very well qualified with a PhD. There is also no question that his theory is controversial because of the objections raised here and the fact that it is not published in any scientific journal. McCarthy is putting his entire reputation and career at risk by publishing his theory in the only other media outlet that is now available to him, namely the Internet. He is exercising his freedom of speech in a country where it is permitted. Fortunately, this site also allows his controversial theory to be scrutinized and criticized. That is to be applauded. Whether he is a modern day American Darwin, who needs a Huxley, or a fool remains to be seen. I don't think the comments so far have ruled his theory out. I haven't seen any other comments about his theory by other professionals. Until it is thoroughly tested and examined by his peers, he should be given the benefit of doubt. In his final comments above, he mentions that the case for chimpanzee-pig hydrids is "strong" but the case for other primate-pig hydrids to make gorilla is "weaker". Even he expresses some doubt.

It is my hope that the arguments presented here will serve as an intellectual springboard allowing the mind to rise above the inflexible creeds of traditional evolutionary thought. Even if the hybrid hypothesis is wrong, any satisfactory theory of human evolution will have to address the facts touched upon in the foregoing discussion. Wrong or right, I believe a final answer is at hand.

[Graeme]

There has been some recent research into the genetic history of 79 of the great apes including humans published in July Issue of Nature, and reported by Livescience.

Surprisingly, Marques-Bonet said, the genetic history of chimpanzees turned out to be much more complex than that of humans. Compared with chimps, "it looks like our [humans'] history has been really simple," Marques-Bonet said. Human populations encountered a bottleneck when they left Africa, and have since expanded to colonize the whole planet. By contrast, chimpanzee populations have undergone at least two to three bottlenecks and expansions, Marques-Bonet said.

The findings, the researchers said, also settle a hot debate over the relationships among the four chimpanzee subspecies — Central chimpanzee, Western chimpanzee, Nigeria-Cameroon chimpanzee and Eastern chimpanzee. "Now, we have the full genome for all four," Marques-Bonet said. Rather than revealing four groups, the sequences show that all chimps divide into two major groups: a Nigeria-Cameroon/Western population and a Central/Eastern population.

The new findings don't change humans' position in the great-ape evolutionary tree. Chimpanzees and bonobos are still humans' closest living relatives, splitting off from humanity about 5 million years ago. Humans' next-closest living relatives are gorillas, and orangutans are the most distantly related of the great apes.

Despite the genetic similarity between humans and chimpanzees, the two species are clearly quite different. Some scientists had hypothesized that the differences stem from the "lost" parts of human genomes compared with chimp genomes. But the new study disproved that theory by showing that the lost parts were mostly nonfunctional.

So if it's not genetics, what makes humans different from their great-ape cousins? "If I knew, I would have the Nobel Prize," Marques-Bonet said.