Pharyngula

I know you’re thinking we’ve had more than enough discussion of one simplistic umbrella hypothesis for the origin of unique human traits — the aquatic ape hypothesis — and it’s cruel of me to introduce another, but who knows, maybe the proponents of each will collide and mutually annihilate each other, and then we’ll all be happy. Besides, this new idea is hilarious. I’m calling it the MFAP hypothesis of human origins, which the original author probably wouldn’t care for (for reasons that will become clear in a moment), but I think it’s very accurate.

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)

First, the author of this new hypothesis provides a convenient list of all the unique traits that distinguish humans from other primates, listed on the right. It falsely lists a number of traits that are completely non-unique (such as female orgasm and cancer), or are bizarre and irrelevant (“snuggling”, really?). It’s clearly a selective and distorted list made by someone with an agenda, so even though some items on the list are actually unusual traits, the list itself is a very poor bit of data.

But set those objections to the list aside for a moment, and let’s consider the hypothesis proposed to explain their existence, the MFAP Hypothesis of Eugene McCarthy, geneticist. I will allow him to speak for himself at length; basically, though, he proposes that the way novel traits appear in evolution is by hybridization, by crosses between two different species to produce a third with unique properties.

Many characteristics that clearly distinguish humans from chimps have been noted by various authorities over the years. The task of preliminarily identifying a likely pair of parents, then, is straightforward: Make a list of all such characteristics and then see if it describes a particular animal. One fact, however, suggests the need for an open mind: as it turns out, many features that distinguish humans from chimpanzees also distinguish them from all other primates. Features found in human beings, but not in other primates, cannot be accounted for by hybridization of a primate with some other primate. If hybridization is to explain such features, the cross will have to be between a chimpanzee and a nonprimate — an unusual, distant cross to create an unusual creature.

For the present, I ask the reader to reserve judgment concerning the plausibility of such a cross. I’m an expert on hybrids and I can assure you that our understanding of hybridization at the molecular level is still far too vague to rule out the idea of a chimpanzee crossing with a nonprimate. Anyone who speaks with certainty on this point speaks from prejudice, not knowledge.

Let’s begin, then, by considering the list in the sidebar at right, which is a condensed list of traits distinguishing humans from chimpanzees — and all other nonhuman primates. Take the time to read this list and to consider what creature — of any kind — it might describe. Most of the items listed are of such an obscure nature that the reader might be hard pressed to say what animal might have them (only a specialist would be familiar with many of the terms listed, but all the necessary jargon will be defined and explained). For example, consider multipyramidal kidneys. It’s a fact that humans have this trait, and that chimpanzees and other primates do not, but the average person on the street would probably have no idea what animals do have this feature.

Looking at a subset of the listed traits, however, it’s clear that the other parent in this hypothetical cross that produced the first human would be an intelligent animal with a protrusive, cartilaginous nose, a thick layer of subcutaneous fat, short digits, and a naked skin. It would be terrestrial, not arboreal, and adaptable to a wide range of foods and environments. These traits may bring a particular creature to mind. In fact, a particular nonprimate does have, not only each of the few traits just mentioned, but every one of the many traits listed in th sidebar. Ask yourself: Is it is likely that an animal unrelated to humans would possess so many of the “human” characteristics that distinguish us from primates? That is, could it be a mere coincidence? It’s only my opinion, but I don’t think so.

Look at the description of the putative non-primate parent in the last paragraph above. What animal are you thinking of? It’s probably the same one McCarthy imagined, which is why I’ve decided that this explanation for human origins must be called the Monkey-Fucked-A-Pig hypothesis, or MFAP for short.

Let’s be perfectly clear about this. McCarthy’s hypothesis is that once upon a time, these two met and had sex,

angrypigangrychimp

And that they then had children that were…us.

That’ll learn me. I thought this South Park clip was a joke.

One thing that struck me in reading McCarthy’s claim is how they are so similar to the claims of the soggy ape fans — they even use the very same physiological and anatomical features to argue for their delusion. For instance, I’ve read aquatic ape proponents’ arguments that the shape of our nose is adaptive for streamlining and for preventing water from flowing into the nostrils while propelling ourselves forward through the water…but compare that to the MFAP.

Neither is it clear how a protrusive cartilaginous nose might have aided early humans in their “savannah hunter lifestyle.” As Morris remarks, “It is interesting to note that the protuberant, fleshy nose of our species is another unique feature that the anatomists cannot explain.” This feature is neither characteristic of apes, nor even of other catarrhines. Obviously, pigs have a nose even more protuberant than our own. In a pig’s snout, the nasal wings and septum are cartilaginous as ours are. In contrast, a chimpanzee’s nose “is small, flat, and has no lateral cartilages”. A cartilaginous nose is apparently a rare trait in mammals. Primatologist Jeffrey Schwartz goes so far as to say that “it is the enlarged nasal wing cartilage that makes the human nose what it is, and which distinguishes humans from all other animals.” The cartilaginous structure of the pig’s snout is generally considered to be an “adaptation” for digging with the nose (rooting). Rooting is, apparently, a behavior pattern peculiar to pigs. Other animals dig with their feet.

Point, MFAP. Of course, just as I would point out to aquatic ape people, we do have an explanation for the nose: recession of the facial bones associated with reduced dentition, along with retention of the bones associated with the respiratory apparatus. The protuberant nose is simply a ridge made apparent by the receding tide of our chewing apparatus. McCarthy uses evidence as badly as does every wet ape fan.

Now, why won’t this hybridization claim work? Well, there are the obvious behavioral difficulties, even if it were cytogenetically possible. We’d have to have pigs and chimps having sex and producing fertile offspring, and those human babies (remember, this is a saltational theory, so the progeny would have all the attributes of a third species, ours) would have to be raised by chimps. Or pigs. I don’t think either is a reasonable alternative, and a band of chimps would probably be no more charitable to a helpless fat blob of a baby than Mr Wu’s pigs.

However, no one reasonably expects pigs and chimps to be interfertile. The primate and artiodactyl lineages have diverged for roughly 80 million years — just the gradual accumulation of molecular differences in sperm and egg recognition proteins would mean that pig sperm wouldn’t recognize a chimpanzee egg as a reasonable target for fusion. Heck, even two humans will have these sorts of mating incompatibilities. Two species that haven’t had any intermingling populations since the Cretaceous? No way.

pig-chimp_lca

But further, even if the sperm of one would fuse with the egg of another, there is another looming problem: chromosome incompatibilities. Pigs have 38 chromosomes, chimpanzees have 48. Cells are remarkably good at coping with variations in chromosome number, and even with translocations of regions from one chromosome to another; and further, pigs and people even retain similar genetic arrangements on some of their chromosomes. There are pig chromosomes that have almost the same arrangement of genes as a corresponding human chromosome.

But there are limits to how much variation the cell division machinery can cope with. For instance, with fewer chromosomes than we primates have, that means you need to line up multiple primate chromosomes to match a single pig chromosome (this pairing up is essential for both mitosis and meiosis). Look at pig chromosome 7, for instance: it corresponds to scrambled and reassembled bits of human chromosomes 6, 14, and 15.

Blocks of conserved synteny between pig and human. (a) Pig SSC7 to human chromosomes 6, 14 and 15. (b) HSA13 compared to pig chromosome 11. Block inversions between pig and human are denoted with broken lines. Contig coverage is depicted by bars in the center of SSC7 and HSA13.

Blocks of conserved synteny between pig and human. (a) Pig SSC7 to human chromosomes 6, 14 and 15. (b) HSA13 compared to pig chromosome 11. Block inversions between pig and human are denoted with broken lines. Contig coverage is depicted by bars in the center of SSC7 and HSA13.

Maybe that would work in mitosis within the hybrid progeny — you’d have three chromosomes from the human/chimp parent twisted around one chromosome, but they would be able to pair up, mostly, and then separate to form two daughter cells. But meiosis would be total chaos: any crossing over would lead to deletions and duplications, acentric and dicentric chromosomes, a jumble of broken chromosomes. That would represent sterile progeny and an evolutionary dead end.

But we wouldn’t have to even get that far. Human and chimpanzee chromosomes are even more similar to one another, and there are no obvious chromosomal barriers to interfertility between one another. If hybridization in mammals were so easy that a pig and a chimp could do it, human-chimp hybrids ought to be trivial. Despite rumors of some experiments that attempted to test that, though, there have been no human-chimp hybrids observed, and I think they are highly unlikely to be possible. In this case, it’s a developmental problem.

For example, we have bigger brains than chimpanzees do. This is not a change that was effected with a single switch; multiple genes had to co-evolve together, ratcheting up the size in relatively incremental steps. So you could imagine a change that increased mitotic activity in neural precursors that would increase the number of neurons, but then you’d also need changes in how those cells are partitioned into different regions, and changes in the proliferation of cartilage and bone to generate a larger cranium, and greater investment in vascular tissue to provide that brain with an adequate blood supply.

Development is like a ballet, in which multiple players have to be in the right place and with the right timing for everything to come off smoothly. If someone is out of place by a few feet or premature by a few seconds in a leap, the dancers could probably compensate because there are understood rules for the general interactions…but it would probably come off as rough and poorly executed. A hybrid between two closely related species would be like mixing and matching the dancers from two different troupes to dance similar versions of Swan Lake — everything would be a bit off, but they could probably compensate and muddle through the performance.

Hybridizing a pig and a chimp is like taking half the dancers from a performance of Swan Lake and the other half from a performance of Giselle and throwing them together on stage to assemble something. It’s going to be a catastrophe.

But here’s the deal: maybe I’m completely wrong. This is an experiment that is easily and relatively cheaply done. Human sperm is easily obtained (McCarthy probably has a plentiful supply in his pants), while artificial insemination of swine is routine. Perhaps McCarthy can report back when he has actually done the work.


Humphray SJ, Scott CE, Clark R, Marron B, Bender C, Camm N, Davis J, Jenks A, Noon A, Patel M, Sehra H, Yang F, Rogatcheva MB, Milan D, Chardon P, Rohrer G, Nonneman D, de Jong P, Meyers SN, Archibald A, Beever JE, Schook LB, Rogers J. (2007) A high utility integrated map of the pig genome. Genome Biol. 8(7):R139.

Comments

  1. #1 Graham
    July 2, 2013

    It would be nice if AAH and MFAP annihilated one another, but I fear a hybrid theory involving dolphins.

  2. #2 rork
    July 2, 2013

    If one was really interested in testing the hypothesis, I think looking at DNA, rather than earlobe or coccyx, would be the modern method of attack. Folks who want first settlers of the americas to be other than the Amerinds we actually observe are also very careful to never mention the lack of DNA evidence.
    I am there doubtful that McCarthy has a genetics PhD, or if he does, perhaps he is just having fun – showing us how people in the old days could make bullshit theories up, since the DNA couldn’t contradict them.

  3. #3 lightning
    July 3, 2013

    WTF?? Is this guy a troll or just a head case? Is he worth any more mental effort than the Timecube guy?

    I know you probably didn’t intend this, but it makes the Aquatic Ape hypothesis sound downright sensible.

  4. #4 Trottelreiner
    July 3, 2013

    err, when i first read the list, my thoughts were more with, well…

    loxodonta

    makes for funny pictures, and we could even cite cultural signs of this, with the buddha conceived as an white elephant and thus. so may i propose the mfae- or dilf-theory[1] of human origins?

    as for the human-chimp hybrids, iirc there are indications of some gene flow even after the initial split of homo and pan, for actual hybrids, in a discussion of err, “baraminology”, one biologist mentioned early embryonic stages of these are known. actually that was more with homo and pan thus being part of one baramin and “baraminologists” being somewhat quiet about this, which might have something to do with the whole concept of “baraminology” being an idea of creationists. no citatins, though.

    btw, could somebody please give me the trepanator and the bleach, now? especially with the drawing ofone guy i onew of the conceptioj of the buddha, err?

    [1] dumbo i like to fuck; come to thin about it, i always thought protruding ears kinda cute in girls, err.

  5. #5 Jim Thomerson
    July 3, 2013

    Interspecific hybrids generally exhibit a suite ofcharacteristics; some of which are intermediate between the parent species, like one parent or the other, or unlike either parent. Just saying.

    I have been mulling over the “throwing ape” hypothesis. Our ancestors had a toolkit which allowed them to become ancestors. It looks like some of our early relatives were relatively small and weak, and had unimpressive teeth. Compared to a modern human, some of whom make big bucks throwing hard and accurately, a chimp, in spite of its much greater arm strength, can throw at 12 mph max.

    Throwing hard and accurately allows one to effectively engage prey or predators at a much safer distance. It also gets one into thinking about which rocks are best to throw, and intuitive physics. So I propose that the major evolutionary advancement of the Homo lineage was the ability to throw. I suppose, as an ichthyologist (what do I know about human evolution), I should support the aquatic ape hypothesis. ;-)

  6. #6 David
    July 4, 2013

    It’s interesting to note that Skin Wrinkling of wet fingers occurs via autonomic nerve signalling that causes vasoconstriction not osmotic absorption of water And wrinkled skin improves grip in wet conditions, akin to a wet weather tire tread. It was observed in the 1930s that severed finger nerves stops wet fingers from wrinkling.

    Does anyone know if the skin on a Chimpanzee’s fingers wrinkle when wet?

    Kareklas, K., Nettle, D., and Smulders, T.V., 2013, Water-induced finger wrinkles improve handling of wet objects: Biology Letters, v. 9, no. 2, doi: 10.1098/rsbl.2012.0999.

  7. #7 John
    NJ
    July 4, 2013

    I had just read the MFAP theory elsewhere and thought it sounded ridiculous. I know there are plenty of animal hybrids that have occurred, but they were between species that were obviously related (lions+tigers, horses+zebras, dogs+wolves, etc). A pig+chimp pairing seemed too distant to be credible, but I figured I’d swing by here and see if there was anything on this.

  8. #8 Ruth
    Australia
    July 5, 2013

    “Hybridizing a pig and a chimp is like taking half the dancers from a performance of Swan Lake and the other half from a performance of Giselle and throwing them together on stage to assemble something. It’s going to be a catastrophe.”

    I object!

    More like Swan Lake and a mosh pit, perhaps?

  9. #9 Trottelreiner
    July 6, 2013

    @ruth:

    personally, i think mixing the ensembles of swan sea and a mosh pit might be an interesting project somewhat akin to the somewhat discredited trope of the hopeful monster, but i guess my, err, refined tastes in ballerinas are not that on topic.

  10. #10 Ross
    New Zealand
    July 6, 2013

    If chimp and pig produces human, does human and pig produce hillbilly?

    I suspect the main problem of the author is trying to fit everything into the period since 4004BC.

  11. #11 Anon
    July 6, 2013

    Slightly off topic, reading that chart I was surprised to see where the bats were. I remember hearing somewhere they were more closely related to primates. Maybe that was an old, discredited theory, though.

  12. #12 David Marjanović
    Museum für Naturkunde
    July 6, 2013

    Maybe that was an old, discredited theory, though.

    Exactly: it looked like a good idea 30 years ago, but more recently discovered data – including all molecular data, which weren’t known back then – don’t fit it at all.

  13. #13 Ichthyic
    July 8, 2013

    It would be nice if AAH and MFAP annihilated one another, but I fear a hybrid theory involving dolphins.

    wasn’t that yet another Southpark episode?

    something about Dolphins and genocide and Japanese fishermen…

  14. #14 Ichthyic
    July 8, 2013

    Despite rumors of some experiments that attempted to test that, though, there have been no human-chimp hybrids observed, and I think they are highly unlikely to be possible.

    …but see Sean Cullen:

    http://vimeo.com/21701914

  15. #15 Merv
    UK
    July 13, 2013

    MFAP ?

    If PZ had taken the time to read the full account on MacroEvolution.Net, he would have realised that the most likely hybrid parents are a male pig and a female chimp. Hence PFAM would be a more appropriate nomenclature if one has to resort to crude language

  16. #16 Brian
    July 14, 2013

    No note for or against the hybridization theory, though I do find it a compelling read – but worth addressing is this:

    “If hybridization in mammals were so easy that a pig and a chimp could do it, human-chimp hybrids ought to be trivial.”

    Before we write off heavier-than-air flight, we might want to test it out first. How many failed experiments have there been so far to mate chimps with humans… or is the scientific method old hat these days, and we’re now going on faith?

    The last time we had a far-fetched origin story for mankind, it took decades for people to start believing that humans might really be descended from apes, as unbelievable as it sounded…

  17. #17 Trottelreiner
    July 14, 2013

    As the old joke goes, it’s quite unlikely humans and farm animals could create hybrids. We would know by now, especially with some “lone farmer on a mountain” groups…

    (Resists from going after Scottish, Australian or New Zealandian, ducks and runs for cover…)

  18. #18 David Marjanović
    Museum für Naturkunde, Berlin
    July 15, 2013

    If PZ had taken the time to read the full account on MacroEvolution.Net, he would have realised that the most likely hybrid parents are a male pig and a female chimp.

    Well, no, that’s not likely at all.

  19. #19 Green Eagle
    July 16, 2013

    I believe you haven’t though enough about this issue. While they amount to two persons, and not one, I can remember a few years back when the American people elected a chimp and a pig to lead the country. Surely this is some evidence that chimp-pig mating is possible. and that many of their offspring have the right to vote.

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