Difference between the skin of seals and humans

Clearly human skin is very unlike that of hairless aquatic mammals; this waterlogging of the skin in humans is why your fingers wrinkle in water. The specialized skin of these seals is what allows the sebaceous gland to provide its waterproofing function. That these glands are incredibly different in seals compared to humans and other primates can also be seen by examining their life history, which you'll see in the section on sebaceous glands below.

"Aquatic eccrine sweating"

From Elaine Morgan 1990:94, The Scars of Evolution Souvenir Press: London:

"There is even one clear aquatic instance of eccrine sweat-cooling. When the fur seal goes ashore to breed it suffers from the heat because of its double insulation of fat and fur. It is believed to be descended from a possibly dog-like land-dwelling ancestor with foot-pads of the standard mammalian type: the flippers are covered with eccrine glands which sweat profusely as it waves them in the air to cool itself."

"James Borrett asked me for a reference to the statement I gave that harp seals use eccrine glands for thermoregulation. I was quoting from memory, and I'm sorry I got the wrong seal. It is the fur seals that do this. When they haul out and are overheated on land they sweat through eccrine glands on their naked flippers."

"The reference is: G. A. Bartholomew, in 'Vertebrate Life', McFarland et al, London: Collier MacMillan, l979, p.773"

This is the ref I mentioned in my opening page; we find that Morgan has provided not so much an actual reference but instead a "find a reference" kit (assembly required). First you have to find the book she got the reference from, because that's all the info she gives. Once you find the book, you can look for the actual Bartholomew reference. When you find that, what you find is that you are actually looking for Bartholomew and Wilkie's 1956 article in Journal of Mammalogy 27:327-337. Now you can embark on looking up the actual reference.

Now when we look at the reference Morgan has given, we find an interesting thing: there is no mention whatsoever of eccrine sweat glands. This is not especially surprising if you realize that seals have no eccrine sweat glands at all. Why does Morgan assume, contrary to fact, that seals have eccrine sweat glands? The answer undoubtedly lies in her oft-stated belief that apocrine glands disappear in aquatic species (this was a long-held cornerstone of her version of the aquatic ape hypothesis). Seals, however, are well supplied with apocrine sweat glands (Scheffer 1962; Ling 1974; Sokolov 1982; King 1983). Note that reference "Sokolov 1982" is a book which Morgan uses extensively -- when it suits her purposes.

In fact, in the Bartholomew and Wilkie article, as in the book Vertebrate Life, the authors don't even actually notice sweat on these seal flippers (which Morgan claims "sweat profusely"). They actually mention that the seals wave the flippers about, and that the flippers are "abundantly supplied with sweat glands" (which we've already seen are apocrine rather than eccrine sweat glands). Is there actual evidence that these seals' flippers produce any sweat at all?

In a 1965 article in Nature (which Morgan cites in The Scars of Evolution), John Ling mentions the evidence for actual production of sweat due to heat in these seals: "the appearance of liquid droplets on the glabrous palmar surface of the northern fur seal, Callorhinus ursinus (L.), after exposure to radiant heat was assumed to indicate that sweating had been induced" (Ling 1965:561). His reference is the 1962 work of Victor Scheffer, in which Scheffer describes the experiment that led to this conclusion:

"When a heat lamp is focused on the naked flipper of a freshly killed seal, the black epidermis soon begins to blister. Before it does so, droplets appear on the surface of the skin in a fairly regular pattern. These are assumed to be secretions of the sweat glands." (Scheffer 1962:7)

So the evidence shows that if you fry a dead seal flipper until it blisters, the apocrine glands exude fluid. This is what Morgan claims is "one clear aquatic instance of eccrine sweat-cooling".

Discussion

In this section we see another example which demonstrates that Morgan's claims are based on, at best, really poor research. This is not an isolated example; we can see this in her claims about sodium, emotional tears, and salt glands. In all these instances she has made claims that are contrary to the facts, and indeed has done so even when the facts are contained in the very source she inaccurately cites. She also persists in making phony claims even after facts (with references) are pointed out to her (for instance regarding salt glands being present in terrestrial birds and reptiles as well as in marine forms). This is either the mark of a dishonest researcher or an incredibly poor researcher. Yet it is this standard of research and evidence Morgan offers as a reason to throw out the last quarter-century of paleoanthropology.

For anyone familiar with Morgan's published and online writing, it is also evident from this particular reference that her standard of evidence for her own theory is far less stringent than what she expects from all others.

Morgan has often made the claim that apocrine glands are more efficient for cooling than eccrine glands, but ignores the advantage of eccrine glands. Apocrine glands discharge their contents and these must be replenished before they're used again, while eccrine glands can go on and on. This allows humans a huge endurance advantage over apocrine sweating animals. The famous example of !Kung hunters running down a giraffe is an example of this advantage. The giraffe's apocrine glands work for only so long before they must recharge, and then the animal must rest or become overheated; this allows the far slower but steadier humans to outlast it and run it down. But does this mean that humans must always be near water? Note that both among the !Kung and Australian aborigines, hunters would often go on long treks far from water without carrying any water, and this in far drier country than our ancestors lived in. Even in the strawman version of savannah ("arid, treeless") that Morgan and other AAT/H proponents use, carrying water would be unnecessary.

Marc Verhaegen makes his own "seal sweat" claim

One thing I will say for him: his reference is relatively clear by AAT/H advocates' standards and even refers to the page numbers. On the other hand, he often mistakenly claims that the mammal in question is the Northern Fur Seal (it isn't), and he often makes the same mistake Morgan does of saying these are eccrine glands (they aren't). He has sometimes used the same bad reference that Morgan used in the above example, and he apparently often confuses the two references. But he seems to have settled on a different reference once people started, apparently with the help of this site, pointing out the problems with the other one. This certainly adds confusion to the story, but nothing we can't manage; so it's time to hit the library.

First thing here is to give ourselves some extra time, because Verhaegen's now-preferred reference is "p.87-88 in AR Hoelzel ed.2002 'Marine mammal biology' Blackwell". The reason for the extra time is that this is obviously a generalized textbook (just as Morgan's reference was), not a journal or other volume where we'd be more likely to find the primary data one needs to make the claim that Verhaegen did. So we need to get the textbook, then find the papers that the textbook refers to. How do we know that there's going to be more of a search? Call it intuition, or experience, or just look at the general statement that Marc quotes, the one he claims says that sea lions are second only to humans in sweating: "sweat glands on the flippers of otariids aid in heat transfer. On hot days sealions & furseals can often be seen fanning their flippers & increasing evaporative heat loss at these sites". Now note what this statement doesn't say -- it doesn't say anything about how much sweat sea lions produce, whereas Marc obviously wants us to think it does. So we know that after we get the book, we're also going to have to find the further studies that the book refers to, the ones Marc didn't mention and probably didn't read. Note too, if you have a critical mind (and in science you'd better have such a mind) that it looks like Marc left something off the front of that first sentence. I don't know about you, but I want to know if he did, and if so, what it says. So we're off to the library.

Okay, got the book, and here's the pages; turns out this is Chapter 3 of a general textbook on marine mammals, this chapter by Terrie Williams and Graham Worthy from UC Santa Cruz and U of Central Florida, respectively. And Marc got the quote right, but there are two words missing from the front of that first sentence. The words are "In addition". That's interesting, because they're obviously talking about sweating not being the be all and end all of thermoregulation you'd expect it to be in the second "most-themoregulatorily-sweating" animal in the world. The part before the sentence is the bulk of the paragraph and talks about the really neat blood vessels many pinnipeds have in their skin, especially around their flippers. These are called AVAs (arteriovenous anastomoses) and what they do is open and close off blood flow to either conserve or disperse heat -- blood gets hot as it travels through the body and the blood vessels cool off when they're near the surface rather than when they're deep in the body core, so if a seal needs to conserve heat, it restricts these AVAs, and when it needs to get rid of heat, it opens them up. It works exactly like a radiator, and is a critical part of thermoregulation in seals. In addition, they sweat... but how much? Must be a lot to be the second "most sweating", since we know that other mammals, such as horses, etc., manage to sweat away their heat in very hot conditions. So does this textbook say something about it, some numbers maybe? Why yes, it does, and look at that, it says it just after the section that Marc quoted. I wonder why he didn't quote that sentence?

Oops, I see why. It seems they don't sweat very much at all: "Evaporative cooling resulting from both sweating and respiratory losses accounts for less than 20% of heat production in California sea lions studied under experimental conditions (Masuura & Whittow 1974; South et al. 1976)." That's not very sweaty. It turns out that sea lions really don't sweat very efficiently or effectively at all. We can go to the next step now and get some more facts and figures, from the references the textbook cited, the ones Verhaegen probably didn't bother to read (we know he didn't tell us about them).

This is exactly the sort of thing one needs to look at, especially when the text contradicts what you're claiming, as this textbook contradicted Marc Verhaegen's claim. The two studies referenced are slightly different in their goals; the South et al. study was aimed at finding out much of the heat that sea lions did lose was due to evaporative cooling (not just sweating but panting, and other techniques I'll mention later) and how much due to simple radiation and conduction-convection (this latter with the help of those nifty AVAs). The Matsuura and Whittow study was aimed at finding out how much of the heat the animals needed to lose actually could be lost through evaporative cooling.

I'll start with the South et al. article: Sea lions, like other otariid seals (eared seals) just can't get rid of the heat they produce and absorb even through panting and sweating combined -- under fairly typical conditions of 15-20 degrees C (about 60-70 deg F) those two methods combined can only lose about 20% of what they do lose and in fact in really hot conditions they do a sort of ersatz "sweating" by drooling all over themselves and urinating on themselves (hey, it's not easy for other animals to stay cool) and even with that to help out they can't do the job with evaporative cooling (it can nudge them up toward 50% of the total they lose but only under pretty hot conditions -- 28 degrees C, or about 80 deg F). Even with all that -- panting, sweating, and drooling and urinating on themselves -- the test animals just can't lose enough heat (more on that when we get to the next article) and so had a "precipitous rise in body temperature" which resulted in stopping the experiment. The seals were lying prone and panting heavily -- they didn't want to kill them. By contrast, we see that non-human primates, and horses (and certainly humans), among others, certainly manage much hotter conditions than that without taking to the water, which is ultimately how sea lions and other seals ordinarily handle a high heat load -- they hit the water before they hit the temperatures used in that test.

The other article referred to in the textbook also measured sea lion evaporative cooling, in this case to see how much was due to panting and how much to sweating and how much of the total they needed to lose could actually be lost through this combined method. They measured the sea lions at temperatures between 13 and 30 deg C (about 55-85 deg F) and found that the heat loss due to evaporation (both panting and sweating) was a bit under 20% of the heat produced by metabolism, which they note was "relatively ineffective" (the harbor seal they tested did even worse). The South et al. article emphasized that this amount was at least something, even if it wasn't nearly enough. The Matsuura and Whittow study showed that about 16% was due to sweating and about 2.5% due to panting. The conclusion has several statements that are directly apropos to Marc's claim, which makes it a pity he didn't look at either of these primary sources which would've showed him his error. Let me quote:

"The total evaporative water loss from the sea lions in a warm environment could account for the dissipation of less than 20 per cent of the heat that the animals were producing. In contrast, many terrestrial mammals and birds are able to lose heat equivalent to their entire heat production by evaporation of moisture (Dawson & Hudson 1970; Hart 1971; Dawson 1973). If the minor sweating responses of pinnipeds are the legacy of their carnivory ancestry (see above), then the ineffectiveness of evaporative cooling mechanisms largely represents the absence of panting or of saliva spreading, in pinnipeds as opposed to terrestrial carnivores." (pp.18-19)

and:

"The absence of effective evaporative cooling mechanisms in sea lions has been discussed elsewhere (Whittow et al. 1972; Whittow 1973). Teologically, sea lions may attempt to conserve water rather than to maintain a constant body temperature. In the course of their adaptation to the sea, dehydration may have had a role in suppressing the evaporative cooling mechanisms that ancestral pinnipeds may have possessed." (pg. 19)

Discussion

As with Morgan's "eccrine sweat" claim examined above, we see another example in which demonstrates an AAT/H proponent's oft-repeated claim turning out to be based on, at best, really poor research. Worse, the information that contradicted the claim was contained in the same chapter that Verhaegen quoted from, one very short sentence after the sentences he quoted. This suggests that Verhaegen must have seen the clearly stated contradictory statement, but simply didn't report it. This in turn suggests that the fact he didn't do so was not an accident. And that, readers, is not good.

Even if you fully intend to do a good job and report the whole thing, unlike Marc's expurgated version of his reference, you have to watch out when you use a general textbook like this one. Mind you, I read more of it and it's a good book by good people, but even good people can make mistakes, and Williams and Worthy made one with the reference they gave for the first sentence that Marc quoted (he left the references out of his quote). The statement that Williams and Worthy make about seals flapping their flippers is "supported" by what can only be an error, since the article they refer to (Blix et al. 1979) makes no such claim and is in fact only about how newborn harp seals manage to keep from freezing since they're born on ice floes in the wintertime (short story on that: they shiver a lot). But I know from actual sources (Bartholomew and Wilkie 1956, for instance) that seals do in fact wave their flippers when they get hot (this isn't a controversial statement, and doesn't actually need the degree of support a controversial or new statement, like Marc's sweating claim, needs). But this does point out the danger of using secondary references, especially for information that's either not widely known or well established. Authors sometimes make mistakes, as Williams and Worthy obviously did here.

But how do we know that Verhaegen didn't also simply make a mistake with his claim? If he had, it might be embarrassing that he has made his incorrect statement many times using references that don't support it, but it would still be simply a mistake, no matter how substantial or embarrassing. But in fact we know that it wasn't a mistake, because the information that contradicted his claim was not only in the same book, and not only in the same chapter, and not only on the same page, but actually in the paragraph immediately after the sentences he quoted. He couldn't have missed it, and that means it definitely wasn't a mistake that he didn't mention it, it was deliberate. So we can see he claimed the reference said something when it actually said something completely different, and he did this deliberately.

Sebaceous Glands and the AAT/H

There's the fact that many aquatic mammals -- whales and manatees, for instance -- have either no sebaceous glands or only a very few, very rudimentary, ones.

There's the differences in seal skin (where they can provide waterproofing) and humans (where they can't) as noted above.

Finally, the features of sebaceous glands in humans suggests they are a sexually selected feature, as is common in mammals. There is a large difference between male and female humans in the number of their sebaceous glands. Males have a lot more of them -- as they do apocrine glands, which are also used as a sexual "lure" -- and complimenting this, females have better scent receptors.

This view of sebaceous glands also makes sensible another otherwise insensible fact -- their life history, ie. the age at which sebaceous glands initially become active:

In mammals which also utilize sebaceous glands in waterproofing skin or fur, these glands are numerous and become active by the time this feature is needed. In seals, for instance, they are active at birth. In humans, on the other hand, sebaceous glands are incredibly scarce until puberty and they only become active at puberty.

These facts leave us with two alternatives:

1.  The "aquatic" hominids didn't use their environment until puberty, and females didn't use their environment nearly as much as males; or

2.  The sebaceous glands of humans are a sexually selected trait as in other primates and many other mammals.

The second alternative is the only sensible one, and it's bolstered not only by the features of sebaceous glands, but also a lot of research on pheromones in relation to sex.

In this, humans are like other primates and many other terrestrial mammals, not like aquatic mammals.

How does Elaine Morgan respond when facts like these are pointed out, facts from a source she used as evidence even though it didn't say what she claimed it did? It's instructive to see; I mentioned the above facts about seal sweat in the sci.anthropology.paleo newsgroup, and this part of Morgan's reply shows how she either misunderstands or misrepresents information from an accurate source.

Elaine Morgan post (sci.anthropology.paleo: 10 Dec 1995):
EM> I am glad you have been reading Ling. Did you enjoy the bit on page
EM> 562 about how "the need for waterproofing the skin is met by enlarged
EM> lipid-secreting sebaceous glands"? Did it remind you at all of the
EM> way humans have very numerous greatly enlarged lipid-secreting
EM> sebaceous glands which none of the other apes possess? Isn't that
EM> interesting?
EM> Elaine

There are other problems with the hypothesis, which Morgan has made many times, that the sebaceous glands in human skin have waterproofing functions as seen in seals. One is that this hypothesis would require that infants and children forego this waterproofing -- a disastrous adaptation, to say the least; women also tend to have much smaller sebaceous glands. Further, the structure of seal skin is quite different than human skin; human skin doesn't have the hard outer layer that allows seals to be waterproofed by their sebaceous glands (see King quote above). Another tip if you want to do useful science: A hypothesis which is contradicted by facts which are well known at the time the hypothesis is constructed is a hypothesis which shouldn't see the light of day.

Conclusion

References

1962 Pelage and Surface Topography of the Northern Fur Seal, by Victor B. Scheffer. North American Fauna, Number 64, U.S. Fish and Wildlife Service.

1965 "Functional significance of sweat glands and sebaceous glands in seals", by John K. Ling (Antarctic Division, Department of External Affairs, Melbourne, Australia). Nature November 6, 1965, 208(5010):560-562.

1974 "The Integument of Marine Mammals", by John K. Ling. In Function Anatomy of Marine Mammals, Volume 2, edited by R.J. Harrison. Academic Press: London, New York, San Francisco.

1974 The Structure and Function of Skin, Montagna and Parakkal, Academic Press

1979 Vertebrate Life (3rd edition 1989), by Pough, Heiser, and McFarland Macmillan Publishing Company: New York and Collier MacMillan Publishers: London.

1982 Mammal Skin, by V.E. Sokolov. University of California Press: Berkeley.

1983 Seals of the World (2nd edition), by Judith E. King. British Museum of Natural History, Oxford University Press.

1985 Social odours in mammals, Volumes 1 and 2, edited by Richard E. Brown and David W. MacDonald, Claredon Press: Oxford.

1974 "Evaporative heat loss in the California sea lion and harbor seal", D.T. Matsuura and G.C. Whittow, Comparative Biochemistry and Physiology, vol. 48A, pp. 9-20

1976 "Air temperature and direct partitional calorimetry of the California sea lion (Zalophus californianus)", Frank E. South, R.H. Luecke, M.L. Zatzman and M.D. Shanklin, Comparative Biochemistry and Physiology, vol. 54A, pp. 27-30

1979 "Some aspects of temperature regulation in newborn harp seal pups", Arnoldus Schytte Blix, Hans J. Grav, and Keith Ronald, American Journal of Physiology, vol. 236B (Jan-Jun) pp. R188-R197 (not apropos to this discussion as it's about baby seals staying warm rather than anything about cooling but included here so you can check me out if you wish)

2002 "Anatomy and Physiology: the Challenge of Aquatic Living", Terrie M. Williams and Graham A.J. Worthy, (relevant pages, pp.87-88, Chapter 3 in Marine Mammal Biology, A. Rus Hoelzel, ed., Blackwell Publishing