Jim Moore's "AAT Sink or Swim?" Web Site
AAT Claims and Facts: Breath holding


On this page Moore, rightly perhaps, calls Morgan to task for over-stretching the argument of breathing control as a an aquatic adaptation. Clearly any terrestrial mammal that has been exposed to the possibility of drowning at some point in its past would have benefited from the ability to swim to a certain extent and as a consequence of that activity, the ability to hold its breath would have doubtless evolved too. That humans can do so is probably not such a remarkable phenomenon as Morgan has implied.

It is fair criticism that Morgan has, perhaps also, over stretched this argument over the years with the arguments surrounding the descended larynx. I am told that even koala bears have a larynx that might be described as 'descended' and several aquatic mammals have a larynx that is best described 'ascended'.

However, Morgan has never suggest that diving reflex was unique to only humans and aquatic mammals, although, oddly, Moore claims she did. (Why would he do that?)  It seems that over twenty years later, the most sensible paragraph that has been written on the subject of the diving reflex remains Elaine Morgan's treatment of it in 'The Aquatic Ape Theory' 1982:

"He [Man] shares, for example [of aquatic adaptations], the 'diving reflex'... Sudden immersion also produces some heart-rate reduction in many land mammals: it is the degree of bradycardia which distinguishes the aquatics... . to achieve a comparison between man and apes in this respect would seem to be impossible. No non-human primate, such as a gorilla or chimpanzee, can ever be induced to put its head under water, let alone to dive, except by force. Under these circumstances, the consequent exertion, aggression and panic would affect the heart rate so as to render the experiment invalid." Morgan (1982:p77).

In other words, as with every so-called claim made by AAH proponents, the key comparison to make is humans with the great apes. When it comes to breath holding, there is just too little data to make any kind of good case one way or another.

Overall it has to be conceded that on this page, Moore does make the best case so far that Morgan has over-extended her argument. Practically all terrestrial animals seem to have some ability to swim and, as they do, then some level of voluntary breath control and apparent 'diving response' would be naturally expected.

Perhaps the argument that Morgan did not make clearly enough, apart from in the quoted paragraph above, was that the real comparison in this area should be made with the apes. As with swimming ability itself, humans appear to have something extra to offer compared to our nearest relatives. That is the observation, I think, that needs explaining. If Morgan did not make sufficient a case for it, then that is a pity. What is clear for all to see here is that Moore does not, indeed can not, make a case against it.

Breath-holding, the descended larynx, the diving reflex, and the AAT
Moore begins this page with a typical overstatement of the AAH position. He says "A common, ongoing claim by most AATers is that only humans and aquatic animals can hold their breath, that the human descended larynx (compared to other mammals) is an aquatic trait, and that only humans and aquatic animals exhibit the diving reflex."

Let's take that statement apart, bit by bit. First: "Only humans and aquatic animals can hold their breath". Moore doesn't, again, attribute the claim to any exact source. A search through Morgan's books reveals a few statements pertaining to the subject. She wrote "This [conscious control over the utterance of sound] has been achieved together with the conscious control of breathing, which is a feature of, and essential to, all diving mammals." Morgan (1982:p102) but no hint there of an exclusive claim. Perhaps Moore had a later statement in mind on the next page: "If a pre-human hominid, in the course of learning to swim and dive, had acquired conscious control over breathing and vocalisation for the first time in primate history (my emphasis), then the overwhelming difficulty hampering the development of the vocal channel would have been removed." That, is, I agree, getting near to the mark, and I would probably disagree with Morgan about it, but even that is not the same as Moore was arguing: that only humans and aquatic animals can hold their breath.

In 'Scars of Evolution' she writes "Homo sapiens, unlike apes and most land mammals, acquires conscious control of breathing at an early age" (Morgan (1994:p139) and in her latest book she wrote this "Generally speaking, this [breathing control] is not a matter over which mammals need to have conscious control, any more than they need conscious control over the secretion of their gastric juices, or the peristalsis in their intestines" Morgan (1997:p138.)

Now I don't mean to split hairs but Moore's statement isn't quite what Morgan has said. He's probably correct to argue that Morgan has pushed this argument a little too far. But very little real scientific study has been does on this area  and it is difficult to determine if an animal's breathing was under voluntary control in any case. 

The next part (about the descended larynx) appears a fair portrayal of the AAH position because it qualifies the claim with "compared to other mammals", but the last part, once more, overstates the case: "only humans and aquatic animals exhibit the diving reflex."

This extreme point of view is not what Morgan, or any AAH proponent, has argued, however.  In 1982 she wrote "He [Man] shares, for example [of aquatic adaptations], the 'diving reflex'... Sudden immersion also produces some heart-rate reduction in many land mammals: it is the degree of bradycardia which distinguishes the aquatics... . to achieve a comparison between man and apes in this respect would seem to be impossible. No non-human primate, such as a gorilla or chimpanzee, can ever be induced to put its head under water, let alone to dive, except by force. Under these circumstances, the consequent exertion, aggression and panic would affect the heart rate so as to render the experiment invalid." Morgan (1982:p77) Which would seem to be as fair a  statement on the subject as one could make. In her last book she was even more explicit: "And scientists came to realise that these [diving reflexes] were not confined to diving species: they are present in all mammals." Morgan (1997:p140) and "Thus, the fact that the diving reflex is manifested in humans is not in itself surprising or proof that our ancestors went through a semi-aquatic phase after the ape/human split." (Morgan 1997:p141)

It turns out that Moore has not been telling the reader the whole truth here. He has portrayed the AAH position to a level that is more extreme than that put forward even by its most vociferous supporter. Other AAH proponents might put it forward in an even milder way.

In the remainder of the paragraph Moore informs us that "the diving reflex is actually a universal trait found in all vertebrates" (Morgan told us that herself) and that "non-human, non-aquatic animals can and do hold their breath" (again, no doubt true, but notice how more misses out the word 'voluntarily' here.)

Breath-holding in non-human animals
Moore continues, as if the argument has been won already: "So contrary to the AAT claim, humans are not the only non-aquatic mammal which can hold its breath" even though, as yet, he has not provided any evidence to make his case. I suppose that the AAH claim was so grossly exaggerated that he felt confident enough to assume it was wrong already.

Moore writes "Various monkeys, for instance, can and do hold their breath..." not backing that statement up with any citation, "... and so do dogs", which is. On this Lin writes: "In dogs trained to voluntarily immerse their snouts in water, the bradycardia was immediate and pronounced, and the heart rate decreased by about 50% from the pre apnea value" Lin (1982 p275.)

I think it is quite clear that on this point Moore is right to show that any terrestrial animal with an ability to swim would be expected to have a degree of ability to hold their breath. In that sense this is a valid criticism of Morgan's argument which does appear to stretch this point a little to far.

But Moore's final point here "By the way, seals and whales don't hold their breath when they dive; they store oxygen in their blood, and actually expel the air from their lungs as they dive. This system -- radically different from humans -- is used by pinnipeds and cetaceans." somewhat misses the point. Whether the mammal expels the air before diving or inhales, they are still exhibiting voluntary breath control.

The real comparisons that matter here, are those with apes. Unfortunately there is very little evidence on that and, as Morgan wrote in 1982, there is little likelihood of it  appearing.

The Descended Larynx and the AAT
Moore makes a good point here that a partially descended larynx would still be helpful to a hominid forming ever more complex sounds long before any kind of full syntactic speech we might recognise had evolved. It's a good point but I couldn't find any sentence where Morgan indicates she would disagree with it. The AAH argument would be that the descended larynx evolved in part to help mouth breathing during swimming, but which clearly led to other spin off, notably speech.

Moore's counterarguments to this can easily be answered.

Firstly he argues that as the larynx isn't descended at first but takes a while to do so, (during which time the infant is learning to speak) any aquatic benefit would not be available to it for that period of time.
But this is no problem because, as with infant apes, it is highly likely that hominid infants were highly dependent (even more so than chimpanzees) on their mothers for locomotion. The infant would be less likely to go off swimming on their own than a chimpanzee infant would be to go off climbing in the first few months of life.

Secondly, he appears to argue that the fossil evidence (although he doesn't cite which) suggests that the descended larynx evolved much later than the originally proposed 'aquatic phase'.
Once again, not all proponents of the AAH support this 'post-LCA/Pre-Homo-aquatic' model. If one assumes that the ancestors of man were always living on the water's edge and began to swim and dive relatively recently, then this would be consistent with the fossil evidence.

Moore finishes this section with this: "Further, even some AAT proponents, such as Marc Verhaegen, have realized that this feature is not at all like the larynx of aquatic mammals. Why did Elaine Morgan claim it was for twenty some years? She's admitted she just didn't look at the evidence. Excuse me, but that isn't someone I want to buy a used theory from... "

So, is he now telling us that Morgan has retracted this claim after all? That's odd, because at the start of the page Moore advised us "I wouldn't hold your breath waiting for AATers to stop making this claim, though, cause for years it's been pointed out to them and they haven't stopped yet."

Apparently they (let's face it, Morgan) has stopped making this claim, but Moore is still criticising her for doing so. Isn't this yet another case of the pot calling the kettle black?



How about the diving reflex: are humans well adapted for diving?
Moore starts this, final, section, with the question: "Yes, we know humans can swim and dive, but so can other non-aquatic animals. Do humans show the adaptations that are found in animals with a lifestyle in which diving is important, as the AAT says it was for us?" The notable omission here is the comparison with apes. Yes, we know other non-aquatic mammals can swim and dive, but how well can the apes? That is the important question in all of this debate.

According to Moore "AAT proponents say they do, [in answer to his question] and that other terrestrial mammals don't show such responses as breath-holding and the "diving" reflex."

He then finishes by listing twelve separate citations of scientific writings showing that the AAH claim that breath-control and diving reflex was unique to humans and aquatic mammals is false.

This might look quite impressive to an impartial observer; Here's an AAH claim, they might think, that is clearly being taken apart by Moore in the best possible way, with citation and citation.

But when the citations are looked at a little more carefully it becomes clear that some of them are a little 'off the subject'.

The last four citations merely document that in aquatic mammals, sea otters, and pinnipeds, diving is preceded by expelling most of the air from the lungs before a dive. This is still a form breath control but, relies on a greater capacity of the blood to store Oxygen. More, for example, cites Bonner in describing how "A Weddell seal, for example, has about 150 ml of blood per kilogram bodyweight, about twice the value for Man. Furthermore, seal blood contains more haemoglobin than human blood -- about 1.6 times as much. The combined result of this is that the blood oxygen stores per unit of body weight is about three or three and a half times that of Man." Bonner (1990:p33-34)

It should be remembered that the AAH is not suggesting that man was ever as aquatic as a sea otter or a seal but, it is interesting to note that, compared to chimpanzees and gorillas, humans also have blood characteristics that are 'on the way towards' aquatic mammals from their ape cousins.
"As one of their physical adaptations to long periods of submersion, marine mammals have a reduced number of red blood cells per unit volume. They have large blood cells, with a higher haemoglobin content per volume per cell than is found in land mammals of comparable size (Lenfant 1969). In this respect it is remarkable that chimpanzees have an average of 7.3 million red cells per cubic millimetre of blood, gorillas 6.3 and humans only 5.1 million; the average size of the cells is about the same. The percentages of haemoglobin per cell are about 12.2 for chimpanzees, 13.2 for gorillas and 18.6 for Humans (Eberl-Rothe, 1960)." Fichtelius (1990:p288) 

The other eight citations merely give examples in the literature showing that non-aquatic mammals other than humans do also exhibit some kind of diving reflex (bradycardia etc) when subjected to trained or involuntary breath-holding.

But, hold on, Morgan told us all this herself, remember... "these [diving reflexes] were not confined to diving species: they are present in all mammals" Morgan (1997:p140.)

So why is Moore making such a big fuss about all of this here? The only explanation that seems to fit with the facts is that he is, again, just trying to misrepresent the AAH to imply that Morgan's work has been less than truthful.

Eberl-Rothe, G (1960)
Blutzellen. In Primatologia, ed Hofer et al. (Basel: Karger), vol 3: 1, 1-21.

Fichtelius, Karl-Erich (1991). More Thoughts on the Aquatic Ape Theory: How the aquatic adaptations of man differ from those of the gorilla and the chimpanzee. In: Roede, Machteld; Wind, Jan; Patrick, John; Reynolds, Vernon (eds.), (1991). Aquatic Ape: Fact of Fiction: Proceedings from the Valkenburg Conference. Souvenir Press (London)

Lenfant, C. (1969) Physiological properties of the blood of marine mammals. In The Biology of Marine Mammals. ed. H T Anderson (New York: Academic press)

Lin, Yu-Chong (1982). Breath-hold Diving in Terrestrial Mammals. Exercise in Sport Science Review Vol:10 Pages:270-307

Morgan, Elaine (1982). The Aquatic Ape Theory. Souvenir Press (London)

Morgan, Elaine (1982). The Aquatic Ape Theory. Souvenir Press (London)

Morgan, Elaine (1990). The Scars of Evolution. Oxford University Press (Oxford)

Morgan, Elaine (1997). The Aquatic Ape Hypothesis. Souvenir Press (London)