Aldosterone, water, and bipedalism

This is, as I mentioned, a fascinatingly thorny little thicket involving some persistent "false facts" begun by Elaine Morgan in her 1990 book, The Scars of Evolution, and repeated by others since. At its heart is a central contention of the Aquatic Ape Theory: a major reason that these water environments were necessary for the evolution of bipedalism is to help support the body weight of our ancestors while walking upright. Hardy made quite a point of this in his first article on the subject, and it has been a central tenet since. Morgan devoted an entire chapter to it in The Scars of Evolution (Chapter 3, "The Cost of Walking Erect", and part of chapter 4). It was there she brought up the aldosterone evidence...

Wait, just a sec... I can't keep typing without mentioning this. Sorry, but this one just slays me. Back when I was posting on this subject in the sci.anthropology.paleo newsgroup, Elaine made the most amazing claim. I have to mention it -- it's even apropos, since it sheds light on her research and debating style. Here's what she said about this on the 4th of July, 1995:

"I would like to reply to some serious misrepresentations.

"Jim Moore says that "all" (sic) supporters of AAT claim that a major reason for the evolution of bipedalism was that wading in water helped to support the body weight. I do not know of anybody that says this."

Frankly, I was astonished. I mean, she did get the theory from Hardy; she reprinted his articles on the subject in her 1982 book. Didn't she ever actually read his work? But more than that, what astonished me was that barely 5 years before she posted, she'd published an entire chapter and a half on just that point. Now, I've seen authors who were ignorant of writings that contradicted their position, and I've seen authors who were ignorant of writings that support their position, but I've never seen another writer who was so ignorant of what they themselves had written. Incredible.

1990 The Scars of Evolution Elaine Morgan. Souvenir Press: London

pg. 47:
In the aquatic scenario the position is reversed. Walking erect in flooded terrain was less an option than a necessity. The behavioural reward -- being able to walk and breathe at the same time -- was instantly available. And most of the disadvantages of bipedalism were cancelled out.
Erect posture imposes no strain on the spine under conditions of head-out immersion in water. There is no added weight on the lumbar vertebrae. The discs are not vertically compressed. (An astronaut in zero gravity gains an inch in height in space, and immersion in water is the nearest thing to zero gravity on planet Earth.)
pp. 47-48:
Water thus seems to be the only element in which bipedalism for the beginner may have been at the same time compulsory and relatively free of unwelcome physical consequences.
From these quotes you can see that the support provided by water is considered to be a critically important part of the purported aquatic transition to bipedalism. Despite Morgan's claim to the contrary.

Okay, I'm better now. Where was I? Oh yeah...

It was there (chapters 3 and 4 of Scars) she brought up the aldosterone evidence. Aldosterone is a hormone which regulates salt balance in the body (there's a lot of salt-related material in the AAT/H, and therefore on this site). Let's see what she has to say:

1990 The Scars of Evolution Elaine Morgan. Souvenir Press: London.

pp. 31-32:
"Endocrine glands sited above the kidneys produce hormones which respond to actual or potential physical 'emergencies'. The best known is adrenalin (epinephrine), the 'flight-or-fight' hormone. In situations arousing fear or anger it causes sugar to be released into the bloodstream supplying instant energy, plus clotting agents in case the situation leads to violence and bloodshed.
A hormone which responds to 'emergencies' of a different kind is aldosterone. Its function is to regulate blood pressure, and to inhibit the excretion of salt. The 'emergencies' which stimulate the production of aldosterone are listed in medical textbooks as:
1  surgery;
2  anxiety;
3  a diet deficient in salt;
4  haemorrhage;
5  standing up.
The first four items apply to all mammals and are readily understandable. If there is a deficiency of salt in the body tissues, aldosterone conserves salt by preventing its excretion into the urine. Loss of blood due to surgery or haemorrhage means that the blood volume must be restored; the action of aldosterone increases the fluid volume of the blood. As for acute anxiety, some of the physical manifestations (sweating, vomiting, loosening of the bowels) are notorious squanderers of salt reserves. An increase in aldosterone production will guard against all these contingencies, since this hormone can inhibit salt excretion in the sweat and faeces as well as in urine.
The fifth 'emergency' (standing up) applies particularly to bipeds. Rising from bed or from a chair produces a six-fold increase in the amount of aldosterone in the blood. This bears no relation to the amount of exertion needed to attain or sustain erect posture. Experiments have been conducted where a volunteer is strapped to a pivoting board which can be tilted on its axis, thus raising the body to the perpendicular with no physical effort involved. The production of aldosterone still rises just as steeply.
The explanation once again lies in the pull of gravity on the bloodstream. When we stand up, the blood tends to drain away from the head and the heart and pool in the lower limbs. It so happens that the main baroceptors which monitor changes in blood pressure are situated in the neck. For a quadruped this is a perfectly appropriate site; blood pressure at this point will be fairly representative of the pressure throughout the body; when these baroceptors register a change in blood pressure, they trigger appropriate responses such as increased output of aldosterone.
But the receptors are incapable of distinguishing between the 20 per cent drop in pressure which would result from a massive haemorrhage in a quadruped, and the 20 per cent drop in the head and neck region which signals in a biped the act of standing up. The aldosterone levels respond in the same manner to standing up as to surgery."
Now that sounds serious. Thankfully there's a solution at hand for those poor hominids:
pg. 47 (Ibid.):
"Standing up in water does not trigger secretion of aldosterone, salt retention or higher blood pressure. The reverse is the case: head-out immersion causes a prompt and marked fall  in systolic and diastolic blood pressure, plus increased excretion of salt in the urine."
Lucky little buggers. If only it were true...

The reality about the standing up "emergency"

As is common with Morgan research, it's hard to know where to start in pointing out errors; I think we'll start with her list, as "listed in medical textbooks". She left out a few key points. Before I get into particulars, maybe I should make a point clear. When I initially researched Morgan's statements in these chapters, I found she was wrong about many points, but I couldn't tell at that time whether she was wrong because she'd used references which were wrong or whether she had accurate references but misrepresented what they said. As a student of the history of science, I wanted to know which it was. So in December 95, in sci.anthropology.paleo, I asked her to provide those refs (she'd by that time said she was more than willing to do so), and eventually, she posted them. The refs were good, in fact, I had found them already in my own research on the subject. The list she got from the Encyclopedia Britannica, which I hadn't used but when I checked it out, it was the exact same list I'd found in William Ganong's 1993 Review of Medical Physiology. There are some interesting differences between the list in these books and the list in Morgan's book.

In her book, Morgan uses a rhetorical device which seems to be an attempt to get the reader to think that not just these aldosterone receptors, but the total animal would "respond in the same manner" to standing up as it would to massive hemorrhage or to surgery. But of course many other factors would enter in and create a massive difference between the two types of stimuli. Morgan, by carefully crafting the false context that these books consider all the items on this list to be "emergencies", fails to differentiation between several distinct types of causes of this aldosterone build-up. Both the textbook and encyclopedia article, however, point out that the actual emergencies  (surgery, anxiety, physical trauma, and hemorrhage) as opposed to normal bodily functions (like standing up, which Morgan inaccurately lumps in with the emergencies) and slow-onset illnesses, also cause an increased excretion of powerful steroids called glucocorticoids. They point out that these glucocorticoid levels are unaffected by high potassium intake, low sodium intake, constriction of interior vena cava in thorax, standing, and secondary hyperaldosteronism (in some cases of congestive heart failure, cirrhosis, and nephrosis).

While Morgan's list mixes together these normal life events (like standing up) and slow-onset diseases with actual emergencies and clearly implies that the sources call them all emergencies (as she does) the sources themselves don't do that. It was merely Morgan's invention.

The reality of water immersion

The second part of Morgan's claim rests on scientific experiments on the effects of water immersion therapies. She presents the results in the section on page 47 of The Scars of Evolution:
"Standing up in water does not trigger secretion of aldosterone, salt retention or higher blood pressure. The reverse is the case: head-out immersion causes a prompt and marked fall  in systolic and diastolic blood pressure, plus increased excretion of salt in the urine."
With these statements, Morgan completes her argument that our hominid ancestors would be able to stand up in water without the temporary effects of blood pressure drop and rise in aldosterone. Of course the effects of these changes when standing up are actually pretty minor, as even Morgan admits ("It is a system which works smoothly and is in general benign." Ibid. pg. 33), but perhaps a case could be made that things might have been easier for our ancestors without it. Morgan tries to make that case, as seen above, and it would make a lot of sense... if it were true.

You see, these changes during water immersion don't happen in time to prevent these very temporary effects of standing up, as Morgan suggests. Her source, Murray Epstein (who actually is an experienced researcher on this subject) points out that the aldosterone drop during immersion Morgan is so happy to see isn't a quick one, as it would have to be for it to be a benefit in the aquatic ape scenario; instead it begins "as early as 60 min of immersion" (Epstein 1984. pg. 181). The increased excretion of salt Morgan mentions takes even longer to come about, several hours after the increased excretion of urine (which is why you can get dehydrated in water unless you can drink it; of course in the commonly postulated AAT/H saltwater environment you can't drink it). The increase in urine excretion itself doesn't happen for an hour or so after immersion either. Epstein also notes the blood pressure decrease isn't quite so dramatic as Morgan seems to imply ("water immersion is associated with a significant, albeit slight, decrease in mean arterial blood pressure", Epstein et al. 1978, pg. 495 [italics in original]).

These changes do not happen quickly, as Morgan suggests and as her scenario requires. They also don't happen unless you're in water up to your neck (or higher), which is also a problem for the wading aquatic ape. For the changes to have a helpful effect when we stand up, these bipedal hominids would have to always enter the water by crawling (or maybe scooting in on their rear ends) and then stand up only after an hour or so. Hard to see where that helps you in the common AAT/H scenario of running into the water to escape predators. Maybe they could scoot really fast.


1993 Review of Medical Physiology by William F. Ganong, M.D. (UCSF), Appleton and Lange: Norwalk, Conn. 16th Edition. (chart on pg. 343)

1984. "Renal, endocrine, and haemodynamic effects of water immersion in man", by Murray Epstein, Contributions to Nephrology vol. 41, Cardiocirculatory Function in Renal Disease, pp. 174-188.

1978 "A Kinetic Assessment of Aldosterone Responsiveness in Secondary Hyperaldosteronism and in Anephric Man", by Murray Epstein, Edgar Haber, and Richard Re, in The Endocrine Function of the Human Adrenal Cortex vol. 18, pp. 493-508.

Another interesting fact is that the reflex which causes all the above (the Henry-Gauer Reflex) is not present in seals. It's highly likely that it isn't present in other aquatic mammals, but that hasn't been studied, as far as I know. However, Morgan thinks it's evidence of an aquatic past, when the reality is that this is something we would expect to see eliminated by an aquatic past

2001. "Osmoregulation in Marine Mammals", by Rudy Ortiz, in The Journal of Experimental Biology vol. 204, 1831-1844.

By the way, in this section of The Scars of Evolution Morgan also attempts to contrast the hormone situation regarding adrenalin in humans with that seen in quadrupeds by intimating that other animals live free of stress by either predators or each other:

1990 The Scars of Evolution by Elaine Morgan. Souvenir Press: London.

pg. 33:
"A quadruped in a secure environment may spend weeks at a time stress free and with no need for these glands to be activated until the rutting season comes round."
Where on the actual earth would we find these quadrupeds which live in such a "secure environment" that they can "spend weeks at a time stress free and with no need for these glands to be activated"?  why has there never been a Nature show or National Geographic article about this predator-free Nirvana? what about the squabbling and fighting that goes on over food and water in most species?  has Morgan never even, say, fed ducks at a city park?