‘So’, you say, ‘we, the people, are descended from a population of apes that spent a few million years splashing about in the drink. A marvelous and welcome addition to the resume of any imaginative freediver, to be sure, but can you prove it?’ Swell theory, but let’s talk science.
All right, then. Attorneys for all parties to the evolutionary debate ( the Creationists are not named in this brief) have stipulated that way-back-when, there existed a primate species we’ll call LCA – the Last Common Ancestor. It lived in the lush African forests. The last common branch in the family tree of humans, gorillas, chimps and bonobos. Then stuff happened, natural selection did its thing, and now one species turns the crank and another dances.
The Standard Theory, the one you’ll be taught at Oxford, says that some populations of the LCA got to be spending more time in the wide open spaces ( the savannah) that came into being at some point, and that adaptation to the grasslands made us as we are today. Forest – to- grasslands – to- Club Med.
The Aquatic Ape Theory (AAT) says that what happened to the LCA groups that became our ancestors was that they got to be spending a lot of time in and around water, did some adapting to those conditions, and then reverted to the dry life. Forest- to- waterworld- to- grasslands- to -Club Med.
So, which theory does science prove to be true ?
Here’s the thing, my fellow aquanauts and only friends: science (the one with the lower case ‘s’) is not in the business of proving theories to be true. In fact, science’s definition of itself says flat out that it cannot prove a theory to be true. Rather, science is about proving theories to be false, and regarding competing theories as Best of Show while vigourously trying to prove them false, too.
So what good is science if it can’t prove its own theories ? Well, it turns out to be helpful to have understandings which are pretty good, even if imperfect. We see and act according to our best current understanding of things – because, literally, we don’t know any better. It works. It has gotten us neoprene, antibiotics, the Boeing 747 and the electric guitar, among other things.
Okay, then how do we decide a theory is bogus, so we can drop it or modify it or take it out and shoot it behind the barn ?
One input is the evidence, Dr. Watson, the evidence. If, for example, we have a nice theory that says heavy objects always fall faster than light objects, and we observe a case of a light object falling faster than a heavy object, we might, if we determined the observation to be reliable, be inclined to revisit the theory.
More complex theories, like the AAT, are a little harder to falsify in this way, by counterexample. If we say that a particular characteristic of homo sapiens, say for example face-to-face copulation, is the consequence of an aquatic interlude in the species’ evolutionary history, producing another primate species that also copulates face-to-face but for which there is no other evidence of an aquatic past does not shoot the AAT down. An anatomical, physiological or behavioral characteristic can, in principle, serve multiple functions and can, therefore, have been an adaptive response to a variety of selective pressures.
Sometimes we get tipped off when new data shows our theory to be at odds with some other, more basic theory which has withstood so much pounding over the years we treat it as if it had been proven true. For example, we are pretty sure that in order for A to have caused B, A had to come before B. We don’t like the idea that something that happened today caused something to happen yesterday. This is almost beyond dispute: it devolves from our definition of ’cause’.
So, if we have a theory that says, for example, that adapting to the conditions of the savannah caused some groups of LCA to stand upright and walk on two legs, a discovery of fossil evidence of bipedalism predating the emergence of the savannah ought to call that one into question.
Sometimes we find ourselves in a state where we have two or more competing explanations for what we see, and we cannot manage to find enough evidence to trash any of them. What then ?
Here, the principle of parsimony is brought to bear. Parsimony suggests that whichever theory has the fewest untestable assumptions should be the one we work hardest to falsify with data. Please note: parsimony does not declare that this theory is the ‘truest’ or the one most likely to be true, rather, it makes the self-evident point that focussing on the most parsimonious theory is generally the most cost-effective, efficient way for science to proceed. Big difference.
Now let’s talk aquatic apes.
The AAT offers itself as a parsimonious account of the startling existence of a very, very distinctive species of primate on the earth. Us. The AAT shares a big, basic assumption with several of its competitors: natural selection as the mechanism by which species are differentiated. The AAT and all of its competitors are trying to answer, in evolutionary terms, the grand question: Why is this ape different from all other apes ? How is it that humans, gorillas, and chimps all hail from the LCA but now have such drastically different tastes in evening wear ? The AAT offers a very simple answer: water.
The AAT encompasses a cluster of human anatomical, physiological and behavioral characteristics. Some of these characteristics are said to distinguish humans from most or all other primates. Others are said to be generally associated with aquatic animals. Some are said to meet both of these criteria.
Some key examples of the characteristics of interest to the AAT are:
Human Hair: Unlike the other primates, our bodies are relatively hairless, recent disturbing observations on Miami Beach notwithstanding. In addition to the lesser quantity of fur, ours grows out in patterns suggesting optimization for streamlining in water, whereas the other primates’ fur grows out ‘against the flow’. Most other ‘naked’ mammals are aquatic, although not all aquatic mammals are ‘naked’.
Fat: We ar fatter than the other primates, moreover, the composition and distribution of our body fat are similar to those of aquatic mammals. Fat is an excellent thermal insulator in water, and also provides buoyancy.
Breathing: Alone among the primates, we are able to assert conscious control over our breathing. An associated anatomical feature is also unique: our descended larynx, which has all sorts of disadvantages ( choking on food, exposure to infection, sleep apnea) but allows us to take in large quantities of air very quickly, through our mouths. Elaine Morgan is currently much intrigued by the prospect that alone among the primates, we gasp when startled. A pretty good reflex to have in a place where sudden submersion is a frequent flight-or-fight event: getting hammered by surf in the impact zone, escaping a predator, slipping while wading, etc. Getting pulled under by a current or a predator….
Hmmmm. Hairless, blubbery mammals, streamlined and able to take deep, big breaths: seems like a good start at designing an aquatic critter. Reminds me of most of my best friends. There are a whole host of additional characteristics that link to the AAT, too, a partial list of which might include:
Our blood composition, in terms of red blood cell counts and hemoglobin levels, seems more like that of aquatic mammals than that of our landlubber simian cousins.
We do a lot of face-to-face mating, much like some of the marine mammals and unlike most primates. How cool is that ?
Our brains are famously big in relation to our bodies, and some have suggested the development of such an expensive ( in terms of maintenance) thinkum was made possible by the abundant supplies of food rich in the balanced (1:1) omega-3 and omega-6 fatty acids. Fish. Kind of hard to come by on the savannah…
Human infants are remarkably adept in the water, seeming to have mastered apnea and swimming in ways that would make many adults blush.
We are the only primates that shed tears without any physical irritation to the eyes, and our tears contain large amounts of germicidal immunoglobin -A and lactoferrin: is our weepiness an adaptation to an environment in which water frequently washed away this vital defense ?
Real estate: don’t delude yourselves. Waterfront property is always more expensive, because people like being by the water. It is a very deep, hard-wired preference. You’ll never go broke investing in beachfront.
Curiously, the much-ballyhooed Mammalian Dive Reflex is not a keystone of the AAT. It ought to be obvious why: it is, as the term suggests, common to all mammals, and therefore does not distinquish those with recent aquatic pasts. However, the reflex is known to vary in intensity from species to species. It would be useful to know whether it is more intense in humans than in the other primates, but so far nobody has had much luck getting apes to dive, recent reports from Cyprus notwithstanding. Actually, maybe that in itself tells us something !
A great deal of the enthusiastic public discussion of the AAT focusses on this or that trait-du-jour : the pros and cons of single characteristics as ‘proof’. It is all interesting and helpful, however, it should be clear that no single element of the AAT is essential to its validity. Rather, the AAT’s elegance and power rest upon the simplicity with which it accounts for the whole cluster of things that are more or less special about people.
Research may well reveal simpler, better alternatives for one or more of the ‘aquatic’ characteristics, but so far the theory as a whole remains a serious and robust candidate for our Standard Theory. Science, alas, is as political an enterprise as any other, and as subject to human foibles such as vanity, insecurity, and jealousy. Hubris. Inertia and Sloth.
I’m no different. I favor the AAT because it is beautiful. I hope science knocks itself out trying to disconfirm it. I want to be descended from aquatic apes.