Theory that humans underwent a semi-aquatic phase at some point in their evolution. First proposed by Sir Alister Hardy in the 1950s, and taken up in the 1970s by Elaine Morgan in books such as The Descent of Woman and The Descent of the Child. Sometimes known as AAT.

A highly plausible and convincing theory to some, a load of nonsense to others. Has gained many adherents but is by no means the majority view, which is still basically that we came down from the trees in the savannah and learnt to throw things and became hairless for some such reason.

The beach-dwelling phase, if it occurred, probably occurred while we were all on the shores of the Red Sea or some such environment, but one of the biggest problems of the AAT is that no precise sequence in the fossil record, or gap in it if a gap is needed, can be pointed to as exactly the right time for the phase to have occurred.

Evidence for, not all of which needs to be correct or convincing for the theory as a whole to be believable:

And no doubt more that I or someone could list (along with the inevitable vitriolic attacks)...

Additional interesting bits of human physiology used in the argument for the AAT are:

Noted human zoologist Desmond Morris has been known to support aspects of aquatic ape theory as well. Although he has a certain amount of notoriety, he has spent most of his life studying the human species as an animal.

The cause of the move from forests to seas was the hot, dry Pliocene period. The forests over most of Africa died out to only a few isolated areas; competition within the forests was too high, and man's ancestors were not suited to the hard life on the plains. So, the theory goes, we moved instead to the sea, where leopards and other predators were loathe to follow us.

A few more points backing up the theory:

After the Pliocene came the relative abundancy of the Pleistocene. Man then spread out back into the interior, using his newfound bipedalism, tool-wielding skills and intelligence to dominate the scene.

This is all very well and good, but the theory seems a little complex and unlikely - it involves a change of habitat from trees to sea to plains, all within a few tens of millions of years. All just special favours for us, the acme of evolution? It would stand up more if there were a few other species in which the same process can be seen. And there are.

  • The pig is another not-very-hairy mammal. Its relatively weak legs, fat, bouyant body, and wide snout suggest that at some time it took to the swamps, and evolved there. The body of a pig is similar to ours... there is the story of a former cannibal race who, of all western imports, enjoyed spam the best because of its similarity in taste to human flesh!

  • The rhino is yet another hairless mammal. While not as water-loving as the hippopotamus, it still enjoys long periods of river wading, and eats water plants.

  • Of all similar creatures, the elephant is the most striking. Its evolution is really quite remarkable - it is descended from a small pig-like animal, but then over the ages, grew to be the largest land animal in its era. It is very easy to compare it to another mammal whose size swelled remarkably over the ages: the whale. In water, large mass is not the problem it is on land. Indeed, it is a benefit, as larger creatures lose heat much more slowly.

  • Its anscestors also had peculiar tusks. Some had spade-shaped ones, perfect for digging in soft, waterlogged soil, but not much good in the plains.

  • The early ancestors of the elephants showed a movement of the nose towards the top of the head. This would have been uncalled for on land, but excellent in the water. Nowadays, of course, they have a trunk. And what use is a trunk? It's inefficient for grass eating (a long neck would be better), and unnecessary for tree browsing. But it makes a pretty good snorkel. Not to mention its use for picking water plants.

  • Elephants can swim very well, perhaps the best of all land animals. A whole group has been known to swim for six hours straight, and one particular individual has crossed distances of sea of over a mile. Elephants' feet are also webbed, although this is not particularly noticeable anymore.

  • Elephants have been known to cry when under emotional stress. Hardly any land creatures cry, and hardly any sea creatures don't. Notice that this indicates that they were past sea-dwellers like us, not just river-dwellers like the rhino or swamp-dwellers like the pig. Also notice the surprising case of parallel evolution; elephants and humans, both rare in that they are tear-producing land animals, cry in the same situations! It's not as if we are related - in fact we use completely different glands to produce the tears!

  • Elephants are more intelligent than similar land creatures. This makes them adaptable enough to live in a wide range of habitats. They also have a highly developed vocal signalling system - a 'silent' herd of elephants is usually chattering away in the infrasound range. As stated before, very few mammals have a sophisticated vocal language, and those that do are almost always sea-dwellers.
(I know I've talked about elephants as much as, or more than, humans in this writeup. However, I thought it was closely related enough to our own evolution to mention in this node)

While it cannot yet be proven, the Aquatic Ape Theory should be taken seriously. While it seems outlandish, it answers questions that cannot be answered by the traditional "savannah theory" of how humans evolved. The Aquatic Ape Theory, or AAT, was first proposed in 1960 by Alister Hardy in an article titled, "Was man more aquatic in the past?" but he abandoned the theory because fellow scientists ridiculed him for it. His theory proposed that the traits humans share with aquatic mammals could have been caused by an underwater evolutionary period in the history of hominids. The AAT was later picked up by Elaine Morgan, in her book, The Descent of Woman, and she has since written several other books on the subject. Morgan has also received little support from fellow scientists, but the AAT is slowly finding its way into mainstream science.

The most noticeable difference between a human and an ape is probably the differing methods of heat control the two animals have. Humans sweat, have more fat, and less fur, while other land mammals pant, are covered in fur, and do not have subcutaneous fat. First, how did we lose our fur? The savannah theory says that as humans chased after their prey, they sweated so much that their body hair became reduced. Yet, no other land predator has lost fur this way. The Aquatic Ape Theory says that humans lost their thick fur because it would impede swimming. "Oftener than not, mammals who return to the water and stay there long enough, especially in warm climates, lose their hair as a perfectly natural consequence" (Morgan 21). The hair that humans posses is not spread randomly over the body, but is instead "aligned to direct water to our midline, reducing drag" (Human Evolution). Other animals adapted to water, such as whales, dolphins, hippos, and elephants have lost significant amounts of hair.

Humans have subcutaneous fat, which means that body fat is bonded to the skin, rather than the muscles. Other primates have fat bonded to the muscles. Humans also have much more body fat than other land animals. Hardy "pointed out that the best way of keeping warm in water is to develop a layer of subcutaneous fat, analogous to the whale’s blubber, all over the surface of the body" (Morgan 24), and no other explanation for this layer of fat in humans has been found. Fat is a "characteristic of marine mammals" which "encourages buoyancy" (Watson). An aquatic human ancestor would have developed this layer of fat for insulation to keep warm in the cold water, and for buoyancy. An interesting point is that this could account for the development of the female breast. "A female breast is primarily fat, and fat floats, thus the child in the water could have access to the nipple at the surface" (Watson).

Another obvious trait that separates man from every other animal is his upright posture. Bipedalism, or walking on two feet, is not found among any other living primates. The classic savannah theory states that humans became upright as they left the jungle for the savannah, which allowed them to run faster. "These statement imply that a quadruped suddenly discovered he could move faster on two legs than on four. Try to imagine any other quadruped discovering that-a cat? a dog? a horse?-and you’ll see that it’s completely nonsensical" (Morgan 6). This actually doesn’t make much sense. "Bipedalism on the grasslands would have slowed the species down, as species that run on four legs are much faster than species that run on two" (Watson). Quadrupedal animals, like baboons and geladas, are better adapted to the savannah than humans, "if the acquisitions of modern technology are not taken into consideration" (Bender).

Most scientists consider bipedalism to be what separates man from apes, but did it evolve on the plains? The AAT suggests that early humans may have begun walking upright because of a wet environment rather than a dry one. The only theory that seems to fit is the idea "that bipedalism was first resorted to under duress, by a group of primates confronted by the necessity of wading through water" (Morgan "Rise and Fall"). Bipedalism makes humans better suited to wading, diving, and swimming. It could have been necessary for keeping man’s head above water when swimming and coming up for air (Human Evolution). This divergence between man and ape can only be explained by the Aquatic Ape Theory (Bender).

Breathing is another major area in which humans differ from apes but are similar to aquatic mammals. These factors are why humans were able to develop complex speech. "Humans are the only terrestrial animals that can voluntarily hold their breath at will" (Human Evolution - the Aquatic Ape Hypothesis). The ability to hold and control breath is necessary for complex speech (Watson). This ability would, of course, also be needed for diving. It is likely that the ability of humans and aquatic mammals to hold their breath was an adaptation meant for diving, and that the development of complex speech was a side effect.

Also, humans have a descended larynx, which other apes do not. This allows us to gulp large amounts of air (Human Evolution). Most animals only breathe through the nose, but the descended larynx allows humans to breather through our mouths, which allowed us to take deep breaths "prior to diving" (Watson). The larynx thus allowed early humans to spend longer periods of time underwater than they could have if they were taking shallow breaths through their noses. Complex speech is also dependent on the descended larynx. Other aquatic mammals, such as sea lions, walruses, and manatees have descended larynxes.

There is another similarity between humans and aquatic mammals: the diving reflex, also known as bradycardia, a decrease in heart rate and redistribution of blood to the brain and the organs. This is a natural reaction of humans to being submerged. Other apes do not share this ability, as they obviously have no use for it. "Humans can dive to depths of one hundred meters at the extreme but most humans can certainly dive to ten meters," which no ape would do (Watson). The diving reflex makes swimming and diving practical, and humans have no living ancestors that possess this trait. It must have been acquired at some point after humans split from apes, and this supports the idea that man evolved in an aquatic or semi-aquatic environment.

The Aquatic Ape Theory is at least a reasonable hypothesis, if not a fully acceptable scientific theory. It provides a sensible explanation for why human beings, while genetically similar to apes, possess so many different physical features, and how these physical adaptations could have come into being. Without the Aquatic Ape Theory, it is hard to explain the parallels between humans and aquatic mammals. Science, especially evolutionary biology, is a constantly changing field. Nothing is set in stone. The AAT may someday replace the savannah theory of human evolution, or perhaps a third theory will arise. At the very least, Elaine Morgan’s books have made some scientists rethink what they have been taught about evolution.

Bibliography

Bender, R, M. Verhaegen, and N. Oser. "Acquisition of human bipedal gait from the viewpoint of the aquatic ape theory."
http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?CMD=Display&DB=PubMed (5 June 2002)

Douglas, Kate. "Taking the Plunge."
http://www.cise.ufl.edu/~nantonio/aquatic_ape_theory.htm (5 June 2002)

Morgan, Elaine. The Descent of Woman. New York: Stein and Day, 1974.

Morgan, Elaine. "The Rise and Fall of the Savannah Theory." ReVision Fall 1995:
Vol. 18, Issue 2, p4, 4p.

Watson, Paul. "Against the Current."
http://www.oceanrealm.net/winter01/watson.html (5 June 2002)

"Human Evolution - the Aquatic Ape Hypothesis"
http://www.bbc.co.uk/dna/h2g2/alabaster/A730531 (5 June 2002)

The links may be obsolete by now. This was written for 10th grade biology.

The Savanna Theory

In the 90s a much loved theory about human evolution began to crumble quietly in the halls of science. Unlike when the fall of a scientific hypothesis is often caused by a better hypothesis, in this case there was only a vacuum to replace the Savanna theory. The issue in question was one of selective pressure; why and how humans evolved certain unique characteristics not shared by other primates.

  1. Why does homo sapiens walk on two legs?
  2. Why did he learn to speak?
  3. Why has he lost his fur?

This seldom questioned theory, though flimsy, has as its crux that man began to walk upright once he migrated from the trees to the open savanna. The height gained from bipedalism aided hunting, avoiding predators, with the side-effect being hands that loitered ineffectually at the side. Thankfully, instead of vestigial drumsticks like the T-Rex or a jump down the evolutionary ladder from homo sapiens to homo autoeroticus-constans, we instead picked up a freaking stone axe. We were the new badass stone age-lumberjacks on the scene, deal with it! Oh, and there was supposedly a bit of art and music somewhere in there too.


In a clear chicken or the egg scenario, the process of doing these new creative activities effected intelligence in the brain, which may have given rise to the ability to speak. But then, how did we do these new creative activities without the necessary intelligence in the first place? Let us pause for a second to scratch our collective chin. "Hmmm..."


As for the new "always naked" apes on the African scene, Savanna doesn't have much to offer in the way of an explanation. The larger problem with the Savanna theory is that it makes sweeping assumptions about humanity based upon a small subset of data from an isolated geography.


The whole "Head to grasslands, young ape-man" theory arose during a time when human fossils found in South Africa near grasslands were in the limelight. Anthropologists have of course made many other finds of even older humans living in wooded, wet areas bipedally. The famous Lucy was actually buried next to a lake.


A less well-known theory also exists that offers a different selective pressure as cause to bipedalism, speech, and hairlessness. Instead of the grasslands as trait incubator, humanity's ancestors go back instead to the water from which each mammal was born.


Tenets of the Aquatic Ape Hypothesis

  • Every mammal that has become naked and hairless has an aquatic ancestor, even the Rhinoceros and Elephant. The one exception is the Naked Mole Rat, that lives its life entirely underground.
  • Bipedalism. All primates have the ability to walk on two legs for a short time, but when they wade through the water they always walk upright. This phenomenon was noted by David Attenborough as well, a supporter of the Aquatic Ape hypothesis.
  • Unlike all other primates, human have a subcutaneous fat layer (especially prominent in infants). Other aquatic mammals, such as the whale, possess this same type of fat layer.
  • It is no shape in the way the throat is formed, or particular set of muscles in the tongue that the lesser primates possess that prevents speech. It is not even intelligence - the gorilla cannot even mimic the sounds of human speech. Why? The key difference lies in the ability to fine-tune the flow of fuel into the engine, breath through the vocal chords, that is unseen among non-human land mammals. The only creatures with this ability are diving animals and birds.

Of course, as with most discussions about the exact cause of a unique evolutionary trait gained hundreds of thousands to millions of years ago, the evidence does not prove causality. We have plenty of physical evidence to support something less unique, such as the return of some land-based mammals to the ocean. The unique traits of humanity, which remain the holy grail of evolutionary study, often are explained by very clever answers to "what if" questions.


Consider come counter-points to the AAH, courtesy of Wikipedia.

  • Hairlessness - most aquatic mammals that are comparably sized to humans are not hairless, but have dense, insulating fur and swim very well, with fatty layers beneath the skin.
  • Bipedalism – the disadvantages cited for bipedalism within the AAH are often the result of comparing humans to medium, terrestrial quadrupeds, but human evolution never included a period of quadrupedal locomotion.
  • Body fat – the subcutaneous fat distribution in humans is more similar to a domesticated animal than an aquatic one, and is nearly identical to that of other primates.

But then, some counter-counter-points.

  • Bipedalism out of water causes considerable problems for the back, knees and organs, while water would support the joints and torso and permit breathing.
  • A hooded nose, muscular nostril aperture control and the philtrum preventing water from entering the nostrils.
  • Vestigial webbing between the fingers

Clearly, in the battle between the Savanna and Aquatic Ape hypotheses there is no clear winner and loser. It may be that the questions that begin with Why... are so enchanting because their difficulty alone greatly increases the satisfaction that an answer brings. But of course, these issues hit so close to home that I secretly believe even the most staunch creationist feels a stirring of curiosity and wonder when news is brought to light. You know who you are, you crazy bastards! :D



The Scars of Evolution by Elaine Morgan
http://books.google.com/books?id=JkXvp0eAhAoC&printsec=frontcover

Elaine Morgan says we evolved from aquatic apes
http://www.ted.com/talks/lang/eng/elaine_morgan_says_we_evolved_from_aquatic_apes.html

At the time of this writeup, the Aquatic Ape Hypothesis has been effectively dismantled by the scientific community: most of the 'facts' used to support it are either outright false or else removed from meaningful context in such a way that they appear to contribute to the AAH, even when they support the Savanna Theory more strongly and consistently. Here I shall clarify these falsehoods and failures in academic rigour.

The Mammalian Diving Reflex is present in all mammal species, and all vertebrates have some analogue to it, even non-mammalian species.

All mammals and most vertebrates can voluntarily hold their breath, and nonhuman mammals would regularly die from inhaling their food if this was not the case, since all terrestrial mammals' respiratory tract and digestive tract use the same plumbing; this is also part of why all mammals can get hiccoughs.

Seals and whales do not hold their breath when they dive. The only oxygen they take with them on a dive is what they store in their blood; they actually expel the air from their lungs before a dive. This is why you don't hear about pinnipeds and cetaceans getting the bends. Holding your breath is not uncomfortable due to a lack of oxygen; the oxygen in your lungs is actually quite adequate for a very long span of time, if oxygen is the only concern. The discomfort of holding your breath comes from the carbon dioxide buildup in your blood, raising the pH of your blood and sending a signal to your brain that you need to exhale all of that toxic gas from your lungs. Water pressure makes this sensation even more urgent and uncomfortable. Many deep sea free-divers use lungpacking techniques like pre-dive hyperventilation to raise their blood oxygenation, and they will also exhale instead of inhaling immediately before submerging, but this method is not intuitive or instinctive, and it was arrived-at because of rigorous efforts by free-divers to find an ideal breathing technique. It takes training and practice simply to be able to hyperventilate effectively and without falling unconscious.

All mammal infants are able to float and swim at least minimally in water.

As swimming-capable species go, humans are extremely slow in water and have extremely poor endurance for distance swimming, along with having very inefficient placement of our weight along the length of our body. The same large lungs which are cited as an aquatic advantage are actually a disadvantage to efficient swimming, because they make us "top-buoyant" rather than "top-heavy" in the water. This forces our shoulders to sit much higher in the water than the forward-most body structures on any other aquatic animal, a feature that results in greater drag, lower water displacement per stroke, and significantly increased difficulty maintaining any kind of depth in totally submerged swimming.

Our lungs' size and placement is, however, very useful for long distance endurance running. Our entire physiology is ideally suited for running longer distances without rest than any other animal species can sustain, especially animals historically hunted by humans on land. The closest animals to this kind of endurance are horses and canids - animals which conveniently can also survive in most of the climates where humans can survive; it makes sense that these would be the animals domesticated and assimilated most completely into human life for so much of our species' history. It makes sense that these animals became our partners in hunting.

Most Old World Primates have downward-facing nostrils; humans are hardly unique in this feature. It is still easy to get water in a human nose, and the human nose is structured in such a way that we have a strong olfactory sense compared to other animals with binocular colour vision. Strong senses of smell are useless to mammals underwater, and no aquatic mammal has binocular colour vision. Most aquatic mammals in general have very poor vision; sea otters have much better vision above water than underwater.

All primates have salty tears. Healthy aquatic vision requires greasy tears rather than salty tears, in order to protect the eyes from oceanic saltwater (which has a harmfully different pH from human skin and eyes - something well known to anybody who has ever endured saltwater abscesses).

The "descended" larynx of humans is cited as an unique improvement of our ability to inhale deeply for diving, and part of the AAH bases lesser hypotheses around the apparent lack of descent in other apes' and terrestrial animals' larynges. Even if we are to disregard that deep inhalation is good for running and bad for diving, as was addressed earlier within this writeup, the initial assertion itself is erroneous: chimpanzees, pigs, canids, goats, genus Panthera, gallinaceous gamebirds, passerine birds, and most monkey species all have descended larynges. The other offered 'reason' for descended larynx is that it allows especially low vocalizations which would travel well in water. Low vocalizations travel well in air, too, and a majority of human vocalizations qualify as quite high compared to the vocalizations of elephants, crocodilians, and baleen whales (the three largest groups of animals known to use infrasound to communicate over long distances).

Hairlessness is an effective way to stay cool when running long distances; it is also effective for avoiding fur-inhabiting parasites, reducing the need to spend significant spans of time allopreening. Cranial hair limits sunburns to the top of the head while providing some shade for the eyes. Sea otters have some of the densest fur of any mammal; aquatic life does not automatically mean loss of fur, just as terrestrial life does not automatically mean keeping fur.

Bipedal locomotion makes us significantly taller than animals which have historically predated upon or competed with humans. The benefit of height and binocular long-distance colour vision for a terrestrial, omnivorous animal is obvious: we can see farther than the things that eat us; we can see our prey before it sees us (even-toed ungulates have notoriously poor vision compared to their other senses); we can use projectile weapons with high accuracy. On that last point, humans are among the only primates which can throw objects both far and accurately.

Subcutaneous fat deposits are a logical result of an omnivorous diet containing both fats and carbohydrates, while most other animals can only effectively digest one of those macronutrients effectively. Being able to digest carbs and fats both meant that ancient humans could survive lean hunting seasons on primarily plant diets, then survive seasons of poor vegetation by eating primarily meats and other animal-sourced foods. Hibernatory bears likewise have subcutaneous fat derived from an omnivorous diet, and they are similarly terrestrial animals who can swim but do so relatively inefficiently.

None of these statements wholly eliminate the possibility of aquatic ancestors of modern humans, but if anybody is going to attempt to prove humans are not a purely terrestrial species, they will need to produce much more convincing evidence and arguments than the attempts which have been made so far.

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