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.
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.