- Education and Science»
- Geology & Atmospheric Science
Human Origins: Aquatic Ape Hypothesis
A Striking Resemblance
Advocating the Aquatic Ape Hypothesis
In the scientific world where the theory of evolution through natural selection is the accepted model of speciation, there are many hypotheses as to why Homo sapien is so different from other primates. There are many inferences as to what events may have caused this, all of which occur in conjunct to or after the split of the human and chimpanzee family lines. One of the widely accepted hypotheses is that the ancestors of Homo sapien, Homo erectus were a partially subterranean-dwelling species, i.e. caveman. This would account for the loss of hair, as it is seen in other subterranean species such as the naked mole rat. Another popular idea is that the ancestors of human beings evolved in a savannah environment, losing body hair because it was too warm, and becoming erect to see over the tall grass. There is also the often overlooked idea called the Aquatic Ape Hypothesis. This infers that the reason humans have different traits from other primates is because our ancestors were a partially-aquatic species. Also, taking into account the similar body features between humans and present-day aquatic mammals, the Aquatic Ape Hypothesis is a viable explanation as to why man differs so much from other primates.
Comparing humans to the other great apes, we are virtually hairless. Although hair does grows all over the body, it is nothing in comparison to the thick body hair of a chimpanzee, to which we are most closely related. But why are we so different from them? A common explanation is that Homo erectus was a cave dweller, and lost the need for hair. It can be observed that in caves, many creatures lose certain traits. The blind cave fish is a prime example of this because it has no eyes as a result of living in a dark environment. Humans may have lost their hair because it was no longer needed in a subterranean habitat, similar to the naked mole rat that lives strictly in underground burrows. Interestingly enough, naked mole rats are found in the Ethiopian lowlands, the same area in which humans are said to have evolved. Although it is a possible explanation as to why humans are hairless, this hypothesis does not account for any of the other obvious differences found between humans and the other Great Apes.
Humans losing hair due to a migration from the forest to the grassy savannah is another popular hypothesis. This idea states that Homo erectus left the forest to live in the savannah, losing hair because it was too warm, and began to walk on its hind legs to see over the tall grass. It also states that hair was kept on the head to protect the individual from the sun. The elephant, an animal living in that habitat as well, also has little body hair. Although we share similarities with this animal, we share no similarities with other savannah animals. In fact, many savannah animals such as lions, zebras, giraffes and hyenas have extensive body hair. The baboon, a fellow primate species, also has extensive body hair. Like humans, baboons are also descendents of forest-dwellers, yet humans differ so much. This hypothesis, among others, seems to be missing key components. According to Charles Darwin, “variations neither useful nor injurious would not be affected by natural selection” (Darwin 81). For natural selection to work, an individual must have a genetic trait that gives it an advantage for survival in its environment, thus giving it a reproductive advantage. This advantage ensures that the individual’s genes are passed on, along with that superior trait, for generations to come. The uselessness of body hair in a savannah environment is feasible, but it is hard to determine why a certain individual with less body hair would be more likely to survive and reproduce.
In contrast to the heat of the savannah, caves have a relatively cool atmosphere. It’s hard to see how an individual residing in a cave would have an advantage if it had no body hair in which to keep warm. Natural selection would not be able to occur in such an environment because there would be no competition for survival that would be effected by the amount of body hair an individual has. Then what happened to our body hair? Elaine Morgan proposes the Aquatic Ape Hypothesis as an answer. From her book The Aquatic Ape, she suggests “that while a coat of fur provides the best insulation for land mammals the best insulation in water is not fur, but a layer of fat” (Morgan). It is easy to see by comparing these observations to human body features, that it is indeed a possibility that human ancestry had an aquatic stage.
The Aquatic Ape Hypothesis also explains other body features that most hypotheses overlook. Homo sapien is not only unique as being the only naked primate, but also the only primate with webbed digits. This webbing is found similarly in many amphibians, such as frogs and lizards. The webbing serves as a thrusting mechanism in water which propels the creature forward, similar to a canoe paddle. These creatures have forelimbs that encompass a similar skeletal structure to that of human beings, suggesting that the range of possible movements of the forelimb is virtually identical. Given this similarity, it’s easy to see that webbing would also develop in primates if their habitat became semi-aquatic. Another feature humans share with some aquatic creatures is the nose. The human’s downward-pointing horned nose is almost identical to that of otters, and is similar in its shape to that of the area encompassing the blue whale’s blow hole. The horned shape ensures the nose will stay above water level when surfacing, making it easier to inhale. Although the otter also has body hair, it lives in a cooler environment where which hair is needed as an insulator during their time spent on land. While observing otters it is easily noticeable how quickly they dry off when on land. This is because they have sebaceous glands that produce enough oil to waterproof their hair. Humans also have these glands, whereas all the other Great Apes have vestigial sebaceous glands. This suggests that humans were exposed to an aquatic environment at one point, because active sebaceous glands would be an evolutionary advantage in such an environment. An additional similarity of human beings to aquatic animals is the amount of body fat. Human infants are born with excessive body fat. William Bond explains in his book, The Secret World of Mermaids that “newborn babies can float and swim straight away after birth. Other apes, like a newborn chimpanzee or gorilla, will quickly sink and drown, if not rescued” (Bond). The fact that infants have these characteristics suggests that it was at one point a natural thing to give birth in the water, which would also mean that human ancestors lived in an aquatic habitat for some time. Fat also works as an insulator for aquatic creatures. Elaine Morgan states that humans “have ten times as many fat cells in our bodies as would be expected in an animal of our size” (Morgan). The amount of insulating body fat on a human being can easily be explained by the Aquatic Ape Hypothesis, but is not mentioned in other hypotheses about human evolution.
Other features unique to Homo sapien can be related to an aquatic past, as well. Humans are the only living primate, or mammal for that matter, that is habitually bipedal. Curiously, another habitual biped is the penguin, which is a semi-aquatic creature. Bipedalism would not have been efficient in a savannah environment. In the savannah there are many predators, such as lions, whose food source relies on catching the slowest-running prey. With four legs, a creature is more efficient at running than with two legs. The speed in which a creature runs is crucial to survival on the savannah. An ape-like ancestor of humans would have found it more difficult to run on two legs, as its body structure was not as fully developed to suit bipedalism as it is today. It would have needed to run on all four limbs to reach a much faster speed. The missing part of the savannah theory is explaining why bipedalism would have had the evolutionary advantage.
Elaine Morgan advocates bipedalism to being a result of an aquatic environment; “if their habitat had become flooded, they would have been forced to walk on their hind legs whenever they came down to the ground in order to keep their heads above water” (Morgan). If the environment where human ancestors lived became aquatic, then they would be forced into bipedalism to go from one place to another. Evidence of bipedalism in conjunction to aquatic areas can be seen in fossil records, too. Oreopithecus bambolii (11.2 to 3.4 million years ago) was a primate that lived in the swampy regions of East Africa and Southern Europe. Its pelvic bone was structured similarly to that of modern day humans, suggesting that it may have also been a biped. Because this species lived in swampy regions, it is easy to assume that it spent a great part of its life in the water. Evidence of this kind of habitat contributing to bipedalism can also be seen today. There are two species of primates who are partially bipedal; the bonobo chimpanzee and the proboscis monkey. Their body structures permit them with the ability to easily walk on their hind limbs when needed. The proboscis monkey lives in a swampy region in Borneo, which calls for the occasional submersion in water where bipedalism is needed to travel through water while avoiding submerging the head. The bonobo chimpanzee lives in a forest region that is seasonally flooded, which would also call for submersion in the water. With this said, it can be inferred that humans at one point in their development went through an aquatic phase where bipedalism was crucial to survival. The Aquatic Ape Hypothesis explains how an individual who was efficient in walking on two hind limbs would have an evolutionary advantage over an individual who was not.
The way people act can be linked to an aquatic stage, as well. The most obvious is the ease in which people learn how to dive and swim. William Bond also mentions in his book, The Secret Lives of Mermaids that in a lot of cultures “children learn to swim before they can walk” (Bond), such as with the Yamana divers. These people dive as a means of foraging for food, and the ease in which they do so can be an indication that humans evolved to have the ability survive in an aquatic environment. Directly relating to diving are the mechanisms with which we breathe. Humans are among the only land mammals with voluntary breath control. Elaine Morgan suggests that “voluntary breath control appears to be an aquatic adaptation because, apart from ourselves, it is found only in aquatic mammals like seals and dolphins. When they decide how deep they are going to dive, they can estimate how much air they need to inhale” (Morgan). Based on this observation, voluntary breath control seems to be a feature that humans developed due to the need to forage for food underwater. The physical part of our breathing mechanism can be attributed to an aquatic exposure, as well. Humans have a descended larynx, which no other known primate or land mammal has. Morgan proposes that “this arrangement means that we can breathe through our mouths as easily as through our noses. It is probable that this is an aquatic adaptation, because a swimmer needing to gulp air quickly can inhale more of it through the mouth than through the nostrils. And we do know that the only birds which are obligatory mouth breathers are diving birds like penguins, pelicans and gannets. As for mammals, the only ones with a descended larynx, apart from ourselves, are aquatic ones - the sea lion and the dugong” (Morgan). The similarities in the breathing mechanism suggest that there is a good possibility human ancestors were semi-aquatic beings.
Another indication of an aquatic ancestor is the instinctive position in which people mate. Omitting the inventive positions stemming from human culture, people generally mate face-to-face. This is very uncommon with land animals. We mate this way because our hind limbs are directly under our pelvises, which positions the genitals in a way that makes frontal mating easiest. Elaine Morgan states that “this mode of mating is another characteristic very rare among land animals, which we share with a wide range of aquatic mammals such as dolphins, beavers and sea otters. What we have in common with them is a mode of locomotion in which the spine and the hind limbs are in a straight line, and that affects the position of the sex organs” (Morgan). She proposes that because humans and many aquatic creatures have similar genitalia placement, humans must have gone through an aquatic stage in evolution. Interestingly enough, dolphins, like humans, have sex as a recreational activity. The bonobo chimpanzees, which are seasonally exposed to a flooded environment, often mate face-to-face as well. This suggests that there was also a change in positioning of their genitalia because of the need for partial-bipedalism in the wet environment to which were and are still regularly exposed. These physical relationships between humans and other species are an indication that humans went through an aquatic phase in their evolutionary history.
The Aquatic Ape Hypothesis is a feasible explanation as to why man differs so much from other primates. Unlike other hypotheses of human evolution, it gives answers to more than just habitual bipedalism and our lack of body hair. Indicators in both fossil record and present-day observations point bipedalism to result from aquatic exposure. Lack of body hair is found predominantly in aquatic and semi-aquatic animals, as well as animals that have been linked to aquatic animals via the fossil record. Not only does this theory answer for these distinctively human traits, but it also answers for a number of other physical and behavioral traits. The physical indications of an aquatic state include webbed digits, excessive body fat, a horned nose, a descended larynx and the location of the genitalia, as well as oily skin. The behavioral similarities between humans and aquatic species are awing, because they are as minute as breathing and as significant as having sex. There are countless differences between Homo sapien and other primates, however many of these differences, both major and minor, can be explained through the Aquatic Ape Hypothesis.
"The Secret Lives of Mermaids," William Bond