Aquatic Ape Theory: Fact or Fiction?

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aquatic ape theory
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The origin of the human species has concerned us for centuries. Religion, science and philosophy have all sought to answer a question which seems to be central to the human condition: where did we come from? Today, the most accepted school of thought is grounded in science: anthropologists, paleontologists and evolutionary biologists are the experts we turn to for answers to this difficult question. Hundreds of scientists have dedicated their careers to researching and determining where the human species came from, and how it evolved into its present form. This has given rise to numerous findings and theories regarding human evolution.

aquatic ape theory

Elaine Morgan
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However, one of the most controversial theories of human evolution comes from an unlikely source: a Welsh television writer by the name of Elaine Morgan, who has no formal training in the sciences. Frustrated by the lack of clear answers to the question of our species’ origin, Morgan adopted and popularized the formerly unheard of aquatic ape theory (aquatic ape theory). This theory proposed that humans’ ancestors lived in and next to bodies of water for about 2 – 4 million years, and that this habitat choice is the cause of many of the human species’ distinguishing features. The aquatic ape theory suggest that the main reason why we differ from gorillas, chimpanzees, and bonobos (which all share a common ancestor with us) is that humans adapted to live in aquatic environments, while apes did not.

The aquatic ape theory is highly controversial to say the least. While Morgan staunchly argues that there is a lot of evidence for the theory, most scientific experts dismiss the theory as pseudoscience and unfounded speculation (Langdon, 479). Few scientists have expressed support for the aquatic ape theory; those that do risk being ostracized and ridiculed by the scientific community at large. This essay will explore the rationale behind Morgan’s theory, and describe and assess the evidence that Morgan cites in the theory’s favor. It will then analyze the scientific community’s take on each point of evidence that Morgan presents, and conclude with a reflection on the validity and plausibility of this revolutionary theory.

The Origin of the aquatic ape theory

Human skeleton alongside a chimpanzee skeleton, our last common ancestor
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Most anthropologists agree that about 9 million years ago, a species called the Last Common Ancestor (LCM) lived in the forests of Africa. This species then evolved and branched into multiple species, which evolved and gave rise to gorillas, chimpanzees, bonobos, and humans. This is the central and most commonly accepted theory of the origin of the human species. It has been shown that we share up to 98% of our genes with these non-human primates.

This has led researchers to an obvious yet very puzzling question: why is there such a large difference between humans and the other surviving descendants of the LCM? Why are gorillas, chimpanzees, and bonobos all so similar, while also being so markedly different from humans? This is a key question which anthropologists and paleontologists have long debated and sought to answer.

Elaine Morgan states that researchers first explained the contrast between humans and other descendants of the LCM using the “Savannah Based Model.” This model suggested that as the climate changed, the ancestors of humans moved from the humid jungle to the dry savannah, which made them evolve and develop the characteristics we have today. However, this model began to be questioned when new evidence and fossils were discovered in the 1980s. Fossils with certain characteristics did not match the dates and climates in which they should have lived. By the 1990s, the Savannah based model had been rejected by most anthropologists.

Once the Savannah Based Model had been rejected, many anthropologists adapted it and made it more fluid, simple and general. However, Morgan argues that this is not an adequate replacement for what used to be a clear and well defined hypothesis (Morgan, 18). Citing a lack of explanations for the differences between humans and the other descendants of the LCM, Morgan states that an alternative theory is necessary, and thus proposes the aquatic ape theory.

Most fossils of human ancestors were discovered in the Rift Valley, which spans from Tanzania to Ethiopia. Many of these fossils were found next to a body of water. Most anthropologists suggest that this is because they died when they were searching for water. However, Morgan argues that this may have been because they lived in a water area (Morgan, 27). In fact, Morgan cites evidence from National Geographic to suggest that much of the Rift Valley was covered in water between 6 and 8 million years ago, which is when human ancestors began to develop different characteristics than the other descendants of the LCM. Morgan suggests that human ancestors were forced to live in or near the water for about 2 – 3 million years, and thus developed the unique characteristics that separated them from the other descendants of the LCM.

Evidence in Favor of the aquatic ape theory

What follows is an examination of the major pieces of evidence cited by supporters of the aquatic ape theory theory. Most of these are differences between humans and the three other descendants of the LCM which, according to aquatic ape theory proponents, can only be explained as adaptations for living in and near bodies of water.


The most obvious distinction between humans and the other LCM descendants is that humans alone are bipedal. The other three descendants are all quadrupeds. The human pelvis allows humans to walk upright comfortably, while the other LCM descendants have a pelvis that is tilted forwards, which makes it difficult for them to walk bipedally for more than small distances. Quadrupeds that become vertical need to alter their skeletal system, as well as their vascular system, to allow blood to circulate efficiently. Such significant alterations must have happened for a clear reason. The aquatic ape theory suggests that human ancestors became bipedal when they started to live near the water, since this allowed them to easily stay in the water while maintaining their airways above water. This would allow them to obtain more food and move more easily through shallow areas of the water.


A Somalian Naked Mole Rat. Image Source

A second important distinction between humans and the other descendants of the LCM is that humans are hairless, while the other descendants have fur. With only two exceptions, all hairless mammals are aquatic to some degree. The first exception is humans, and the second is the Somalian Naked Mole Rat. This animal lives below ground, and never ventures above ground by its own will. All other furless mammals either live in the water (seals, dolphins, wales) or have an aquatic evolutionary history (such as pigs and hippopotamuses). Morgan notes that small aquatic mammals use fur conserve heat (such as the otter), while those aquatic mammals that are the same size as a human, or larger, are naked and use fat to conserve heat. This suggests that when human ancestors began to live in water, they shed their hair to avoid drag and used fat for insulation (which is more efficient for staying warm). Given the evidence of other species’ habitats and their hair or hairlessness, it would make sense to assume that humans shed their hard when the entered the water. (Morgan, 71 – 86)

Body Fat Percentages

Humans have much more fat in their bodies than do other primates. In men, body fat percentages range from 18 – 24%, while women have 25 – 31% body fat. Human women cease to menstruate if their body fat is below 17% (Morgan, 88). Yet most primates are healthy and fit if they have a body fat of around 2%. Layers of fat are used to keep the body warm. Human ancestors essentially replaced their former mode of thermal protection (hair) with a more efficient system (fat). Having a high body fat percentage has numerous drawbacks, such as loss of speed due to extra weight (Morgan, 89).  Morgan argues that if human ancestors were living on land, the disadvantages to having a large amount of fat would outweigh the benefits. The thermoregulatory benefits of fat would only outweigh the disadvantages if an animal is living in water, where heat loss occurs far more quickly. Therefore, Morgan suggests that human ancestors developed this characteristic when they lived in and around the water.

Breath Control

In all invertebrates, the breath is controlled automatically. In all mammals, the urge to breathe is initiated when the brain detects rising levels of carbon dioxide in the blood. In non-human primates, including the three non-human descendants of the LCM, consciously regulating the breathing cycle is impossible. Bonobos, gorillas, and chimpanzees cannot hold their breath: when carbon dioxide levels reach a certain threshold, the brain automatically triggers an inspiration. Humans, on the other hand, can consciously regulate and control their breathing cycles, and some have succeeded in holding their breath for up to nearly 12 minutes. It would only be logical for this stark difference between humans and the three other descendants of the LCM to have a clear reason. If human ancestors lived in and near the water, and gathered food in the water, having conscious control over the breath has obvious benefits.

A freediver holds her breath and freedives down to an elephant at -20 meters in Dahab, Egypt.

These differences between humans and the other LCM descendants are the ones that offer the most compelling support for the aquatic ape theory. Elaine Morgan and other aquatic ape theory proponents have cited various other differences between humans and other LCM descendants that may support the aquatic ape theory theory, such as the presence of salt glands, skin thickness, and mating postures.

Evidence Against the aquatic ape theory

There is no shortage of evidence against the aquatic ape theory. In fact, scientists have numerous theories about the origin of every difference between humans and LCM descendants. In other words, evolutionary experts have proposed many of explanations for these differences, and nearly all of them suggest that the differences did not arise because human ancestors began to live near or in the water.


Scientists have proposed numerous other reasons why humans evolved to be bipedal. These include being able to use the hands for tools, such as spears for hunting, energy conservation, long distance running, as well as being able to use the arms for carrying infants. McHenry argues that these benefits outweigh the disadvantages of being bipedal, and suggests that humans likely became bipedal for these specific reasons. This makes it seem less likely that humans would only benefit from bipedalism in the water.


While Morgan suggests that hairlessness allows humans to move more efficiently in water, critics of the aquatic ape theory theory have argued that the benefit from this is minimal. Mammals that that are highly hydrodynamic, such as dolphins and whales, would obviously be slowed down considerably if they had fur. Humans, though, are not as hydrodynamic as whales and dolphins, so the lack of fur isn’t as great a benefit. If humans had adapted to move efficiently in the water, scientists argue, they would have developed a skeletal system that is more streamlined in the water (Langdon, 479 – 494; Jablonski).

Body Fat Percentages

In her analysis of body fat in humans, Morgan repeatedly relies on the research of Caroline Pond, a leading researcher on fat storage in humans and mammals (Morgan, 87 – 101). However, she does not account for some of Pond’s research which seems to suggest that there are other, non-water related reasons for the high percentage of body fat in humans. Pond suggests that humans (and other mammals) use fat mainly as a store of energy, which benefits the species during times of food scarcity. While having fat slows humans down, it’s not clear whether the amount of fat we have today is an accurate representation of the levels of body fat percentage that we had a few million years ago. Pond found that fat percentage is largely related to diet and food availability, so the current levels of body fat percentage in humans may be due to increasing availability of food in the last few millenniums, and may not be an effect of evolution that occurred millions of years ago.

Breath Control

Critics of the aquatic ape theory have pointed out that other mammals with no aquatic evolutionary history have control over their breathing cycle. For example, Lin showed that dogs have an ability to hold their breath, and that their heart rate slows down when they do so (Lin, 279). Critics of the aquatic ape theory have also pointed to the remarkable ability of seals and whales to dive for hours at a time, and suggest that if humans had indeed evolved in the water, we would have developed the ability to hold our breath for far longer than 12 minutes. More specifically, scientists have pointed out that the drop in heart rate experienced by diving mammals is much greater than the drop experienced by humans during a dive.


The vast majority of formally educated scientists strongly reject the aquatic ape theory. In fact, the theory has been popular mainly among the general public, perhaps because it is simple and easy to understand. There is a general consensus among academic scientists that the theory can be easily dismissed, and does not warrant serious analysis. Because of this, very little formal scientific research has been done on the theory.

Throughout her career, Elaine Morgan fiercely argued against the scientific status – quo, and insisted that her theory should be considered as a viable possibility. However, the scientific community has largely ignored this, and Morgan’s response was that scientists did not want to question a theory which would invalidate all of their past research. She argued that scientists who had spent their entire careers using simplified variations of the Savannah Based Model only stand to lose from a new model that suggests that all of their previous work is wrong.

However, some scientists have taken the aquatic ape theory seriously enough to offer a formal criticism. For example, Langdon published a critique of the theory in the Journal of Human Evolution in 1997. He agreed that scientists were still working out the details of how humans evolved, and that many questions remain unanswered. However, he argued that the aquatic ape theory did not provide plausible and convincing answers to these questions. He describes the aquatic ape theory as an “umbrella theory,” which means that it’s a theory that easily explains a lot of things at once. This makes it easy to understand and appealing to the general public, he argues. He also states that unlike the general public, the formally educated scientific community is aware that most accepted explanations of evolution are highly complex, and are centered around a mosaic where human evolution happened over millions of years in a varied habitat. This is difficult for the general public to understand. When they are presented with a simple and appealing explanation, such as the aquatic ape theory, the public quickly embraces it.

Another common critique of the aquatic ape theory is that it cherry picks the evidence. Upon close analysis, it becomes clear that aquatic ape theory is not as simple as the general public likes to believe. There are dozens of adaptations that would clearly have been beneficial to human ancestors if they lived in the water, but that humans do not have. For instance, aside from having a pelvis that is vertically oriented, the human skeletal system has is not adapted for hydrodynamic streamlining in the water. The breath hold capabilities of humans are nowhere near those of diving mammals such as the seal, and our arms and legs are far less efficient for propulsion in the water than the broad appendages that water mammals such as the beaver and dolphins have.

Elaine Morgan counters this argument with the statement that humans were only in the water for 2 – 3 million years, which is a very short time from an evolutionary standpoint. Whales and dolphins have been aquatic for almost 70 million years, which was enough time for them to develop significant adaptations for living in the water. Morgan states that we did not get fully adapted to the water because we spent so little time living in a water environment (Morgan, 31). However, mainstream scientists are right that these problems show that the aquatic ape theory is far more complicated than is proponents make it out to be. It seems like whenever scientists propose an adaptation that would have suited humans living in the water, and that we do not currently have, aquatic ape theory proponents simply state that we didn’t have enough time to develop this feature. This is a very convenient argument, since it allows aquatic ape theory proponents to easily dismiss any evidence against the theory. 


Without formal training in anthropology, paleontology, nor evolutionary biology, it is difficult to provide a conclusive assessment of the aquatic ape theory. It is clear that the arguments put forth by Morgan are compelling and seem to make sense. They are easy to understand, and seem to make a strong case for the theory. However, the scientific community seems to have a valid counter-explanation for every individual piece of evidence that aquatic ape theory proponents have brought forth. The only shortcoming of these counter-explanations for human features is that they cannot be aggregated and summed up into a cohesive narrative or theory. This is the reason why the public finds the aquatic ape theory so appealing: it is simple and provides a nice, clean story that accounts for many the features humans have today. However, only further research, both on the aquatic ape theory and the scientific community’s counter explanations, can bring to light how humans truly became the species that we are today.

Researchers have recently begun to question whether the urge to breathe is truly triggered by rising levels of carbon dioxide (in humans). Some scientists have proposed that this is regulated by insulin levels rather than carbon dioxide levels. However, the prevailing and most commonly accepted evidence still suggests that the urge to breathe is regulated by carbon dioxide levels in the blood.

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