Compelling Arguments Against the Controversial Aquatic Ape Theory

Argument against aquatic ape theory
Humans have evolved, over the course of several decades, from ancestors who were ape-like. Despite this, it is unclear that if they did evolve from apes, then why don't they have more common characteristics? Various theories have been formulated to explain this unique predicament, but none are more controversial and highly contested than the aquatic ape theory.
The aquatic ape hypothesis was put forth by Sir Alister Hardy, a British marine biologist, who was inspired by the observation of a parallel between the subcutaneous layers of fat (blubber) in whales and in humans.
Currently, the scientific community believes that humans evolved and developed unique characteristics, unlike those of their ape-like ancestors, as a result of adaptations. These adaptations occurred as a result of the humans choosing to live in a terrestrial environment, as compared to their previous arboreal environment. What remains contested is the fact that despite the evolution from apes, physically, humans and apes show a wide range of differences. In order to explain these diversification in body and structure, various theories have been suggested, of which only three have gained any sort of popularity.

The first theory is the aquatic ape theory (AAT) that proposes that the physical difference is due to the possibility that our ancestors lived a semi-aquatic existence, which involved activities such as wading, swimming, and diving. But, this is contradicted by the more established theory that claims that the physical differences are a result of the evolutionary adaptations of the human ancestors to the savannas of the Rift Valley. However, recent scientific studies have indicated that the climate of modern-day savannas differs tremendously from the climate present in the same location during the time of our evolution. Hence, these theories have been trumped by the recent hypothesis these differentiating adaptations were a result of the rapidly changing environmental conditions - from wet to dry, from hot to cold, and vice versa. Despite all this, some scientists still debate the aquatic ape theory, where some brush it off as being pseudoscience or fringe science, while others defend it claiming it to be the gospel truth.
Aquatic Ape Theory And Arguments Against It
Explanation - According to AAT, the transition from quadrupedalism (locomotion using four limbs) to bipedalism (locomotion using two rear limbs) was made easier by an aquatic lifestyle due to the fact that quadruped animals move on two legs while wading through water, and also because water provides a supporting buoyant effect.
Argument - There is evidence that proves that humans evolved from being quadrupeds to conducting motion via brachiation (swinging by arms from branch to branch). The progression from such an arboreal locomotion to bipedalism is quite natural.
Hairless Skin
Explanation - The theory suggests that, since water would protect the body from the sun (while swimming), the functionality of the hair was lost, and hence they evolved as relatively hairless organisms. This is with the exception of the head, as the head needs to be covered with hair since it would have been the only body part exposed to the sun. Also, loss of hair would make the body streamlined, making it easier to swim.
Argument - Hair was a defense mechanism of the body to be safe against parasites. The considerable reduction in the parasite load lead to the reduction of body hair, and this reduction was enhanced and maintained by sexual selection of hairless individuals.
Subcutaneous Fat
Explanation - The fat layers in humans resemble those found in case of whales and seals, but differ from the ones found in primates.

Argument - The fat distribution in humans is very similar to that found in domesticated animals due to the lack of strenuous physical activities as compared to those carried out by our hunter ancestors and wild animals.
Expanded Brain Size
Explanation - The size of the brain has increased as a result of the protein-rich (omega-3 fatty acids) fish diet of the aquatic ancestors.
Argument - Changing environment produced new information rapidly, and the brain evolved and increased in size to be able to process the information. Larger brains were naturally selected since the better the individual was at processing, the better he/she was at adapting and surviving by making logical decisions while the ones with a smaller processing capacity took longer to reach the same conclusions, which obviously decreased its chances of survival.
Hooded Nose and Descended larynx
Explanation - The nose of humans closely resembles the blowhole of dolphins and whales, and the hooded nature of it would work to prevent water from entering the nostrils. The larynx is present in the throat in humans as well as in aquatic animals, whereas primates show its presence in the nasal cavity. The larynx is descended to provide the animal with the mild ability to control its breathing, a quality not observed in terrestrial organisms.
Argument - Terrestrial mammals, in fact, do show the presence of a descended larynx, e.g., red deer. The nose and larynx possess that particular structure in order to make speech possible, making vocalization of language clear. Also, the shape of the human larynx differs from that of aquatic animals such that it allows humans to control breathing; however, it predisposes them to choking.
Greasy Skin
Explanation - The abundance of grease on the skin of a newborn human baby is quite similar to the greasy skin observed in seals, and it acts as a form of insulation and waterproofing device. Since the greasy coat is lost shortly after birth, human skin possesses abundant sebaceous glands to serve the same purpose.

Argument - The sebaceous glands are not found in aquatic mammals, and hence humans could not possibly have evolved from aquatic ancestors.
Arguments Refuting the Theory
❖ Convergent evolution predicts adaptations that serve similar functions and purposes, but not similar structures. Hence, the wings of a bat, bird, and bumble bee are a result of convergent evolution as they serve the same function, but do not possess the same structure. In case of AAT, convergent evolution is used as an explanation for linking together adaptations with similar structures, which is incorrect.
❖ The anecdotal evidence provided by the theory can also be accounted for by the savannah or the climate change hypotheses, and hence surpasses the need for an aquatic or semi-aquatic ancestor.

❖ Humans lack anatomical characteristics of aquatic animals, even in vestigial forms, indicating that humans did not evolve from aquatic mammals. One such trait is the possession of concealed or internalized testes, which is obviously not the case in human males, who possess externalized testes.
❖ Even if humans did evolve from aquatic or semi-aquatic ancestors, these adaptations would be lost when humans became bipedal and terrestrial, and hence would not have been exhibited by modern humans at all.

❖ All the adaptations that the theory claims did not occur in accordance with human evolutionary timeline. According to fossil records, it has been proved that humans had a small brain and body hair for considerable amount of time after they became bipedal. This would not be possible according to AAT, which claims all these adaptations occurred during the same time period.

❖ The theory, instead of finding and accumulating supportive irrefutable evidence, has instead become a sum of various ad hoc hypotheses.
Despite the rejection of AAT by paleoanthropologists, the theory is considered as a golden example of how evolutionary theories must be falsifiable and scientifically testable.