Buzz
Why do humans today look so remarkably different from apes when various ape species appear relatively similar to each other?
Fifty years ago, the prevailing scientific belief was that our ancestors transitioned from living in trees to hunting on the savanna. However, fossil discoveries later challenged this narrative. In the Great Rift Valley, where early hominids thrived, paleontologists found that the associated microfauna, pollen, and vegetation from that era were not savanna species.
The picture of early humans hunting on a golden savanna made for striking imagery in biology textbooks. However, the truth is that we became bipedal before the savanna ever existed. This classic image also failed to explain other key aspects, such as the emergence of our large, complex brains.
Once regarded as a fringe theory, the notion that humans evolved near water and possibly led a more aquatic lifestyle has gained increasing support within the scientific community. Even the renowned natural historian Sir David Attenborough has remarked, “It isn’t yet the hypothesis that most students are taught, but perhaps its time has come.”
Once referred to as the “aquatic ape theory,” it has now been rebranded as the “waterside model,” likely to sound less outlandish. No one claims our ancestors were mermaids swimming with whales or conversing with crabs. Rather, as Elaine Morgan, an advocate of the theory, puts it, “The difference between man and apes has something to do with water.”
Here are a few compelling reasons to reconsider the aquatic ape theory and its potential validity.
10. Larger Brain
The anatomy of the human brain is distinctly different from that of an ape, particularly in the cerebral cortex. Ours is significantly larger (even though it may not always appear so). The traits that set us apart—such as our ability to use language, create tools, and develop fine motor skills—are a result of this crucial advantage. The real question is: How did our brains evolve to serve these unique purposes?
The expansion of the human brain can be compared to that of seals and dolphins. It seems that marine diets are the only ones capable of supporting brain growth, as they are rich in “brain-specific” polyunsaturated fats like docosahexaenoic acid (DHA), an omega-3 fatty acid.
Savanna hunters' land-based diet simply doesn’t provide the nutrients required for such a drastic change to happen. No primate can develop a large brain with just land-based food. In fact, as animals grow larger on land, their brains tend to shrink. Consider the horse, with its walnut-sized brain.
In contrast, the opposite happens in the sea. Dolphins, for example, possess a brain weighing 1.8 kilograms (4 lb) because seafood provides the nutrients necessary to promote brain growth. This explains why dolphins have larger brains than zebras despite their similar body sizes. Interestingly, the sperm whale has the largest brain in the world, weighing 7–8 kilograms (15–18 lb).
9. Enlarged Sinuses
Our noses are among the most peculiar in the animal kingdom. These uniquely shaped snouts are not shared by any other member of the ape family, nor by any other land mammal. We possess remarkably large sinuses, which are the hollow spaces in the skull between the cheeks, nose, and forehead. They seem to have no clear function—unless you consider the possibility of an aquatic adaptation.
If we consider an aquatic ancestry, it seems that our design serves a highly functional purpose. These empty air cavities could function as buoyancy aids, helping to keep our heads above water. They also serve to protect the upper airway in a watery environment.
Have you ever wondered why our nostrils are tilted at such a peculiar downward angle? It certainly seems to help keep water out of our nose when swimming, doesn’t it?
Our sense of smell, however, is not particularly keen. Remember, underwater, a sharp sense of smell isn't necessary. For instance, diving mammals often have a diminished sense of smell. It’s just a hint of a trail, but you might be catching a faint whiff.
8. The Shift to Bipedalism
Humans have been walking on two legs for approximately two million years. (Some sources claim four million, and others say six million. In any case, it's been a significant amount of time.)
At one point, it was believed that the shift from life in the trees to survival on open grasslands was the reason for this change. However, when baboons left the jungle and entered the savanna, they remained firmly on four legs.
Why is that? If walking upright for extended periods offers advantages, why didn’t more species evolve to adopt this trait?
Walking on four legs is clearly more efficient when it comes to balance and speed. Of course, we now know that the savanna didn’t even exist back then. It turns out that baboons do stand upright occasionally, but only for a very specific purpose—to wade through water in search of food!
David Attenborough shared that throughout his long career, he witnessed various primate species wading bipedally through water, crossing shallow rivers and pools. But once they reached land, they immediately dropped to all fours again. Wading through water is the only situation in which these primates will walk on two legs.
Humans only manage to walk efficiently due to our extended legs and vertical hips. But even so, it feels somewhat awkward. It’s as if we’re falling forward in a stylish manner. So how did we come to master this ability?
Research has observed humans walking in water compared to on land, suggesting that this might be how our early ancestors developed the ability to walk. Water's natural buoyancy makes upright walking easier. The evolution of our long legs and unique walking style was driven by a strong need to adapt to these traits.
7. A Subcutaneous Fat Layer
When human babies are born, they appear as little cherubs, with chubby cheeks and adorable rolls of fat. This is because their bodies are naturally covered in a relatively thick layer of fat. Other primates, however, are not born so plump. They typically look like wrinkled, malnourished balls of skin. So, what’s the reason for this?
Beneath our skin lies a fat layer that nearly covers our entire body. This is one of the main reasons humans are capable of becoming morbidly obese, something that other primates can't do. No other primates possess these subcutaneous fat layers. Lucky us.
Interestingly, this fat layer is also found in marine mammals such as whales, seals, walruses, and manatees. This blubber serves to provide buoyancy and insulate the body, maintaining heat in cold waters. Additionally, the fat streamlines the body, making swimming more efficient. It offers a significant advantage in aquatic environments, as heat loss occurs much faster in water than in air. It’s not just comfortable, it’s vital.
6. Curiosities From Birth
When human babies are submerged in water, they instinctively hold their breath and open their eyes. This reflex, known as the bradycardic response, is a fascinating survival mechanism. If placed in cold water, their little hearts will slow down as the blood flow shifts from the limbs to preserve oxygen.
This reflex helps preserve oxygen for the brain and heart. It's not rocket science to conclude that a particularly chubby baby who instinctively holds their breath underwater didn’t evolve on the African savanna.
When infants are born, they are covered in a cheesy-like mucous layer. This slippery coating, called vernix caseosa, helps protect them from the cold. It was once thought to be unique to humans, until a team of researchers from Cornell discovered that newborn seals—pups—are also born in this slimy, greasy coating of vernix caseosa.
It’s now proposed that this physiological trait may be common to all marine mammals.
5. Sweat And Tears
Living near salty water often requires the body to expel salt. While sweating serves as an effective cooling mechanism, it’s not always necessary when one is near water and can simply take a dip. This is where tears become beneficial.
Crying helps in removing excess salt from the body. Humans sweat more than any other mammal and are the only species that sheds tears. While other mammals may cry, they don’t produce tears. Interestingly, humans expel more saltwater than any other mammal.
4. Breath Control
The reason gorillas cannot speak has nothing to do with their teeth, tongues, lungs, or vocal cords. The real reason we can speak is that we have developed conscious control over our breath, and that’s the key to speech.
All diving mammals hold their breath to prevent water from entering their lungs and to regulate the pressure in their respiratory tract as they dive, feed underwater, and surface. This refined ability to manage airway entrances was a crucial step toward the evolution of speech. Living in an aquatic environment may explain why we urgently needed to develop breath control.
In our respiratory system, we have a unique feature compared to other primates: a soft palate that can lift to block off the nasopharynx. This function is vital for aquatic mammals to keep water out of their respiratory passage.
Humans also have a descended larynx, meaning it sits closer to the lungs. As a human baby grows, the larynx lowers. Seals, sea lions, walruses, and dugongs all share this trait. And we, the only primates with this feature, can take in large volumes of air with ease.
Some researchers believe our upright posture naturally caused the larynx to descend, while others argue it was a selective pressure. The next time you hold your breath before a swim, think about how this seemingly minor trait may have been one of the most significant factors in our evolutionary journey.
3. Nakedness
We are the only primates with smooth skin. This nudity gives us an advantage in water, allowing us to glide through it effortlessly. But if that’s the case, why do we still have hair on our heads?
One theory is that hair remained on our heads as protection from sun radiation. Hair shields the scalp, and our shoulders and upper arms also have more hair. The remaining hair is arranged diagonally, pointing toward the center of the body, which reduces resistance when swimming.
A link between hairlessness and aquatic environments exists in mammals. Species that have lost most or all of their body hair, like hippos, dolphins, and manatees, are aquatic. While the elephant might seem like an example of a land mammal with no hair, it too has an aquatic ancestor—just like all hairless pachyderms, including rhinos.
It appears that every hairless mammal has some connection to water in its evolutionary history. So, why wouldn’t we?
2. Pruney Fingers
Ever wondered why our fingers wrinkle after being submerged in water for a while? This is an active process controlled by our autonomic nervous system. Evolutionary neurobiologist Mark Changizi proposes that this may have had an important purpose in our distant evolutionary past.
Changizi suggests that the wrinkled pattern might have enhanced our ability to grip underwater objects. A team from Newcastle University found some evidence supporting this theory, showing that people can grab wet marbles faster with pruney fingers than with dry ones.
This benefit only applies to wet marbles. When the marbles were dry, both pruney and dry fingers had the same grip strength. Evolutionary biologist Tom Smulders remarked, “We have shown that wrinkled fingers provide a better grip in wet conditions—it could be working like treads on your car tires, allowing more surface area to make contact with the road and [give] you a better grip.”
He suggests that this ability may have been crucial for our ancestors in foraging for food from aquatic environments.
1. Fossils And Observation Of Behavior
The fossil of Lucy, one of the earliest hominins known for walking upright, along with other notable ancestors, was found near the shores of large lakes, areas frequently subject to flooding. An examination of 20 hominid fossil sites across East and South Africa suggests that our early ancestors lived either on the edges of lakes or in flood-prone grasslands.
How did they cope with these frequent inundations?
Researchers have found clues by observing baboons in the flooded Okavango Delta during the summer. When fruit becomes scarce, the baboons turn to water lily roots as an alternative food source.
Fossil evidence reveals that early hominids also relied on aquatic plants, such as water lily nuts. These nuts, which require diving up to 5-7 meters (16-23 feet) to collect, are then roasted over a fire where they pop open like popcorn. Even today, people continue to gather and eat water lily nuts in this way.
It’s clear that our ancestors were eating seafood around two million years ago. For example, fossilized bones of a 2-meter (7-foot) long catfish, cut with stone tools, have been found. This suggests that early humans followed coastlines before venturing inland. Water was their familiar territory.
