As much as there’s a lot we don’t know about the ocean, there’s also a lot of phenomena about how our own bodies evolved that we don’t yet understand. In fact, it’s very likely that at some point in our evolution, we probably lived by the sea or in semi-aquatic habitats.

If you’re thinking about mermaids, that isn’t quite it. Take a look at your hands, then take a look at a duck or a frog’s foot.

What’s similar? Hint: look between your fingers.

What seems natural to us when we look at our hands is actually pretty uncommon in land animals. Between our fingers lies a webbing of skin, which is usually needed when living habitually in water. Webbing between fingers is something that benefits swimmers, and even sea mammals like the whales mentioned earlier have similar hand and finger bones.

Let’s take a look at some of the hands of our ancestors in our family tree. Compared to apes, we have longer thumbs in relation to our fingers and also broader palms, which is suggested to have been an “evolutionary response” because of a need for more dexterity. But is that really all there is to it? Chimpanzees, who share 98.6% of DNA with us, have great dexterity even with their thumbs, which aren’t that long. Our ancestors, who likely had longer thumbs as well as having broad hands (although our hands are much broader now). In fact, genus Australopithecus and species Homo naledi, who lived in the wetlands, didn’t use their broader hands so much for tool-use, but likely for swimming and finding floating herbs.

Did you ever swim in a pool for too long, or mellow in a bathtub full of water? If so, did you perhaps notice that the skin on your hands and feet became wrinkled and shriveled up? If anyone told you that the wrinking is from water passing through the skin and swelling it up, it isn’t!

The shriveling up comes from blood vessels constricting under your skin. The interesting thing that comes out of having wrinkled skin is that it helps us grip wet or underwater objects better. The wrinkles, assumed to “channel away” water like how rain treads water in car tires, improved the grasping of wet or underwater objects of study subjects during some experiments and tests. So, wrinkled skin possibly aided our ancestors in finding food underwater or near water, as well as improving footing in water or rain.

Our feet become another story itself. The flat shape of our feet and arched soles can be useful to swimmers and divers–they can give more thrust in swimming. If we really think about it, the flippers that divers wear are just extended feet. Since walking with flippers on land can prove to be inefficient, rather than adopting full scale flippers, we ended up with the feet shape we have now: good for swimming, good for walking. 

What about hiccups? We’ve never had any uses for those, and always try to scare them away. It could just be a remnant of living in water, as hiccups could have aided in preventing water from filling the lungs. In addition to hiccups, our noses are hooded and we also have philtrums, the grooves between our nose and mouth, which restrict water from coming into our nostrils.

Our straight-standing posture, absence of total body hair, distribution of fat, and oil-secreting glands on our skin are beneficial in semi-aquatic habitats. For instance, the straight-standing posture would normally be difficult to walk with on land, but it’s useful in water up to the thighs. If we look at our diets as well, though humans have been bipedal for five million years, humans began to eat seafood just two hundred thousand years ago.

The aquatic theory of our ancestors certainly provides some food for thought as to the way we evolved and why we evolved into how we are today. Many scientists have discovered other functions of our bodies that are suitable for wet environments, and while it isn’t concrete that we ever lived in water, our oceans and waterways have always remained a big part of our survival throughout our five million years.

And who knows? Perhaps at some point, some of our ancestors did grow mermaid tails and dive deep into the sea—after all, we still have 95% to uncover about our oceans and much to learn about ourselves.

written by Saanvi Gutta

edited by Keerthi Selvam and Evalynn Bogusz

 

References:

Verhaegen, M. (2015). Fingers, hands, feet and toes. The Aquatic HumanAncestor Theory Website. http://aquatic-human-ancestor.org/anatomy/fingers-toes-feet.html

Rhys-Evans, P. (2020, April 1). Did Human Evolution Include a Semi-Aquatic Phase? The Scientist. https://www.the-scientist.com/reading-frames/did-human-evolution-include-a-semi-aquatic-phase–67306

Bodenner, C. (2009, August 16). Aquatic Apes. The Atlantic. https://www.theatlantic.com/daily-dish/archive/2009/08/aquatic-apes/197510/

Aquatic Ape Hypothesis. Wikipedia. https://en.wikipedia.org/wiki/Aquatic_ape_hypothesis#Wading_and_bipedalism

Image Credits:

[Primate feet] [Chart]. The Aquatic HumanAncestor Theory Website. http://aquatic-human-ancestor.org/anatomy/fingers-toes-feet.html

[Animal in water] [Photograph]. Express. https://www.express.co.uk/news/science/1004845/evolution-science-apes-royal-marsden