Besides having the ability of abstract and symbolic thinking, a form of intricately developed culture, and the opposable thumb, the biggest difference among us and our primate relatives is the lack of hair on our bodies.
Many would disagree with the claim we lack hair, and the waxing and hair removal industry is there to confirm this, but science shows that it is a big wonder how little hair we have.
While it is fashionable to remove much of the hair we do have, scientists dealing with human genetics and evolution pose a reverse puzzling question: why we are so hairless?
A Neanderthal male. Photo by Tim Evanson – http://www.flickr.com/photos/23165290@N00/7283199754/, CC BY-SA 2.0
There are many reasons why hair could have become unpractical along our evolutionary path. It could be to promote easier sweating and therefore temperature regulation, or it could be that we needed to communicate emotional responses through blushing or goosebumps.
Scientists are now focusing on the skin itself to find out what it takes for an area to become hairless and trying to take it from there in researching how this came about.
Comparing animals with a hairless plantar area (the wrist areas in humans) such as mice, to animals who grow hair in these regions such as rabbits scientists are trying to find out what chemical components promote or hinder hair growth.
Australopithecus afarensis. Photo by Tim Evanson; Reconstruction by John Gurche Flickr CC BY-SA 2.0
A presence of the protein inhibitor Dickkopf 2 (or Dkk2) has been noted in varying amounts across relatively hairless and furry animals.
Research on the plantar area in mice found high levels of Dkk2 in contrast to rabbits, which have exponentially low amounts of this component.
In this way, scientists concluded that Dkk2 must be directly responsible for stopping the hair growth in certain regions of the body.
Representation of Lucy (Australophitecus), Natural History Museum, Washington DC, USA. Photo by Mpinedag CC BY-SA 3.0
There are more factors interacting with Dkk2 that scientists are testing through various experiments. However, these findings alone are of extreme importance for future treatment of boldness or alopecia in humans.
With finding out one factor that affects hair growth, the big question remains: why are some parts of the body completely covered with hair and some bare. There are a couple of theories around this.
Reconstruction of a Neanderthal. Photo by Stefan Scheer – Vlastito djelo CC BY 2.5
Sarah Millar, a professor at the University of Pennsylvania’s Perelman School of Medicine, thinks that losing hair on our palms and soles of our feet is a product of evolution as hair would hinder tool management and walking barefoot, as much unwanted stuff from the ground would constantly get caught in our fur. The rest of the body is a bit harder to explain.
One theory going in and out of fashion, but not widely accepted because of the lack of scientific proof, is the aquatic ape theory.
Neanderthals
According to the aquatic ape theory, our ancestors living in the savannahs in Africa would have had to wade through water to gather food. The friction caused by hair slowed the movement down, so it was traded for fat that would keep us warm.
A more popular theory explains the loss of hair in terms of thermoregulation. Hunting during the day was done under strong sun, and humans would need a way to not overheat. Having naked skin and additional sweat glands helped in keeping us cool, while clothes substituted the fur to keep us warm when needed.
Why are humans so hairless?
Mark Changizi, who studies vision and color theories, believes that the combination of losing hair and the third cone we have in our eyes in contrast to other animals, helped humans to communicate nonverbally through detecting different hues of the skin tone.
According to Smithsonian: “A baby whose skin looks a little green or blue can indicate illness, a pink blush might indicate sexual attraction, and a face flushing with red could indicate anger, even in people with darker skin tones.
But the only way to see all of these emotional states is if humans lose their fur, especially on their faces.”
Read another story from us: DNA Study Suggests all Humans may be Descended from Just Two People
Even though the story of our millennia-long hair loss is still not completely known to us, these theories are all a good clue towards finding the truth of it. It could very well be that a combination of factors is a right answer, but the Dkk2 findings is sure to help us to solve this puzzle.