Ancient humans didn't get sunburn.  Here's How Living Inside Has Evolved Our Skin

Ancient humans didn’t get sunburn. Here’s How Living Inside Has Evolved Our Skin

HHuman beings have a conflicted relationship with the sun. People love the sun, but then they get hot. Sweat gets into your eyes. Then there are all the protection rituals: sunscreen, hats, sunglasses. If you stay outside too long or haven’t taken enough precautions, your skin will tell us with a furious sunburn. First warmth, then pain, then remorse.

Have people always been so obsessed with what the sun would do to their bodies? As a biological anthropologist who has studied primate adaptations to the environment, I can tell you that the short answer is “no,” and they didn’t need to be. For eons, the skin resisted the sun.

The skin, between you and the world

Human beings evolved under the sun. Sunlight was a constant in people’s lives, warming them and guiding them through the days and seasons. A wise man spent most of our prehistory and history outdoors, mostly naked. The skin was the main interface between the body of our ancestors and the world.

Human skin has adapted to whatever conditions it finds itself in. People took refuge, when they could find it, in caves and rock shelters, and became quite good at making portable shelters from wood, animal skins and other gathered materials. At night, they huddled together and probably covered themselves with fur “blankets”. But during active daylight hours, people were outdoors and their mostly bare skin was what they had.

Over the course of a person’s lifetime, the skin reacts to routine sun exposure in several ways. The surface layer of the skin – the epidermis – becomes thicker by adding more layers of cells. For most people, the skin gradually darkens as specialized cells kick in to produce a protective pigment called eumelanin.

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This remarkable molecule absorbs most visible light, giving it a very dark brown, almost black appearance. Eumelanin also absorbs harmful ultraviolet rays. Depending on their genetics, people produce different amounts of eumelanin. Some have a lot and are able to produce a lot more when their skin is exposed to the sun; others have less to start with and produce less when their skin is exposed.

My research on the evolution of human skin pigmentation showed that the skin color of prehistoric people was adapted to local environmental conditions, primarily local levels of ultraviolet light. People who lived under strong UV light – like you’d find near the equator – year after year had very pigmented, very tannable skin that was able to produce a lot of eumelanin. People who lived under lower, more seasonal UV levels — such as are found in much of northern Europe and northern Asia — had lighter skin that only had abilities limited to producing protective pigments.

Having only their feet to carry them, our distant ancestors moved little during their lives. Their skin has adapted to subtle, seasonal changes in sunlight and UV conditions by producing more eumelanin and becoming darker in the summer, then losing some pigment in the fall and winter when the sun is out. wasn’t that strong. Even for people with lightly pigmented skin, painful sunburn would have been extremely rare as there was never any sudden shock from heavy sun exposure. Rather, as the sun grew stronger in the spring, the top layer of their skin would have gradually thickened over weeks and months of sun exposure.

That’s not to say the skin would have been intact by today’s standards: dermatologists would be appalled at the leathery, wrinkled appearance of the sun-exposed skin of our ancestors. Skin color, like sunshine itself, changes with the seasons and skin quickly shows its age. This is still the case for people who live in traditional ways, mostly outdoors, in many parts of the world.

Chronic exposure to the sun without protection can damage the skin, with effects that resemble those of this farmer in India. Credit: Randeep Maddoke/Wikimedia Commons, CC BY

There is no skin preserved from thousands of years ago for scientists to study, but we can infer from the effects of sun exposure on modern people that the damage was similar. Chronic sun exposure can lead to skin cancer, but rarely of the type – melanoma – that would lead to death during childbearing age.

Life inside has changed skin

Until about 10,000 years ago – a drop in the bucket in evolutionary history – human beings lived by gathering, hunting and fishing. Humanity’s relationship with the sun and sunlight changed a lot after people started settling and living in permanent settlements. Agriculture and food storage have been associated with the development of real estate buildings. Around 6000 BC. AD, many people around the world were spending more time in fortified settlements and more time indoors.

Persian King Darius the Great, who lived over 2,500 years ago, is depicted sheltering from the sun. Credit: Luisa Vallon Fumi/iStock via Getty Images Plus

While most people still spent most of their time outdoors, some stayed indoors if they could. Many of them began to protect themselves from the sun when they went out. Around 3000 BC. AD, an entire sunscreen industry developed to create equipment of all kinds – parasols, umbrellas, hats, tents and clothing – that would protect people from the discomfort and inevitable darkening of skin associated with long exposure to the sun. While some of these were originally reserved for the nobility – such as the parasols and umbrellas of ancient Egypt and China – these luxury items began to be made and used more widely.

In some places, people have even developed protective pastes made from minerals and plant residues – early versions of modern sunscreens – to protect their exposed skin. Some, like the thanaka paste used by the people of Myanmar, still persist today.

An important consequence of these practices in traditional agricultural societies was that people who spent most of their time indoors considered themselves privileged, and their lighter skin announced their status. A “farmer’s tan” was not glamorous: sun-blackened skin was a penalty associated with hard work in the outdoors, not the badge of a quiet vacation. From Britain and China to Japan and India, tanned skin has become associated with a life of hard work.

As people have moved faster and faster over longer distances over the past few centuries and spent more time indoors, their skin has not caught up to their location and way of life. Your eumelanin levels are probably not perfectly adapted to the sunlight conditions where you live and therefore are not able to protect you in the same way that they could have your ancestors.

Even if you are naturally dark-pigmented or able to tan, everyone is susceptible to damage from bouts of sun exposure, especially after long breaks spent completely out of the sun. The “holiday” effect of sudden high UV exposure is really bad because a sunburn signals damage to the skin that is never fully repaired. It’s like a bad debt that shows up as prematurely aged or precancerous skin many years later. There is no such thing as a healthy tan – a tan does not protect you from further sun damage, it is a sign of damage.

People may like the sun, but we are not our ancestors. Humanity’s relationship with the sun has changed, and that means changing your behavior to save your skin.

Nina G. Jablonski is an Evan Pugh University Professor of Anthropology at Pennsylvania State University. A biological anthropologist and paleobiologist, she studies the evolution of environmental adaptations in Old World primates, including humans. Follow Nina on Twitter @NinaJablonski1

A version of this article originally appeared on The Conversation and is republished here with permission. Check out the conversation on Twitter @ConversationUK

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