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Nina G. Jablonski, Penn State
(THE CONVERSATION) The human being has a conflictive relationship with the sun. People love the sun, but then it gets hot. The sweat enters your eyes. Then there are all the protection rituals: the sunscreen, the hats, the sunglasses. If you spend too much time outdoors or haven’t taken enough precautions, your skin lets us know with a burn of rage. First the heat, then the pain, then the regret.
Were people always 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 it wasn’t necessary. For eons, the skin resisted the sun.
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. Homo sapiens spent most of our prehistory and history outdoors, mostly naked. The skin was the main interface between the bodies of our ancestors and the world.
Human skin adapted to the conditions in which it found itself. People sought shelter, when they could find it, in caves and rock shelters, and got quite good at making portable shelters out of 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.
During a person’s life, the skin responds in many ways to routine sun exposure. The top layer of skin, the epidermis, thickens as more layers of cells are added. For most people, the skin gradually darkens as specialized cells go into action to produce a protective pigment called eumelanin.
This remarkable molecule absorbs most visible light, causing it to appear very dark brown, almost black. Eumelanin also absorbs harmful ultraviolet radiation. Depending on their genetics, people produce different amounts of eumelanin. Some have a lot and are able to produce much 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 has shown that people’s skin color in prehistory was adjusted to local environmental conditions, primarily local ultraviolet light levels. People who lived under strong ultraviolet light, such as that found near the equator, year after year had highly tanned, darkly pigmented skin capable of producing large amounts of eumelanin. People living under weaker, seasonal UV levels, such as those found in much of northern Europe and northern Asia, had lighter skin that had only a limited ability to produce protective pigment.
With only their feet to carry them, our distant ancestors didn’t move much during their lifetimes. Their skin adapted to subtle seasonal changes in sunlight and UV conditions by producing more eumelanin and darkening in the summer and then losing some pigment in the fall and winter when the sun wasn’t as strong. Even for people with lightly pigmented skin, painful sunburns would have been extremely rare because there was never a sudden shock from heavy sun exposure. Rather, as the sun grew stronger during the spring, the top layer of his skin would have gradually become thicker over weeks and months of sun exposure.
This is not to say that the skin was undamaged by today’s standards: dermatologists would be horrified by the leathery, wrinkled appearance of our ancestors’ sun-exposed skin. Skin color, like sun levels, changed with the seasons, and skin quickly showed its age. This is still the case for people living traditional lives, mostly outdoors, in many parts of the world.
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 cause skin cancer, but rarely of the variety (melanoma) that would cause death during reproductive years.
The inner life changed skin
Until about 10,000 years ago, a drop in the bucket of evolutionary history, humans made a living by gathering food, hunting, and fishing. Humanity’s relationship with the sun and sunlight changed a lot after people began to settle and live in permanent settlements. Agriculture and food storage were associated with the development of immovable buildings. Around the year 6000 a. C., many people around the world spent more time in walled settlements and more time indoors.
While most people still spent most of their time outside, some stayed inside if they could. Many of them began to protect themselves from the sun when they went out. At least in the year 3000 a. C., an entire sun protection industry grew to create equipment of all kinds – sunshades, umbrellas, hats, tents, and clothing – that would protect people from the discomfort and inevitable skin darkening associated with prolonged exposure to the sun. sun. While some of these were originally reserved for the nobility, such as parasols and parasols from ancient Egypt and China, these luxury items began to be made and used more widely.
In some places, people even developed protective pastes made from minerals and plant residues, early versions of modern sunscreens, to protect 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 were considered privileged, and their lighter skin advertised their status. A “farmer’s tan” was not glamorous: sun-darkened skin was a penalty associated with hard work outdoors, not the badge of a leisurely vacation. From Britain to China, Japan, and India, tanned skin became associated with a life of hard work.
As people have moved faster and faster over longer distances in recent centuries and spend more time indoors, their skin has not adapted to their locations and lifestyles. It is likely that your eumelanin levels are not perfectly adapted to the solar conditions where you live and therefore cannot protect you in the same way that they did for your ancestors.
Even if you have natural dark pigmentation or are capable of tanning, everyone is susceptible to damage from bouts of sun exposure, especially after long breaks completely out of the sun. The “vacation effect” of sudden exposure to strong UV rays is really bad because a sunburn indicates skin damage that is never fully repaired. It’s like bad debt showing up as precancerous or prematurely aging 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 the sign of the damage itself.
People may love the sun, but we are not our ancestors. Humanity’s relationship with the sun has changed, and this means changing your behavior to save your skin.
This article is republished from The Conversation under a Creative Commons license. Read the original article here: https://theconversation.com/human-skin-stood-up-better-to-the-sun-before-there-were-sunscreens-and-parasols-an-anthropologist-explains-why- 187559.
