Daylight Has Helped To Shape Things Like Our Skin Color, Eye Size, Hair Texture, And Sleep Cycles
Throughout history, most human activity has been performed in daylight. Modern technology has allowed us to work and play in the dark now, but there is evidence that sunlight continues to affect our behavioral patterns and our biology.
For instance, we still sleep at night and are awake during the daytime. Furthermore, light could explain how human ancestors evolved to walk on two legs and have curly hair. Light may even have something to do with our skin color and eye size.
The first modern humans evolved in warm climates in Africa. Humans likely began to walk upright on two legs as a way to reduce exposure to the bright, harsh sunlight.
Standing up helps less sunshine hit our bodies when the sun is high overhead. Curly hair may also have provided protection from the hot sun. It acts as a thicker layer of insulation to shield the scalp than straight hair.
Additionally, strongly pigmented skin offered sun protection for early Homo sapiens. Sunlight breaks down folate, also known as vitamin B9. It speeds up aging and causes damage to DNA, but dark skin helps protect against this while still absorbing enough UV light to produce vitamin D.
But when people started moving into temperate zones with weaker light, they evolved to have lighter skin. This evolution happened relatively quickly, within the last 40,000 years or so.
Since UV radiation levels were reduced nearer the poles, less pigmentation was needed to prevent sunlight from breaking down folate. As a result, more light could be let into the body to produce vitamin D.
However, less pigmentation meant a greater susceptibility to sun damage. It’s why places like Australia have some of the world’s highest rates of skin cancer.
More than 50 percent of Australians are of Anglo-Celtic descent, which means they have light skin while living in an environment with high UV light levels. It’s a recipe for sunburns.
kieferpix – stock.adobe.com – illustrative purposes only, not the actual person – pictured above a woman stands facing the sun in a field
Sunlight has also played a role in shaping human eyes. Humans from high latitudes have less protective pigments in their irises and larger eye sockets to let in more light.
Another part of our evolutionary background is our circadian rhythm. We still follow the same sleep-wake cycle based on light, just as our ancestors did.
Humans can see well in bright light but very poorly in dim light. Our closest relatives, gorillas, orangutans, and chimps, are active during the day and sleep at night as well. They support the idea that early humans had similar behaviors.
The lifestyle probably stretches past great apes all the way back to the dawn of primates. The earliest mammals tended to be nocturnal so they could hide from dinosaurs.
However, the meteorite impact that wiped out dinosaurs likely allowed mammals, namely primates, to evolve a lifestyle of being active during the day.
If we really did inherit this pattern from early primates, that means our circadian rhythm has been part of us for almost 66 million years.
To this day, light continues to change us. Within the past 200 years, artificial lighting has made us less dependent on daylight and removed us from our ancestral circadian rhythms.
But it has negatively impacted our eyesight in recent decades. In just 25 years, many genes associated with short-sightedness have become more common.
There’s no doubt that light will continue to shape us, yet the exact long-term effects are unknown.
Sign up for Chip Chick’s newsletter and get stories like this delivered to your inbox.
More About:News
Read This Next
