As people that rely on the sun for so much and spend much of the day in it, why haven’t we developed an immunity to sun related issues such as burns, cancers, etc.. ?
It’s amusing that our greatest source of life is also our deadliest enemy if we are exposed for too long
In: Biology
Simply put, the sun (and all stars) are so dangerous that it is a wonder how there is any life at all. Our skin is remarkably strong to do what it does, in the first place, with only some gasses and electromagnetic waves to disrupt the guaranteed death our giant fiery sky-ball is constantly throwing at is.
Skin is a compromise. Fair skin allows you to make more vitamin D, but it can be easily damaged. Dark skin protects you from damage, but vitamin D is an essential nutrient that has few natural sources.
Our skins do a great job, as far as natural selection is concerned. We survive, generally, long enough to reproduce.
Unfortunately, there’s no easy way for nature to select for longevity in ultraviolet radiation after we get to the point that we’re able to easily reproduce.
We have developed immunity–based on where our ancestors evolved. So if our ancestors evolved in a very sunny place, people evolved to have dark skin that helps to prevent many problems of sun exposure. When some of those people moved to live in places with less sun, they encountered a problem with their adaptation to the sun, which is that they weren’t getting enough vitamin D from the sun. So people who evolved in lower sun exposure places developed lighter skin, and because they had less sun exposure in general, the problems that it causes–skin cancer, burns, etc.–were very low.
Then, the industrial age and the age of exploration came along and people started traveling all over the world and so people whose ancestors evolved in low sun places began to live in high sun exposure places and skin cancers and sun burns became a more serious problem. And people from high sun exposure places moved to lower sun exposure places and started to have problems like rickets from low sun exposure.
The sun exposure problems have been worsened by the partial destruction of the ozone layer in the past 50 years due to the use of chlorofluorocarbons. The ozone layer has a protective effect on people by blocking some of the sun’s rays. The ozone layer got quite thin at the poles, and people who were nearest the south pole suffer the most, with skin cancer rates skyrocketing in places like New Zealand and southern Australia, where most people are of European ancestry and are very pale. Even the *sheep* in New Zealand started getting lots of skin cancers. Fortunately they figured out what was causing ozone layer destruction and removed chlorofluorocarbons from use, and now the hole is mending. Though the president of the US wants to bring back chlorofluorocarbons, so we’ll see if he does so.
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