You see, pale skin is generally recognised as an adaptive feature in Euro-Asian peoples because darker skin, which evolved in Africa, filtered out too much sun to make enough vitamin D - which is made in the skin in response to sunlight and we don't normally get enough in our diets.
Let's start from the beginning:
Human beings need vitamin D for normal bone development in childhood. We can get it from two sources: from our food or by making it ourselves in our skin. Our diet is normally deficient in it so we need to supplement this by manufacturing it in our skin. This process involves ultraviolet-B (UVB) from the sun which converts a cholesterol-like substance known as provitamin D3 to vitamin D3. This is then processed further by the liver and the kidneys to form vitamin D.
Deficiency in vitamin D in childhood leads to thin limb bones deficient in calcium phosphate which give the bones strength so the child may fail to grow to a normal height, may be susceptible to bone fractures and may well have deformed limbs, especially the lower leg bones which may be 'bowed'. Teeth may also fail to develop normally. This syndrome is known as rickets and was a common developmental problem particularly in Northwestern Europe where it became especially prevalent after the Industrial Revolution in the northern industrial centres where poverty was rife, diet was poor, the climate was cloudy and the sun was weak even in summer. In the UK where rickets was a problem, the provision of free milk at school as a post-war welfare measure was largely responsible for abolishing it.
But, with UVB comes ultraviolet-A (UVA) and too much exposure to UVA can cause cells in the skin to mutate and become cancerous, giving rise to melanoma, an especially aggressive cancer. There are also a couple of other skin cancers caused by too much exposure to direct sunlight (or sunbeds). One of the reasons humans evolved dark skin as we lost body hair may well have been selective pressure caused by melanomas, in conditions where the sun was strong enough to produce enough vitamin D despite it being filtered by protective melanin in the skin.
When the immediate ancestors of modern human migrated out of Africa one of the problems preventing them extending their range northwards may well have been the incidence of rickets caused by lack of sunlight on a dark skin evolved in a part of the world where the seasons are not so well differentiated and where the sun is always high in the sky. It used to be thought that Europeans and northern Asians evolved pale skin by this selective pressure alone but it might well be that we acquired it from our Neanderthal cousins with whom there is now known to have been limited interbreeding.
Neanderthals had been evolving in Euro-Asia for some 200,000-250,000 years before Homo sapiens arrived on the scene and so had probably 'solved' many of the problems of living in colder, cloudier and more seasonal climates. In effect, we may have short-circuited evolution and acquired in a few thousand years what it had taken Neanderthals and their ancestors 250,000 years to evolve. See, So What Did The Neanderthals Ever Do For Us?
|Malignant Melanoma, European Age-Standardised Incidence Rates per 100,000 Population, by Sex, Great Britain, 1975-2011. Source: Cancer Research UK|
In countries like Australia where pale-skinned people now live their lives in strong sunlight, melanoma is a significant problem. It is now increasing rapidly in the UK since, beginning several decades ago, more people began travelling abroad to places like Spain, Greece and the Côte d'Azur to get a suntan on the beaches, or, as a fashion statement, began spending time on sunbeds to get a nice tan prior to going.
This is perfectly understandable and fully explained in general principles by a utilitarian evolutionary process which has no plan and no compassion, and fits perfectly into known human evolutionary history. It is completely inexplicable in terms of an intelligent design by a benign designer. In short, why would a compassionate designer design a problem which can only be solved by a balancing act between that problem and another one, neither of which benefit humans in any way. Did this intelligent, omniscient, omnibenevolent designer not realise his design was going to live in cloudy, northern climates and that getting enough vitamin D was going to be a problem? And did it not realise that its solution to this problem was going to cause another one?
Fortunately, science has not only explained the problem but has provided the cure - good diet and efficient sunscreening preparations. I use factor 30 because an anorak looks a bit silly on a beach and I remember all too well the blisters across my shoulders and on my shins from the second degree burns I got the first time I went abroad to bake on a Croatian beach in former Yugoslavia, 44 years ago.