Thread: environment and evolution hypothetical question

Hi all,

I'm a layperson, here to gather some information for curiosity only (not homework, promise!). My questions straddle several areas, some more loosely than others, so this may not be entirely appropriate place to ask. However, I thought to give it a go. Please keep in mind that this is a hypothetical scenario only:

What sort of circumstances - environmentally and evolutionarily - could have caused humans to have evolved with pure black or white skin? I mean that as in color, not ethnicity. I would appreciate as detailed a response as possible.

Hope someone is patient and kind natured enough to help a lay-bie out !

Anyone?? Awww come on! I'll dance for you via webcam! (actually that's something you really don't want to see...but hey the offer's there)

Hmmm, I dont know if there are any that would have gotten humans that far to the ends of the spectrum.

Gee, ask a tough one! This can be answered pretty well with one word. Ricketts. Ricketts is a vitamin D deficiency disease. It causes bone growth deformity. Men with Ricketts have short weak legs and cannot run rapidly. Women have deformed pelvises and die in child birth.

Vitamin D is generated in human skin by the action of that portion of sun light that has gotten past the pigment in our skin. So less pigment equals more Vit D.

We believe that the first humans evolved in Africa and had black skins. All the close human relatives(great apes) have black skins. As humans became successfull and their range expanded out of Africa they had to deal with weaker sunlight in northern latatudes and climates that required the wearing of serious clothing. Less skin exposed to weaker sunlight equals reduced vit D and increased rates of ricketts. Bingo ! white people!

Rickets is the most dramatic example of a disease caused by vitamin D deficiency, but lack of vitamin D is also associated with increased risk of a growing number of common diseases.

Originally Posted by etdeceaz

What sort of circumstances - environmentally and evolutionarily - could have caused humans to have evolved with pure black or white skin? I mean that as in color, not ethnicity. I would appreciate as detailed a response as possible.

Do you really mean "pure black or white"? If so, I have no idea what you mean.

On the other hand, if you mean the range of skin colours that exist today, then the basic reasons are quite simple. Humans started in Africa and needed dark skin to protect them from the damaging effects of the sun (no clothes and no sunscreen). As they migrated out of Africa succeeding generations would have started suffering from vitamin D deficiency. In the usual way, those with lighter skin would have increased chances of reproduction and so populations with lighter skin evolved.

As Strange said, "pure" black and white is not a realistic concept. The context offered apparently speaks to the relative amount of melanin in skin. Melanincan serves akot of function -, antioxidant, metal sequestration, protection vs various forms of radiation - in fact it is reported that black fungi have infested the Chernobyl nuclear reactor. This may or may not be a simplee isolated population variable. Popualations with greater pigmentation also have greater incidence of sickle cell, tinea versicolor (tho it is more obvious in these folks). etc.