I had a few comments from creationists left on my blog lately. One from somebody who identified themselves as '?':

i have a question...how did creatures change from generation to generation to be better suited for their environments? i mean, if i moved to (i don't know) africa, and i had kids with an another person with my skin color, the color wouldn't change in my great grand children to make them better suited for their environments. it's called mating with another type of your own species, not evolution right?

To start off I'll briefly talk about how variation comes about. If the first self-replicating molecule could create perfect copies of itself, there would be no evolution, the world would be full of clones of that original molecule. Evolution by natural selection requires variation for it to act upon. Originally all that variation came about by mutations, either errors copying the DNA (or RNA), or by damage from cosmic rays. If the changes were advantageous the mutation would spread throughout the population. Around 1-1.5 billion years ago another tool to increase the variation evolved sexual reproduction, no longer did life descended from those cells create clones of themselves, instead they would re-combine their DNA with that of another, ensuring that children are not clones of the parent. This variation also provided something else for natural selection to act upon.

Darker skin evolved in humans in Africa around 1.5 million years ago, back in the time of Homo ergaster, as we began to lose our hair. At some point mutations happened in a gene (or genes) which darkened our skin, this may of been gradual or happened in a single mutation. This mutation was beneficial because it better protected the body from ultra-violent radiation (previously our hair protected us against it), and alas it spread throughout the population.

Around 40000 years ago, Homo sapiens began to move north into Europe. At this point another mutation happened, we know it was a change in a single nucleotide, out of 3.1 billion which make up our DNA. This produced a pale skinned individual. Further north we required less protection from UV radiation so maintaining our dark skin became less important, but this also had a benefit, it increased the amount of vitamin D that Europeans who carried this mutation produced. Some lines of evidence such as cave paintings suggest some Europeans could of been dark skinned up until just 13000 years ago, today however 99% of Europeans carry the mutation.

The original question set up a premise that the skin of their descendants would not darken from living in Africa. Obviously it is impossible to predict random mutations in the future, and the selective value of dark or light skin is less than it used to be before we invented sun block and had better diets. But if the climate of Africa remained the same, and if you could stop your descendants from mating outside of your family (both of which aren't realistic in practice) the skin of your descendants would almost certainly darken. We've seen skin colour changes happen multiple times independently in human populations in the past, and they will undoubtedly happen in the future.

Given enough time if you could prevent your descendants from breeding with the rest of Homo sapiens they would eventually form a new species, enough mutations would of happened in each population, and as no changes would be passed back and forth between the two groups eventually they'd no longer be compatible, of course this could take anywhere from tens of thousands to hundreds of thousands of years for the differences to gradually build up.

Take our friend Su Kong, if the Earth went into a major ice age in the late 19th century and the rest of us were freezing to death around him (presumably we'd have to forget how to make hats too) his descendants could well make up Homo thefuture while Homo sapiens are strewn across a thin layer of dirt - so much for the species made in god's image!

Changes in our genes happen over time, and natural selection will act upon them.

it just doesn't make sense to me. i mean, all you have to do is think about evolution and it just doesnt make sense. u can't just scratch the surface. and also

Once you understand evolution it makes perfect sense, you develop an understanding, a real understanding of how life on Earth is so diverse, you see the interconnectedness of all life, how we are all descended from a four billion year old self-replicating molecule and you see that nothing is stationary and things are constantly changing.

how has evolution been scientifically proven? the only facts ive ever seen have DISPROVEN it.

I've never seen facts that disprove it, in fact everything has gone evolution's way, if genetics worked differently evolution could of been falsified etc. If anybody finds fossil rabbits in the pre-Cambrian that'll put a sizeable hole in the evolution by natural selection boat. If you're reading creationist sources, of which I am familiar, well let's just say somebody who spends their time studying the bible instead of the world probably isn't in a position to know a lot about the world.