Stefan - You were right on target! No misunderstanding at all.

This same evolutionary process is seen in humans.

Once upon a time, we were all the same color and size, and as time passed on different genes developed.

depending on where "tribes" were located, the amount of Melanin decreased in some parts of the word, and increased in others.

Thats why humans come in assorted colors also.

I called a friend of color "melanistic" once, he laughed at me and said he'd been called a lot of things (use your imagination) and Melanistic was never one of them.

The conversation started over a sunburn I got, we had both been out in the sun equal amounts of time, but his very dark skin did not burn, and my overly (amelanistic) Caucasian skin fried to a reddish hue!

This change in skin pigmentation was probably due to the early tribes that moved (near you) to the cooler European climates, they no longer required all of the dark pigmentation, so it simply faded away.

Regards,
Wayne