The world today has many creatures, living organisms both great and small, from the largest of sea creatures to the smallest of microorganisms, to you and me. Our genetic ancestors lived in and came from gene pools and migrated with our ever changing earth from land bridge to ocean crossing. Melanin, is our bodies reacting different to the Sun - for example, making for the pigment of our skin the colour it is. Darker skin hues are found in peoples in warmer environments, as for blonde people with blue eyes were bleached by the sun over generations of early human. Diet also a factor to take into consideration, since to be blunt 'we are what we eat'. The food we've managed to hunt, fish and forage, a factor relative to the local habitat and ecosystem will have effected how many calories our brains were fed in order for growth, or how much calcium and proteins I should imagine.