About two million years ago on the continent of Africa marked the beginning of human history. Thanks to genetic variation, some humans were born with darker skin because melanin is more abundant. Melanin is a naturally produced polymer found in the skin. It acts like a sunscreen, protecting folate from the harmful effects of UV light emitted from the scorching sun of the tropical regions. Our darker-skinned ancestors were therefore able to maintain a level of folate, which is vital in preventing birth defects of a baby's brain and spinal cord. Natural selection kicked in over thousands of generations as genetically darker-skinned people could produce healthier offspring, spreading their dark-skinned genes.
When our ancestors started to move northwards and out of Africa, they are getting less and less sunlight because the light hits the earth at a lower angle in higher latitudes. Weaker UV light means that our body will synthesise less Vitamin D, which is vital for reproduction. Vitamin D deficiency is linked to underdevelopment of the uterus and an inability to form normal mature eggs, resulting in infertility. Owing to genetic variation, those born with lighter skin were still able to produce enough Vitamin D for reproductive health. Natural selection once again kicked in here. The genetically lighter-skinned people grew stronger and were more able to reproduce, spreading their light-skinned genes. Evolution over many generations results in the average skin colour of the populations exposed to less UV radiation gradually becoming lighter.
| JPC Monthly Newsletter | |
| Editor： | Police Public Relations Branch, 11/F Arsenal House, Police Headquarters, No. 1 Arsenal Street, Wan Chai, HK. |
| Tel： | 2860 6157 |
| Fax： | 2200 4304 |
| JPC homepage： | http://www.hkpjpc.org.hk |
| Police homepage： | http://www.police.gov.hk |