Question

Name: Lab day & time: Human Skin Color Assignment Due: at the beginning of lab during the week of March 10-13 (no late assignments). You are welcome to discuss your ideas with others. However, your written answers must be original. Please write in complete sentences. Note: For this assignment, consider how selection acted on skin color in indigenous populations around the world. Evolution of Skin Color - The Conventional Explanation Until fairly recently, the leading explanation for the variation in skin colors in indigenous populations around the world was that darker skin evolved to protect against the harmful effects of UV light. 1. Propose an explanation for how skin cancer risk might have selected for darker skin color in early hominins who lived near the equator. Hint: address both conditions of natural selection.

Answer 1

If we hypothesize that the skin color that was there in hominids is light colored, but mutation and natural selection must have led to dark color near the equator.

Equator receives more UV rays from the sun. Absorption of UV rays can cause lot of mutations and cancer in the tissues of the humans. Especially skin cancer.So indigenous people who lived near the equator must have received lot of UV rays. This must have led to many people die due to the harmful effects. Excessive UV also may have resulted in some mutation in skin color gene. The mutation must have resulted in dark color and people with dark color may have had more selective advantage due to protection from UV rays. So more people with dark color may have survived in the hominins of those days. As the evolution went on, dark skin color got selected more and more because fo the selective advantage of the dark color.

Dark color is due to a pigment called melanin produced by melanocytes in the skin. Melanin absorbs UV rays and prevents it from passing deep in to the tissues. That is how the body tissues are protected from mutations and cancer. The protection the indigenous people got against these conditions has increased the frequency of the people with dark skin over generations leading to the evolution of the dark color over generations in the regions of more UV rays.

So, a variant in the skin color gene must have originated in hominins and it must have got selected over generations as it has advantage of not suffering from skin cancer.