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Saturday
Jan102009

Gene Flow

New and improved versions of genes occasionally arise, but they can't be important unless they spread. This chapter talks about some of the factors that affected the spread of new mutations, ranging from Greek colonies to the Himalayas. In particular, we talk about some of the historical factors that may have influenced the spread of the allele causing blue eyes.

 

Reader Comments (2)

<Blockquote>In particular, we talk about some of the historical factors that may have influenced the spread of the allele causing blue eyes.
</Blockquote>
Hmm, I think it ought to be borne in mind that blue coloured contact lenses and, much more commonly, lenses to make natural blue eyes look even bluer, are mainly used by women . Basically women think they help them get noticed . Now I don't suggest she wears colour enhancing contacts but would Cameron Diaz be as eye catching without her unusual china blue peepers. (Women seem to think blonde hair gets noticed too.) Blue eyes are not a secondary sexual characteristic obviously, men have them , they are not a sign of fertility like a hourglass figure. So there was a time when just having all the sexually alluring signs of fertility was not enough to ensure a woman could reproduce, she had to stand out from the others somehow., hence an advantage for novel eye colours, hazel, green, and brown. (yes brown is very much an unusual colour, most of the world has 'black' eyes)

A period where the standard eye colour people (women) were reproducing at a greatly reduced rate explains how common blue (and other coloured) eyes are today while also explaining why blue eyes never reached fixation anywhere. The following also applies to blue eyes I think

"If the selection were frequency-independent, i.e., constant, the incidence of blond hair should steadily rise until it reached fixation. This would happen even if one assumes a very slight selective advantage

January 31, 2009 | Unregistered CommenterTod

Some say " the gene for blue eyes codes for paler skin coloring in many vertebrates and hence might have piggybacked along with lighter skin"

Sunbathers: Beware the A-ray

Redheads make only one of the two main types of melanin, a red-yellow pigment called pheomelanin. They cannot make black-brown melanin, or eumelanin. Pheomelanin is the less stable of the two and is more likely to generate radicals. Non-redheads have both types of pigment, but produce more eumelanin when they tan. "You could imagine that the benefit of a tan is that it is switching the ratio from high pheomelanin/low eumelanin to higher eumelanin, which may explain why very dark-skinned people or people who tan are less likely to develop melanoma," says Fisher.

Why was white skin not formed by progressive reduction of eumelanin ?
Pheomelanin was not necessary to have pale skin and increases the risk of cancer (something that that producing white skin by simply lowering eumelanin does not do). Pheomelanin must have some advantage that outweighs its cancer promoting effect.

It produces novel hair colours

It has been demonstrated that the ratio of eumelanin to pheomelanin in ocular tissue does not differ in blue or brown eyes (Menon et al.,


The only advantage of blue eyes is the way they look.

February 10, 2009 | Unregistered CommenterTod

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