It has been suggested that as a result this was a time of intense sexual rivalry between females due to their numbers exceeding those of males. This seems to be true of a lot of men. Northern Europe has fewer hours of sunlight compared with Africa, so the theory is that tribes migrating into Europe underwent a genetic mutation that resulted in the depigmentation of skin and hair. But in some parts of the world, such as central Africa, mutations that result in albinism or a significant depigmentation of a baby can provoke fear and superstition and sometimes even infanticide. The genes for blue eyes and blonde hair are recessive, meaning both parents must have the genes for them to be expressed in their offspring. In addition, before bottles of hydrogen peroxide became available, blonde hair in females could be interpreted as an honest signal of youth and therefore reproductive fitness. The traits are thought to have evolved among northern European tribes at the end of the last ice age. It has been theorised that the blonde hair and blue eyes seen in Caucasians are recent adaptations, dating from approximately 11, years ago. Research suggests that blondes feature more often as Playboy centerfolds than they do in women's magazines, and the percentage of blondes in each type of magazine exceeds the base rate of blondes in the normal population. Marilyn Monroe in Gentlemen Prefer Blondes natural or otherwise. For a female to choose a blond male he must be able to deliver resources mammoth , as his blond hair alone is not enough to turn her on. Individuals with lower levels of a melanin pigment called eumelanin are likely to have blonde hair. This would also help to explain the existence of blond males. Blond hair in males does not correlate with oestrogen levels as it does in females and blond hair in males is not a known indicator of fitness as it is in females. Although both natural and sexual selection have played a part in the evolution of the blue-eyed blonde, sexual selection was probably the primary force. Colour mutations can only proliferate in populations if they are seen as desirable and are sexually selected for.