Marilyn Monroe in Gentlemen Prefer Blondes natural or otherwise. Blonde hair is almost certainly a sexually selected trait in women. This seems to be true of a lot of men. Chimpanzee wearing spectacles Photograph: Public Domain Carole replies: Ten years after he published On the Origin of Species in , Darwin started to research the sexual selection of blonde hair in women in preparation for his book The Descent of Man and Selection in Relation to Sex , which was published in Unfortunately he was unable to find enough data to support his theory that blonde hair is sexually selected and had to drop the subject.
Today there are plenty of theories about the evolution of blonde hair and the science of genetics has furthered the debate. Research on variation in human hair colouration has shown that mutations in genes that are involved in the synthesis of melanin pigments are largely responsible. Individuals with lower levels of a melanin pigment called eumelanin are likely to have blonde hair. It has been theorised that the blonde hair and blue eyes seen in Caucasians are recent adaptations, dating from approximately 11, years ago.
The traits are thought to have evolved among northern European tribes at the end of the last ice age. 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.
As regards natural selection, depigmentation allows greater penetration of the skin by ultraviolet B UVB , which is needed to synthesise previtamin D3. 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.
Late Palaeolithic females in southern Europe and Africa could forage for food and feed themselves and their infants, with males occasionally supplementing their diet with meat. In northern Europe, however, where ice covered much of the terrain, people were dependent on meat. Bands of men went in search of herds of prehistoric bison or mammoth. These hunting trips were dangerous, resulting in many fatalities. 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.
The theory is that when given the choice, Pelaeolithic males chose blondes, who stood out from their rivals. 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. This is because postmenopausal women rarely retain the flaxen locks of their youth, of course eventually becoming grey grannies.
Interestingly, Aboriginal tribes have evolved blonde hair in females independently of the Nordic blonde. 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.
Colour mutations can only proliferate in populations if they are seen as desirable and are sexually selected for. There are higher numbers of females born blonde than males and retention of blonde hair into adulthood is a sexually selected indicator of fitness in females.
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. A blue-eyed male with a brown-eyed mate would not have the same assurance the resulting brown-eyed infant was his child and therefore worthy of a slice of the mammoth he risked his life trapping and slaughtering and then spent days dragging back across miles of icy tundra. 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. In addition, females don't select for physical appearance to the degree that men do. 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.
Blondes do not seem to have lost any of their popularity since the end of the last ice age. 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.