Please take care of me! (source) Child neglect is common in Papua New Guinea, even in regions where food is relatively abundant. Did juvenile hair color become lighter as a way to elicit maternal care?
If we exclude people of European descent, blond hair is most common among the natives of Oceania, specifically within a zone stretching from central and western Australia, through Papua New Guinea and into Melanesia and nearby islands. This coloration is due to a genetic variant of TYRP1 that is rare or nonexistent outside Oceania (Kenny et al., 2012).
Among central Australian Aborigines, blond hair varies by age and sex:
Up to 10 years of age the color distribution is approximately the same in both sexes at about 85% “fair” to 15% “dark.” Over the age of 11 years it is difficult to find a “fair” male while female “fairness” falls off more gradually.
[…] In the males the onset of darkening becomes apparent from about the 8th year. In adolescence the hair ranges from medium brown to black (observations in this group are very limited) while beyond 20 years practically all are in the “dark” category. […] In the females darkening becomes definite only after about the 20th year, and even in old age does not often exceed light brown. (Abbie & Adey, 1953)
We see the same age and sex pattern in Solomon Islanders:
An interesting hair phenotype that is sometimes seen in Island Melanesia (as well as among Australian Aborigines) is “blondism,” in which individuals exhibit the characteristic darkly pigmented skin of the region while also having blond hair. This trait was most commonly observed in children whose hair generally darkened around puberty (Robins, 1991). However, in some cases, blondism persists into adulthood, although the hair appears somewhat darker than what is seen in children (Norton et al., 2006).
This is similar to the situation in Europe, where blond hair likewise is more common among children and women (Shekar et al., 2008; Steggerda, 1941). Among Europeans, however, blond hair is much less specific to juveniles, being maintained throughout life in most individuals.
Origins and adaptive value
How did this “Oceanic” blondism come about? The evolutionary path may be analogous to that of European blondism.
European women naturally have hair that is more brightly and diversely colored (Shekar et al., 2008; Steggerda, 1941). This is consistent with a need to attract prospective mates, since bright and/or novel colors are more likely to be noticed and remembered. Most alleles aren’t sex-linked, so this kind of sexual selection would have spilled over on to European men, changing their hair color as well (Frost, 2006; Frost, 2008).
All of this implies that ancestral European women faced a competitive mate market. At higher latitudes, too many women had to compete for too few men, especially among hunter-gatherers. On the one hand, hunting distances were longer on average, thus increasing male mortality. On the other, men were less polygynous because of the higher costs of provisioning women and their offspring, especially during winter. This excess of females over males in the mate market was greatest on the continental steppe-tundra that covered most of Europe during the last ice age. Northern Asia also had steppe-tundra, but only in arid regions farther north where human occupation was not continuous, particularly at the height of the last ice age (Frost, 2006; Frost, 2008).
In equatorial Oceania, the evolutionary path may have been both similar and different. As in Europe, there is an aesthetic preference for blond hair:
In Samoa, all fair hair is considered 'ena'ena, a word that is usually translated as brown, although when English-speaking Samoans use this term in reference to hair, they typically gloss it as 'blond'. This makes sense since, when one is bleaching Polynesian hair, it goes through a series of reddish- brown shades prior to arriving at blond, and even then retains a reddish hue. When describing hair, Samoans specify the actual shade of 'blond' by using certain modifiers with 'ena'ena, such as 'ena'ena manaia, which literally means 'really nice brown hair', but which refers to a very fair reddish colour.
The hair of female spirits is most commonly said to be 'ena'ena manaia, and they are wont to decorate it with a red hibiscus (Mageo, 1994).
But what is the adaptive value for young children? They are, after all, the ones who most often have this hair color. What kind of selection pressure could have favored blond children?
One possibility is child neglect. Papua New Guinea has a relatively high rate of child malnutrition—35% on average, with some regions having rates as high as 78%. Yet malnourished children are found in areas that have an apparent surplus of food. Lepowsky (1987, p. 75) notes that “the reported pattern of child malnutrition did not follow environmental or ecological patterns but cultural ones.” The ultimate cause seems to be “maternal detachment”:
These women take a guarded attitude toward infants, extending the greatest amount of their affection and parental care toward children who are physically strong and who survive the first couple of years of life. (Lepowsky, 1987, p. 78)
For this reason, child naming is delayed for a few weeks after birth, and the ritual thanking of the father’s kin is delayed for about six months. Mothers take for granted that their offspring may not survive this period.
Thus, in equatorial Oceania, child survival depends very much on the degree of maternal attachment, i.e., the mother’s fondness for her child. Has this factor favored “cute” features, like blond hair? Is blondism a child’s way of eliciting more maternal care during infancy?
Abbie, A.A. & W.R. Adey. (1953). Pigmentation in a central Australian tribe with special reference to fair-headedness, American Journal of Physical Anthropology, 11, 339-359.
Frost, P. (2008). Sexual selection and human geographic variation, Special Issue: Proceedings of the 2nd Annual Meeting of the NorthEastern Evolutionary Psychology Society. Journal of Social, Evolutionary, and Cultural Psychology, 2(4),169-191. http://220.127.116.11/jsec/articles/volume2/issue4/NEEPSfrost.pdf
Frost, P. (2006). European hair and eye color - A case of frequency-dependent sexual selection? Evolution and Human Behavior, 27, 85-103 http://www.sciencedirect.com/science/journal/10905138
Kenny, E.E., N.J. Timpson, M. Sikora, M-C. Yee, A. Moreno-Estrada, C. Eng, S. Huntsman, E.G. Burchard, M. Stoneking, C.D. Bustamante, & S. Myles (2012). Melanesian blond hair is caused by an amino acid change in TYRP1, Science, 336, 554.
Lepowsky, M. (1987). Food taboos and child survival: A case study from the Coral Sea, in N. Scheper-Hughes (ed.) Child Survival: Anthropological Perspectives on the Treatment and Maltreatment of Children, (pp. 71-92), Springer.
Mageo, J.M. (1994). Hairdos and Don'ts: Hair Symbolism and Sexual History in Samoa, Man, New Series, 29 (2) 407-432
Norton, H.L., J.S. Friedlaender, D.A. Merriwether, G. Koki, C.S. Mgone, & M.D. Shriver. (2006). Skin and Hair Pigmentation Variation in Island Melanesia, American Journal of Physical Anthropology, 130, 254–268.
Shekar, S.N., D.L. Duffy, T. Frudakis, G.W. Montgomery, M.R. James, R.A. Sturm, & N.G. Martin. (2008). Spectrophotometric methods for quantifying pigmentation in human hair—Influence of MC1R genotype and environment. Photochemistry and Photobiology, 84, 719–726.
Steggerda, M. (1941). Change in hair color with age, Journal of Heredity, 32, 402-403.