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Impending Release of New Book:
Skin Its Natural History
In October 2006, the University of California Press will release
Nina Jablonski's new book on skin. For more information, please visit
their website at http://www.ucpress.edu/books/pages/10283.html
Fletcher Foundation Award
Dr. Nina Jablonski was awarded the Alphonse Fletcher, Sr. Fellowship for
her research, “Improving the Public Understanding of the Biological
and Social Meaning of Skin Color”. Announced by Alphonse Fletcher,
Jr., Chairman and CEO of Fletcher Asset Management, Inc., the Fletcher
Fellows include individuals who will receive a stipend of $50,000 for
work that contributes to improving race relations in American society and
furthers the broad social goals of the U.S. Supreme Court’s Brown
v. Board of Education decision of 1954. To read more about the Fletcher
Fellowships, see http://www.fletcherphilanthropy.org/
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MAJOR PUBLICATIONS
1. Jablonski, N.G. The evolution of human skin and
skin coloration. Annu. Rev. Anthropol. 33:585-623.
2. Jablonski, N.G. and Chaplin, G. (2000) The evolution of human skin coloration. J. Hum. Evol. 39:57-106.
3. Jablonski, N.G. (1998) Ultraviolet light-induced
neural tube defects in amphibian larvae and their implications for the
evolution of melanized pigmentation and declines in amphibian
populations. J. Herpetology 32:455-457.
4. Chaplin, G. and Jablonski, N.G. (1998) Comment on
hemispheric difference in skin color. Am. J. Phys. Anthrop. 107:221-224.
5. Jablonski, N.G. (1992) Sun, skin and spina bifida: An
exploration of the relationship between solar ultraviolet radiation, skin
colour and neural tube defects. In: Bruce, N.W. (Ed.), Proceedings of
the Fifth Annual Conference of the Australasian Society for Human Biology.
Perth, Centre for Human Biology, pp. 455-462. |
KEY PUBLICATION
JABLONSKI, NINA G. AND GEORGE CHAPLIN. 2000. The evolution of human skin
coloration. Journal of Human Evolution 39(1):57-106.
ABSTRACT
Skin color is one of the most conspicuous ways in
which humans vary and has been widely used to define human races. Here we
present new evidence indicating that variations in skin color are
adaptive, and are related to the regulation of ultraviolet (UV) radiation
penetration in the integument and its direct and indirect effects on
fitness. Using remotely sensed data on UV radiation levels, hypotheses
concerning the distribution of the skin colors of indigenous peoples
relative to UV levels were tested quantitatively in this study for the
first time.
The major results of this study are: (1) skin reflectance is strongly
correlated with absolute latitude and UV radiation levels. The highest
correlation between skin reflectance and UV levels was observed at 545
nm, near the absorption maximum for oxyhemoglobin, suggesting that the
main role of melanin pigmentation in humans is regulation of the effects
of UV radiation on the contents of cutaneous blood vessels located in the
dermis. (2) Predicted skin reflectances deviated little from observed
values. (3) In all populations for which skin reflectance data were
available for males and females, females were found to be lighter skinned
than males. (4) The clinal gradation of skin coloration observed among
indigenous peoples is correlated with UV radiation levels and represents
a compromise solution to the conflicting physiological requirements of
photoprotection and vitamin D synthesis.
The earliest members of the hominid lineage probably had a mostly
unpigmented or lightly pigmented integument covered with dark black hair,
similar to that of the modern chimpanzee. The evolution of a naked,
darkly pigmented integument occurred early in the evolution of the genus
Homo. A dark epidermis protected sweat glands from UV-induced injury,
thus insuring the integrity of somatic thermoregulation. Of greater
significance to individual reproductive success was that highly melanized
skin protected against UV-induced photolysis of folate (Branda and Eaton
1978, Science 201:625–626; Jablonski 1992, Proc. Australas. Soc.
Hum. Biol.5:455–462; 1999, Med. Hypotheses 52:581–582), a
metabolite essential for normal development of the embryonic neural tube
(Bower and Stanley, 1989, The Medical Journal of Australia 150:613–619;
Medical Research Council Vitamin Research Group 1991, The Lancet
338:31–37) and spermatogenesis (Cosentino et al. 1990, Proc. Natl.
Acad. Sci. USA 87:1431–1435; Mathur et al. 1977, Fertility
Sterility 28:1356–1360).
As hominids migrated outside of the tropics, varying degrees of
depigmentation evolved in order to permit UVB-induced synthesis of
previtamin D3. The lighter color of female skin may be required to permit
synthesis of the relatively higher amounts of vitamin D3 necessary during
pregnancy and lactation.
Skin coloration in humans is adaptive and labile. Skin pigmentation
levels have changed more than once in human evolution. Because of this,
skin coloration is of no value in determining phylogenetic relationships
among modern human groups. |
Click here to download a printable
version of this paper.
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