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Home , Human skin color

recent trends in evo-devo primatology and (paleo-)anthropology modern skin pigmentation modern pigmentation: latitude

Parra 07 function of pigmentation dark pigmentation: • protection against sunburn and • protection against photolysis of in cutaneous capillaries; folate is important in – rapidly dividing cells: embryogenesis (deficiency à neural tube defects); sperm production – melanin production regulation – nucleotide excision repair of UV-induced DNA damage function of melanin pigmentation

pigmentation:

• UVB-dependent vitamin D3 production in the skin; important for: – bone metabolism [Ca uptake] – innate immune response – cell proliferation and differentiation genetic regulation

: tyorsine à melanin

MC1R: melanin synthesis

Parra 07 melanocyte

Figure 1. Biochemistry and Histology of Different Skin Types. (A) Activation of the (MC1R) promotes the synthesis of eumelanin at the expense of pheomelanin, although oxidation of by tyrosinase (TYR) is required for synthesis of both types. The membrane-associated transport protein (MATP) and the -eyed dilution protein (P) are melanosomal membrane components that contribute to the extent of pigment synthesis within melanosomes. (B) There is a gradient of size and number in dark, intermediate, and ; in addition, melanosomes of are more widely dispersed.

Barsh 03 UVA and UVB

• UVA: 400 – 315 nm (3.10 – 3.94 eV) • UVB: 315 – 280 nm (3.94 – 4.43 eV)

– absorbed by O2, O3, H2O à altitudinal gradient à seasonal fluctuation UV annual mean (A) and annual variation (B)

UVA UVB

Jablonski & Chaplin 10 -genetic history of skin pigmentation

Juzenienne et al. 09 factors influencing human skin pigmentation

• geography: – latitude directly related to overall UV intensity à adaptive evolutionary tradeoff between folate protection and vitamin D3 production – seasonality of UVB availability à adaptive of facultative pigmentation (tanning) • sex – : greater need for vitamin D in females () à fairer skin than in males of the same population – sexual selection: preference of fair skin? (cf. Darwin) • out-of- population history – repeated independent adaptive evolution of fair skin developmental genomics: melanocortin receptor activity and skin pigmentation

Structure and activity of MC1R. (A) Depicted are the seven transmembrane helices of MC1R. The R307G , found in two , is positioned within helix 8, or the fourth intracellularloop. This amphipathic helix contains many conserved basic residues and is part of the intracellular receptor C terminus. (B) Partial loss of function of the R307G variant. For functional characterization, COS-7 cells were transiently transfected with constructs coding for the wild type (huMC1R) and the R307G variant. As a control, cells transfected with a plasmid encoding fluorescent protein (GFP) were used. Transfected cells were tested for agonist-induced cAMP accumulation (11). Shown are the mean ± SEM of three independent representative assays, each performed in duplicate. Lalueza-Fox et al. ‘07 (meta-)genomics and evo-devo genetic heterochrony

micro-array analysis of expression patterns of 7958 in macaques, and , from birth to adulthood

Somel et al., ‘09 evolution and development of “dwarfs” H. floresiensis facts • geological age: 12 - 70 ky • stature: 1m • brain size: 420ccm questions • modern human “microcephalic dwarf”? – developmental pathology • “” descendant?

• H. erectus descendant? – body and brain size reduction H. floresiensis “pathologies”

• proposed pathologies: 05 ‘ – microcephaly – Laron syndrome

(growth hormone insensivity) Gilbertal. et

– congenital hypothyroidism normal 8y-child microcephalic – ... 8y-child 09 ‘ Falk et al. Falket

Laron syndrome (origiginal publication Laron syndrome (full image) H. floresiensis Hershkovitz et al. ‘06) dwarf hippo brains

modern hippo: H. amphibius modern pygmy hippo: Choeropsis H. madagascarniensis liberiensis H. lemerlei

H. amphibius juvenile

EM Weston & AM Lister. Insular dwarfism in hippos and a model for brain size reduction in floresiensis. Nature 459, 85-88 (2009) brain size genes

Gilbert, Dobyns and Lahn (‘05). Genetic links between brain development and brain evolution. Nat. Rev. evo-devo of limb proportions Young et al, 2010 Development and the evolvability of human limbs

(A) The common genetic architecture of limbs, as demonstrated by their similar Hox patterning (gray, low expression; , primary expression) (6), reflects their serial homology and suggests a hierarchical limb covariation structure apportioned between and within limbs. Theoretical developmental and functional modules of the human limb are shown: stylopod (humerus and femur), zeugopod (radius/ulna, tibia/fibula), and autopod (hands, feet, and digits). (B) Covariation between developmental modules of the limbs in response to selection determines the phenotypic space (gray ellipses) and the independent evolvability of limbs. When correlations are low, phenotypic space is more evenly distributed (Upper Left). When correlations are high this space will tend toward individuals differing in size but with similar proportions (Bottom Right). The model predicts that the mosaic evolution of modern human limb proportions required reductions in integration. Young et al, 2010 Development and the evolvability of human limbs

(C) Humans (black circle) have relative limb proportions that are distinct from apes (gray circles) and quadrupedal monkeys ( circles). The net direction of evolutionary change was an increase to relative leg length and a smaller decrease in relative arm length and is approximately orthogonal to interspecific allometry of quadrupedal relative limb proportions (dashed line). (D) Selection in hominins occurred in at least two phases: (i) in early hominins such as the [Au. afarensis (AL-288-1) and BOU-12/1, gray, reconstructed] relative leg length increased with smaller changes to relative arm length [note: estimated IMI of Ar. ramidus is comparable to Au. afarensis], and (ii) in H. ergaster (KNM-WT15000) relative forearm length decreased and leg length further increased. This mosaic pattern indicates independent variation in the limbs and reduced integration. Locations of fossils are based on published descriptions and estimates. references

• Barsh, G. S. (2003). What controls variation in human skin ?. PLoS biology, 1(1), e27. • EM Weston & AM Lister. Insular dwarfism in hippos and a model for brain size reduction in . Nature 459, 85-88 (2009) • Falk, D., Hildebolt, C., Smith, K., Morwood, M. J., Sutikna, T., Wayhu Saptomo, E., & Prior, F. (2009). LB1’s virtual endocast, microcephaly, and hominin brain evolution. Journal of , 57(5), 597-607. • Gilbert, S. L., Dobyns, W. B., & Lahn, B. T. (2005). Genetic links between brain development and brain evolution. Nature Reviews Genetics, 6(7), 581-590. • Jablonski, N. G., & Chaplin, G. (2010). Human skin pigmentation as an adaptation to UV radiation. Proceedings of the National Academy of Sciences, 107(Supplement 2), 8962-8968. • Juzeniene, A., Setlow, R., Porojnicu, A., Steindal, A. H., & Moan, J. (2009). Development of different human skin : a review highlighting photobiological and photobiophysical aspects. Journal of Photochemistry and Photobiology B: Biology, 96(2), 93-100. • Lalueza-Fox, C., Römpler, H., Caramelli, D., Stäubert, C., Catalano, G., Hughes, D., ... & Hofreiter, M. (2007). A melanocortin 1 receptor suggests varying pigmentation among Neanderthals. Science, 318(5855), 1453-1455. • Parra, E. J. (2007). Human pigmentation variation: evolution, genetic basis, and implications for public health. American journal of physical anthropology, 134(S45), 85-105. • Somel, M., Franz, H., Yan, Z., Lorenc, A., Guo, S., Giger, T., ... & Khaitovich, P. (2009). Transcriptional neoteny in the human brain. Proceedings of the National Academy of Sciences, 106(14), 5743-5748. • Young, N. M., Wagner, G. P., & Hallgrímsson, B. (2010). Development and the evolvability of human limbs. Proceedings of the National Academy of Sciences, 107(8), 3400-3405.