Biophysical evidence to support and extend the vitamin D-folate hypothesis as a paradigm for the evolution of human skin pigmentation
Lucock, M. D., Jones, P. R., Veysey, M., Thota, R., Garg, M., Furst, J., Martin, C., Yates, Z., Scarlett, C. J., Jablonski, N. G., Chaplin, G., & Beckett, E. L. (2021). Biophysical evidence to support and extend the vitamin D-folate hypothesis as a paradigm for the evolution of human skin pigmentation. American Journal of Human Biology, Early View, e23667. doi:10.1002/ajhb.23667
Objective – To test the “vitamin D-folate hypothesis for the evolution of human skin pigmentation.”
Methods – Total ozone mapping spectrometer (TOMS) satellite data were used to examine surface UV-irradiance in a large (n = 649) Australian cross-sectional study population. Genetic analysis was used to score vitamin D- and folate-related gene polymorphisms (n = 22), along with two pigmentation gene variants (IRF4-rs12203592/HERC2-rs12913832). Red cell folate and vitamin D3 were measured by immunoassay and HPLC, respectively.
Results – Ultraviolet radiation (UVR) and pigmentation genes interact to modify blood vitamin levels; Light skin IRF4-TT genotype has greatest folate loss while light skin HERC2-GG genotype has greatest vitamin D3 synthesis (reflected in both TOMS and seasonal data). UV-wavelength exhibits a dose–response relationship in folate loss within light skin IRF4-TT genotype (305 > 310 > 324 > 380 nm). Significant vitamin D3 photosynthesis only occurs within light skin HERC2-GG genotype, and is maximal at 305 nm. Three dietary antioxidants (vitamins C, E, and β-carotene) interact with UVR and pigmentation genes preventing oxidative loss of labile reduced folate vitamers, with greatest benefit in light skin IRF4-TT subjects. The putative photosensitiser, riboflavin, did not sensitize red cell folate to UVR and actually afforded protection. Four genes (5xSNPs) influenced blood vitamin levels when stratified by pigmentation genotype; MTHFR-rs1801133/rs1801131, TS-rs34489327, CYP24A-rs17216707, and VDR-ApaI-rs7975232. Lightest IRF4-TT/darkest HERC2-AA genotype combination (greatest folate loss/lowest vitamin D3 synthesis) has 0% occurrence. The opposing, commonest (39%) compound genotype (darkest IRF4-CC/lightest HERC2-GG) permits least folate loss and greatest synthesis of vitamin D3.
Conclusion – New biophysical evidence supports the vitamin D-folate hypothesis for evolution of skin pigmentation.
The constraints of racialization: How classification and valuation hinder scientific research on human variation
Lasisi, T. (2021). The constraints of racialization: How classification and valuation hinder scientific research on human variation. American Journal of Physical Anthropology, 175(2), 376-386. doi:10.1002/ajpa.24264
Human biological variation has historically been studied through the lens of racialization. Despite a general shift away from the use of overt racial terminologies, the underlying racialized frameworks used to describe and understand human variation still remain. Even in relatively recent anthropological and biomedical work, we can observe clear manifestations of such racial thinking. This paper shows how classification and valuation are two specific processes which facilitate racialization and hinder attempts to move beyond such frameworks. The bias induced by classification distorts descriptions of phenotypic variation in a way that erroneously portrays European populations as more variable than others. Implicit valuation occurs in tandem with classification and produces narratives of superiority/inferiority for certain phenotypic variants without an objective biological basis. The bias of racialization is a persistent impediment stemming from the inheritance of scientific knowledge developed under explicitly racial paradigms. It is also an internalized cognitive distortion cultivated through socialization in a world where racialization is inescapable. Though undeniably challenging, this does not present an insurmountable barrier, and this bias can be mitigated through the critical evaluation of past work, the active inclusion of marginalized perspectives, and the direct confrontation of institutional structures enforcing racialized paradigms.
Deeper than the surface: Exploring symbolic cultural cues behind skin color among three groups of women of Chinese heritage
Chen, H.-Y., & Jablonski, N. G. (2021). Deeper than the surface: Exploring symbolic cultural cues behind skin color among three groups of women of Chinese heritage. American Journal of Cultural Sociology. doi:10.1057/s41290-020-00124-9
We integrated cosmetic and appearance-related scenario elicitation and in-depth interviews to explore aesthetic attitudes toward skin color in bicultural contexts among three groups of emerging Chinese adults. Results indicated that Chinese women, who grew up in China until age 18 and then moved to the US, generally leaned toward Chinese culture, found lighter skin more beautiful, and chose shades of makeup foundation lighter than their skin color. Chinese adoptees, raised in the US by Euro-American parents, leaned toward Euro-American culture, considered tanned skin more attractive, and chose darker colored foundations in most social contexts other than professional. Chinese Americans, raised in the US by first-generation Chinese parents, expressed mixed preferences. Women’s preferences revealed how everyday decisions reflect cultural beliefs and symbolic values behind skin color, suggesting that attitude formation is contextually dependent. People favor different shades of foundation makeup for different occasions, suggesting agentic awareness and the use of behavioral modification to gain acceptance in a given context. Appearance manipulation is a form of self-expression and conveys sociocultural cues. Understanding subtle sociocultural meanings and aesthetics in complex cultural contexts has significant implications for body image and colorism-related research, promoting the exploration of cultural influences on appearance, ideal skin color internalization, and decision-making.
High-throughput phenotyping methods for quantifying hair fiber morphology
Lasisi, T., Zaidi, A. A., Webster, T. H., Stephens, N. B., Routch, K., Jablonski, N. G., & Shriver, M. D. (2021). High-throughput phenotyping methods for quantifying hair fiber morphology. Scientific Reports, 11(1), 11535. doi:10.1038/s41598-021-90409-x
Quantifying the continuous variation in human scalp hair morphology is of interest to anthropologists, geneticists, dermatologists and forensic scientists, but existing methods for studying hair form are time-consuming and not widely used. Here, we present a high-throughput sample preparation protocol for the imaging of both longitudinal (curvature) and cross-sectional scalp hair morphology. Additionally, we describe and validate a new Python package designed to process longitudinal and cross-sectional hair images, segment them, and provide measurements of interest. Lastly, we apply our methods to an admixed African-European sample (n = 140), demonstrating the benefit of quantifying hair morphology over classification, and providing evidence that the relationship between cross-sectional morphology and curvature may be an artefact of population stratification rather than a causal link.
The evolution of human skin pigmentation involved the interactions of genetic, environmental, and cultural variables
Jablonski, N. G. (2021). The evolution of human skin pigmentation involved the interactions of genetic, environmental, and cultural variables. Pigment Cell & Melanoma Research, 34(4), 707-729. doi:10.1111/pcmr.12976
The primary biological role of human skin pigmentation is as a mediator of penetration of ultraviolet radiation (UVR) into the deep layers of skin and the cutaneous circulation. Since the origin of Homo sapiens, dark, protective constitutive pigmentation and strong tanning abilities have been favored under conditions of high UVR and represent the baseline condition for modern humans. The evolution of partly depigmented skin and variable tanning abilities has occurred multiple times in prehistory, as populations have dispersed into environments with lower and more seasonal UVR regimes, with unique complements of genes and cultural practices. The evolution of extremes of dark pigmentation and depigmentation has been rare and occurred only under conditions of extremely high or low environmental UVR, promoted by positive selection on variant pigmentation genes followed by limited gene flow. Over time, the evolution of human skin pigmentation has been influenced by the nature and course of human dispersals and modifications of cultural practices, which have modified the nature and actions of skin pigmentation genes. Throughout most of prehistory and history, the evolution of human skin pigmentation has been a contingent and non‐deterministic process.
Social and affective touch in primates and its role in the evolution of social cohesion
Jablonski, N. G. (2021). Social and affective touch in primates and its role in the evolution of social cohesion. Neuroscience, 464, 117-125. doi:10.1016/j.neuroscience.2020.11.024
Primates are long-lived, highly social mammals who maintain long-term social bonds and cohesive social groups through many affiliative mechanisms, foremost among them social touch. From birth through adulthood, social touch – primarily mutual grooming – creates and maintains relationships of trust and reliance, which are the basis for individual physical and emotional well-being and reproductive success. Because social touch helps to establish, maintain, and repair social alliances in primates, it contributes to the emotional stability of individuals and the cohesion of social groups. In these fundamental ways, thus, social touch supports the slow life histories of primates. The reinforcing neurochemistry of social touch insures that it is a pleasurable activity and this, in turn, makes it a behavioral commodity that can be traded between primates for desirable rewards such as protection against future aggression or opportunities to handle infants. Social touch is essential to normal primate development, and individuals deprived of social touch exhibit high levels of anxiety and lower fertility compared to those receiving regular social touch. Understanding the centrality of social touch to primate health and well-being throughout the lifespan provides the foundation for appreciating the importance of social touch in human life.
Skin color and race
Jablonski, N. G. (2021). Skin color and race. American Journal of Physical Anthropology, 175(2), 437-447. doi:10.1002/ajpa.24200
Skin color is the primary physical criterion by which people have been classified into groups in the Western scientific tradition. From the earliest classifications of Linnaeus, skin color labels were not neutral descriptors, but connoted meanings that influenced the perceptions of described groups. In this article, the history of the use of skin color is reviewed to show how the imprint of history in connection with a single trait influenced subsequent thinking about human diversity. Skin color was the keystone trait to which other physical, behavioral, and culture characteristics were linked. To most naturalists and philosophers of the European Enlightenment, skin color was influenced by the external environment and expressed an inner state of being. It was both the effect and the cause. Early investigations of skin color and human diversity focused on understanding the central polarity between “white” Europeans and nonwhite others, with most attention devoted to explaining the origin and meaning of the blackness of Africans. Consistently negative associations with black and darkness influenced philosophers David Hume and Immanuel Kant to consider Africans as less than fully human and lacking in personal agency. Hume and Kant’s views on skin color, the integrity of separate races, and the lower status of Africans provided support to diverse political, economic, and religious constituencies in Europe and the Americas interested in maintaining the transatlantic slave trade and upholding chattel slavery. The mental constructs and stereotypes of color-based races remained, more strongly in some places than others, after the abolition of the slave trade and of slavery. The concept of color-based hierarchies of people arranged from the superior light-colored people to inferior dark-colored ones hardened during the late seventeenth century and have been reinforced by diverse forces ever since. These ideas manifest themselves as racism, colorism, and in the development of implicit bias. Current knowledge of the evolution of skin color and of the historical development of color-based race concepts should inform all levels of formal and informal education. Awareness of the influence of color memes and race ideation in general on human behavior and the conduct of science is important.
Microscopical discrimination of human head hairs sharing a mitochondrial haplogroup
Koch, S. L., Liebowitz, C., Shriver, M. D., & Jablonski, N. G. (2021). Microscopical discrimination of human head hairs sharing a mitochondrial haplogroup. Journal of Forensic Sciences, 66(1), 56-71. doi:10.1111/1556-4029.14560
In forensic analyses, determining the level of consensus among examiners for hair comparison conclusions and ancestry identifications is important for assessing the scientific validity of microscopical hair examinations. Here, we present data from an interlaboratory study on the accuracy of microscopical hair comparisons among a subset of experienced hair examiners currently analyzing hair in forensic laboratories across the United States. We examined how well microscopical analysis of hair can reliably be used to differentiate hair samples, many of which were macroscopically similar. Using cut hair samples, many sharing similar macroscopic and microscopic features, collected from individuals who share the same mitochondrial haplogroup as an indication of genetic relatedness, we tested multiple aspects that could impact hair comparisons. This research tested the extent to which morphological features related to ancestry and hair length influence conclusions. Microscopical hair examinations yielded accurate assessments of inclusion/exclusion relative to the reference samples among 85% of the pairwise comparisons. We found shorter hairs had reduced levels of accuracy and hairs from populations examiners were not familiar with may have impacted their ability to resolve features. The reliability of ancestry determinations is not yet clear, but we found indications that the existing categories are only somewhat related to current ethnic and genetic variation. Our results provide support for the continued utility of microscopical comparison of hairs within forensic laboratories and to advocate for a combined analytical approach using both microscopical analysis and mtDNA data on all forensic analyses of hair
Examining “race” in physiology
Wolf, S. T., Jablonski, N. G., & Kenney, W. L. (2020). Examining “race” in physiology. American Journal of Physiology-Heart and Circulatory Physiology, 319(6), H1409-H1413. doi:10.1152/ajpheart.00698.2020
Racial disparities in cardiovascular and cerebrovascular health outcomes are well described, and recent research has shed light on the mechanistic underpinnings of those disparities. However, “race” is a social construct that is poorly defined and continually evolving and is historically based on faulty premises. The continued categorization by race in physiological research suggests that there are inherent differences between races, rather than addressing the specific underlying factors that result in health disparities between groups. The purpose of this Perspectives article is to provide a brief history of the genesis of categorization by race, why such categorization should be reconsidered in physiology research, and offer recommendations to more directly investigate the underlying factors that result in group disparities in cardiovascular and cerebrovascular health.
Mesopithecus pentelicus from Zhaotong, China, the easternmost representative of a widespread Miocene cercopithecoid species
Jablonski, N.G., Ji, X., Kelley, J., Flynn, L.J., Deng, C., & Su, D.F. (2020). Mesopithecus pentelicus from Zhaotong, China, the easternmost representative of a widespread Miocene cercopithecoid species. Journal of Human Evolution, 146, 102851. doi:10.1016/j.jhevol.2020.102851
A dentate mandible and proximal femur of Mesopithecus pentelicus Wagner, 1839 are described from the Shuitangba lignite mine in Zhaotong Prefecture, northeastern Yunnan Province, China. The remains were retrieved from sediments just below those that yielded a juvenile Lufengpithecus cranium and are dated at about ∼6.4 Ma. The mandible and proximal femur were found in close proximity and are probably of the same individual. The lower teeth are metrically and morphologically closely comparable with those of confirmed M. pentelicus from Europe, and on this basis, the specimen is assigned to this species. The anatomy of the proximal femur indicates that the Shuitangba Mesopithecus was a semiterrestrial quadruped that engaged in a range of mostly arboreal activities, including walking, climbing, and occasional leaping, with an abducted hip joint. The Shuitangba Mesopithecus is dentally typical for the genus but may have been more arboreal than previously described for M. pentelicus. M. pentelicus is well known from late Miocene (MN 11–12) sites in Europe and southwest Asia. Its estimated average rate of dispersal eastward was relatively slow, although it could have been episodically more rapid. The presence of a colobine, only slightly lower in the same section at Shuitangba that produced Lufengpithecus, is one of the only two well-documented instances of the near or actual co-occurrence of a monkey and ape in the Miocene of Eurasia. At Shuitangba, M. pentelicus occupied a freshwater-margin habitat with beavers, giant otters, swamp rabbits, and many aquatic birds. The presence of M. pentelicus in southwest China near the end of the Miocene further attests to the ecological versatility of a species long recognized as widespread and adaptable. The modern colobines of Asia, some or all of which are probable descendants of Mesopithecus, have gone on to inhabit some of the most highly seasonal and extreme habitats occupied by nonhuman primates.
New fossils of Mesopithecus from Hasnot, Pakistan
Khan, M.A., Kelley, J., Flynn, L.J., Babar, M.A., & Jablonski, N.G. (2020). New fossils of Mesopithecus from Hasnot, Pakistan. Journal of Human Evolution, 145, 102818. doi:10.1016/j.jhevol.2020.102818
Here, we report on a new collection of mostly isolated molars of a colobine monkey from near Hasnot on the Potwar Plateau of Pakistan. The specimens are from three late Miocene localities, with ages constrained to between 7.9 and 7.1 Ma. Morphological and metrical comparisons of the new Hasnot molars with those of previously recognized Mesopithecus species and living Asian colobines lead to the conclusion that the Hasnot colobine is most probably Mesopithecus, but not Mesopithecus pentelicus. The most morphologically distinctive aspect of the Hasnot specimens is the lower third molars, which exhibit large and bulbous protoconids set off by deeply incised mesial buccal and median buccal clefts and large, broad distobuccally placed hypoconulids. Colobine specimens previously recovered from the Potwar Plateau have been assigned to Mesopithecus sivalensis, but because these specimens have not yet been fully described, a detailed comparison with the new Hasnot specimens is not yet possible. For these reasons, we assign the new Hasnot colobine fossils to cf. Mesopithecus sp. Mesopithecus was one of the most widespread and successful of late Miocene primates. As a colobine equipped with features of the molar teeth, limbs, and, presumably, gut enabling it to succeed in more highly seasonal woodland environments, Mesopithecus was able to rapidly disperse into and adapt to the conditions in South Asia brought about by profound climatic and concomitant environmental change during the latest Miocene.
The biology of human hair: A multidisciplinary review
Koch, S.L., Tridico, S.R., Bernard, B.A., Shriver, M.D., & Jablonski, N.G. (2020). The biology of human hair: A multidisciplinary review. American Journal of Human Biology, 32(2), e23316. doi:10.1002/ajhb.23316
In the last century, human scalp hair morphology has been studied from multiple, and sometimes mutually exclusive, perspectives by anthropologists, biologists, geneticists, forensic scientists, and cosmetic scientists. Here, we review and synthesize historical and current research on hair to better understand the scientific basis and biological implications of hair microstructure and morphology. We revisit the origins of existing nomenclature regarding hair morphology and classifications, discuss the currently recognized limitations to hair analysis within the varied scientific disciplines studying hair, point out aspects of hair biology that remain unknown, and the great potential for integrating these diverse perspectives and expertise in future scientific investigations, while highlighting the benefits of combining nondestructive microscopical analysis with chemical and genomic analyses for explicating hair biology. Further, we propose consensus terminology for root growth stages through descriptions and images that will aid in the morphological and microscopical analysis of human scalp hair, thereby reducing confusion and the promulgation of inaccurate information that is presently in the literature.
A cross-cultural exploration on the psychological aspects of skin color aesthetics: Implications for sun-related behaviour
Chen, H.-Y., Robinson, J. K., & Jablonski, N. G. (2020). A cross-cultural exploration on the psychological aspects of skin color aesthetics: Implications for sun-related behaviour. Translational Behavioral Medicine, 10(1), 234-243. doi:10.1093/tbm/ibz063
Sociocultural values toward skin color manifest in daily behaviors, such as sun-seeking behaviors in Euro-American culture and sun-protective behaviors in Chinese culture. However, little research has investigated how attitudes toward skin color affect sun-related behaviors in the face of conflicting cultural values. This study explores how sociocultural contexts shape attitudes toward skin color and sun-related behaviors in three groups of genetically Chinese women, located on a spectrum from predominantly Chinese culture to predominantly Euro-American culture. Using ethnographic and qualitative comparative approaches, interviews were conducted with (a) 15 Chinese women (Mage = 25; SD = 2.73) who grew up in mainland China until at least age 18 years and then moved to the United States, (b) 15 second-generation Chinese Americans (Mage = 20; SD = 1.16) raised in the United States by Chinese parents, and (c) 18 Chinese adoptees (Mage = 21; SD = 1.13) raised in the United States by Euro-American parents. Overall, Chinese women leaned toward Chinese culture, preferred lighter skin, and engaged in more sun-protection practices. Chinese adoptees leaned toward Euro-American culture, preferred tanned skin and sun-seeking behaviors, and experienced more sunburns. Chinese Americans had mixed results, exemplifying a double-bind in adherence to either Euro-American or Chinese cultural values. Findings elucidate the connections between sun-related behaviors and sociocultural backgrounds, especially how embracing Euro-American culture might increase sun exposure and sunburn tendency. Since sun exposure contributes to health outcomes (e.g., skin cancer, vitamin D status, and bone density), these findings have significant implications for public health prevention efforts.
AAPA statement on race and racism
Fuentes, A., Ackermann, R.R., Athreya, S., Bolnick, D., Lasisi, T., Lee, S.-H., McLean, S.-A., Nelson, R. (2019). AAPA Statement on Race and Racism. American Journal of Physical Anthropology, 169(3), 400-402. doi:10.1002/ajpa.23882
The AAPA Statement on Race and Racism was written by the AAPA subcommittee tasked with revising the previous AAPA statement on the Biological Aspects of Race that was published in the American Journal of Physical Anthropology, vol. 101, pp 569‐570, 1996. The Committee on Diversity (COD) subcommittee was comprised of (in alphabetical order): Rebecca Ackermann, Sheela Athreya, Deborah Bolnick, Agustín Fuentes (chair), Tina Lasisi, Sang‐Hee Lee, Shay‐Akil McLean, and Robin Nelson. The statement was unanimously accepted by the AAPA Executive Committee at its meeting on March 27, 2019 at the 88th Annual Meeting in Cleveland, Ohio and is available on the AAPA website at http://physanth.org/.
Practical and ethical considerations of using personal DNA tests with middle-school-aged learners
Wright, E.A., Wagner, J.K., Shriver, M.D., Fernandez, J.R., & Jablonski, N.G. (2019). Practical and ethical considerations of using personal DNA tests with middle-school-aged learners. The American Journal of Human Genetics, 104(2), 197-202. doi:10.1016/j.ajhg.2019.01.001
Wright, E.A., Wagner, J.K., Shriver, M.D., Fernandez, J.R., & Jablonski, N.G. (2019). Practical and ethical considerations of using personal DNA tests with middle-school-aged learners. The American Journal of Human Genetics, 104(2), 197-202. doi:10.1016/j.ajhg.2019.01.001
Shades of complexity: New perspectives on the evolution and genetic architecture of human skin
Quillen, E.E., Norton, H.L., Parra, E.J., Lona-Durazo, F., Ang, K.C., Illiescu, F.M., Pearson, L.N., Shriver, M.D., Lasisi, T., Gokcumen, O., Starr, I., Lin, Y.-L., Martin, A.R., & Jablonski, N. G. (2019). Shades of complexity: New perspectives on the evolution and genetic architecture of human skin. American Journal of Physical Anthropology, 168(S67), 4-26. doi:10.1002/ajpa.23737
Like many highly variable human traits, more than a dozen genes are known to contribute to the full range of skin color. However, the historical bias in favor of genetic studies in European and European‐derived populations has blinded us to the magnitude of pigmentation’s complexity. As deliberate efforts are being made to better characterize diverse global populations and new sequencing technologies, better measurement tools, functional assessments, predictive modeling, and ancient DNA analyses become more widely accessible, we are beginning to appreciate how limited our understanding of the genetic bases of human skin color have been. Novel variants in genes not previously linked to pigmentation have been identified and evidence is mounting that there are hundreds more variants yet to be found. Even for genes that have been exhaustively characterized in European populations like MC1R, OCA2, and SLC24A5, research in previously understudied groups is leading to a new appreciation of the degree to which genetic diversity, epistatic interactions, pleiotropy, admixture, global and local adaptation, and cultural practices operate in population‐specific ways to shape the genetic architecture of skin color. Furthermore, we are coming to terms with how factors like tanning response and barrier function may also have influenced selection on skin throughout human history. By examining how our knowledge of pigmentation genetics has shifted in the last decade, we can better appreciate how far we have come in understanding human diversity and the still long road ahead for understanding many complex human traits.
Sunscreen photoprotection and vitamin D status
Passeron, T., Bouillon, R., Callender, V., Cestari, T.L., Diepgen, T., Green, A.C., . . . Jablonski, N.G., & Young, A.R. (2019). Sunscreen photoprotection and vitamin D status. British Journal of Dermatology, 181(5), 916-931. doi:10.1111/bjd.17992
Global concern about vitamin D deficiency has fuelled debates on photoprotection and the importance of solar exposure to meet vitamin D requirements.
To review the published evidence to reach a consensus on the influence of photoprotection by sunscreens on vitamin D status, considering other relevant factors.
An international panel of 13 experts in endocrinology, dermatology, photobiology, epidemiology and biological anthropology reviewed the literature prior to a 1‐day meeting in June 2017, during which the evidence was discussed. Methods of assessment and determining factors of vitamin D status, and public health perspectives were examined and consequences of sun exposure and the effects of photoprotection were assessed.
A serum level of ≥ 50 nmol L−1 25(OH )D is a target for all individuals. Broad‐spectrum sunscreens that prevent erythema are unlikely to compromise vitamin D status in healthy populations. Vitamin D screening should be restricted to those at risk of hypovitaminosis, such as patients with photosensitivity disorders, who require rigorous photoprotection. Screening and supplementation are advised for this group.
Sunscreen use for daily and recreational photoprotection does not compromise vitamin D synthesis, even when applied under optimal conditions.
Variation in human hair ultrastructure among three biogeographic populations
Koch, S. L., Shriver, M. D., & Jablonski, N. G. (2019). Variation in human hair ultrastructure among three biogeographic populations. Journal of Structural Biology, 205(1), 60-66. doi:10.1016/j.jsb.2018.11.008
Human scalp hairs are often examined microscopically to study the variation and diversity among a range of visible morphological traits. In this study, we focused on the ultrastructure of human scalp hair within its keratinized matrix, emphasizing, the density and distribution of melanosomes, variation in cuticle thickness within populations, and the relationship of hair fiber ultrastructure with biogeographic ancestry. We used transmission electron microscopy (TEM) to visualize hair cross-sections and generate micron-scale resolution images for analysis of particle morphology and the layered hair matrix. Our results revealed considerable variation in all parameters examined, including the relationship of ultrastructure to biogeographic ancestry. Among the three metapopulations studied (European, African, and East Asian), we identified hair cross-sectional shape, cuticle dimensions, and melanosome distribution as traits that reveal statistically significant ancestry-related patterns. This study establishes trait patterns in hair morphology and ultrastructure among three biogeographically defined metapopulations to improve the current understanding of human variation in hair form and establish a foundation for future studies on the genetic and developmental bases of phenotypic variation in hair ultrastructure related to genotype.
Acute ultraviolet radiation exposure attenuates nitric oxide-mediated vasodilation in the cutaneous microvasculature of healthy humans
Wolf, S.T., Stanhewicz, A.E., Jablonski, N.G., & Kenney, W.L. (2018). Acute ultraviolet radiation exposure attenuates nitric oxide-mediated vasodilation in the cutaneous microvasculature of healthy humans. Journal of Applied Physiology, 125(4), 1232-1237. doi:10.1152/japplphysiol.00501.2018
Endothelial-derived nitric oxide (NO) contributes to normal healthy function of the human cutaneous microvasculature. Bioavailability of 5-methyltetrahydrofolate (5-MTHF) is important for the production of NO. Ultraviolet (UV) radiation exposure, specifically UVB, may deplete cutaneous 5-MTHF, thereby reducing NO-mediated microvascular function. Our findings suggest that acute UVB exposure attenuates NO-mediated vasodilation of the cutaneous microvasculature via degradation of 5-MTHF. These findings advance our understanding of the potential negative health impacts of acute UV exposure.
Focus on African diversity confirms complexity of skin pigmentation genetics
Lasisi, T., & Shriver, M. D. (2018). Focus on African diversity confirms complexity of skin pigmentation genetics. Genome Biology, 19(1), 13. doi:10.1186/s13059-018-1395-3
Renewed focus on African populations confirms the complexity of skin pigmentation genetics, and suggests future directions for pigmentation research.
Environmental selection during the last ice age on the mother-to-infant transmission of vitamin D and fatty acids through breast milk
Hlusko, L.J., Carlson, J.P., Chaplin, G., Elias, S.A., Hoffecker, J.F., Huffman, M., Jablonski, N.G., Monson, T.A., O’Rourke, D.H., Pilloud, M.A., & Scott, G.R. (2018). Environmental selection during the last ice age on the mother-to-infant transmission of vitamin D and fatty acids through breast milk. Proceedings of the National Academy of Sciences, 115(19), E4426-E4432. doi:10.1073/pnas.1711788115
Because of the ubiquitous adaptability of our material culture, some human populations have occupied extreme environments that intensified selection on existing genomic variation. By 32,000 years ago, people were living in Arctic Beringia, and during the Last Glacial Maximum (LGM; 28,000–18,000 y ago), they likely persisted in the Beringian refugium. Such high latitudes provide only very low levels of UV radiation, and can thereby lead to dangerously low levels of biosynthesized vitamin D. The physiological effects of vitamin D deficiency range from reduced dietary absorption of calcium to a compromised immune system and modified adipose tissue function. The ectodysplasin A receptor (EDAR) gene has a range of pleiotropic effects, including sweat gland density, incisor shoveling, and mammary gland ductal branching. The frequency of the human-specific EDAR V370A allele appears to be uniquely elevated in North and East Asian and New World populations due to a bout of positive selection likely to have occurred circa 20,000 y ago. The dental pleiotropic effects of this allele suggest an even higher occurrence among indigenous people in the Western Hemisphere before European colonization. We hypothesize that selection on EDAR V370A occurred in the Beringian refugium because it increases mammary ductal branching, and thereby may amplify the transfer of critical nutrients in vitamin D-deficient conditions to infants via mothers’ milk. This hypothesized selective context for EDAR V370A was likely intertwined with selection on the fatty acid desaturase (FADS) gene cluster because it is known to modulate lipid profiles transmitted to milk from a vitamin D-rich diet high in omega-3 fatty acids.
Egg white or sun-kissed: A cross-cultural exploration of skin color and women's leisure behavior
Chen, H.-Y., Yarnal, C., Chick, G., & Jablonski, N. (2018). Egg white or sun-kissed: A cross-cultural exploration of skin color and women’s leisure behavior. Sex Roles, 78, 255-271. doi:10.1007/s11199-017-0785-4
The present study explores how culture-based meanings and values toward skin color, which are associated with women’s body image ideals and gender-role expectations, profoundly influence women’s leisure behaviors. Using in-depth interviews with East Asian, Asian American, and Euro-American women (n = 43), results revealed how leisure behaviors are tied to cultural perceptions of skin color. People from different cultural backgrounds construct meanings and values pertaining to skin color, including beauty-related standards, social class, gender roles, and lifestyles. Culture-based values, such as the preference for tanned skin among Euro-Americans and for lighter skin among East Asians, affect a wide range of daily behaviors. These behaviors include conscious as well as subtle daily decision-making regarding sun-seeking, sun-avoidance, and sun-protection behaviors; indoor versus outdoor leisure participation; and appearance modifications. The study’s results add knowledge to how perceptions and attitudes toward skin color and appearance manifest in women’s daily behavior in general and leisure behavior in particular. In addition, the current study shows how individual behaviors reflect cultural meanings and values toward body image, specifically skin color, by emphasizing the links between cultural values and women’s day-to-day lives.
The biology of color
Cuthill, I.C., Allen, W.L., Arbuckle, K., Caspers, B., Chaplin, G., Hauber, M.E., . . . Caro, T. (2017). The biology of color. Science, 357(6350). doi:10.1126/science.aan0221
Animals live in a colorful world, but we rarely stop to think about how this color is produced and perceived, or how it evolved. Cuthill et al. review how color is used for social signals between individual animals and how it affects interactions with parasites, predators, and the physical environment. New approaches are elucidating aspects of animal coloration, from the requirements for complex cognition and perception mechanisms to the evolutionary dynamics surrounding its development and diversification.
The colours of humanity: The evolution of pigmentation in the human lineage
Jablonski, N. G., & Chaplin, G. (2017). The colours of humanity: The evolution of pigmentation in the human lineage. Philosophical Transactions of the Royal Society B: Biological Sciences, 372(1724). doi:10.1098/rstb.2016.0349
Humans are a colourful species of primate, with human skin, hair and eye coloration having been influenced by a great variety of evolutionary forces throughout prehistory. Functionally naked skin has been the physical interface between the physical environment and the human body for most of the history of the genus Homo, and hence skin coloration has been under intense natural selection. From an original condition of protective, dark, eumelanin-enriched coloration in early tropical-dwelling Homo and Homo sapiens, loss of melanin pigmentation occurred under natural selection as Homo sapiens dispersed into non-tropical latitudes of Africa and Eurasia. Genes responsible for skin, hair and eye coloration appear to have been affected significantly by population bottlenecks in the course of Homo sapiens dispersals. Because specific skin colour phenotypes can be created by different combinations of skin colour–associated genetic markers, loss of genetic variability due to genetic drift appears to have had negligible effects on the highly redundant genetic ‘palette’ for the skin colour. This does not appear to have been the case for hair and eye coloration, however, and these traits appear to have been more strongly influenced by genetic drift and, possibly, sexual selection. This article is part of the themed issue ‘Animal Coloration: Production, Perception, Function and Application’.
The anthropology of human scalp hair
Dadzie, O.E., Lasisi, T., & Jablonski, N.G. (2017). The anthropology of human scalp hair. In N. A. Vashi & H. I. Maibach (Eds.), Dermatoanthropology of Ethnic Skin and Hair (pp. 315-330). Cham: Springer International Publishing. doi:10.1007/978-3-319-53961-4_18
Hair is predominantly a proteinaceous fiber that originates from hair follicles located within the subcutis and/or dermis of the skin. It is one of the defining features of mammals, serving important functions, such as thermoregulation and endothermy. Among mammals, humans are exceptional in lacking a full covering of body hair. Instead the growth of terminal hairs is limited to specific body regions, such as the scalp, axillae, and groin. Our aim in this chapter is to provide an overview of the anthropology of human scalp hair. We will explore approaches to the study of variation in human scalp hair phenotypes, as well as the genetic and evolutionary basis of this diversity. The biology of human scalp hair, with emphasis on quantitative and qualitative differences among populations, as well as impact on hair grooming practices will also be discussed.
Youth violence: What we know and what we need to know
Bushman, B.J., Newman, K., Calvert, S.L., Downey, G., Dredze, M., Gottfredson, M., Jablonski, N.G., Masten, A.S., Morrill, C., Neill, D.B., Romer, D., Webster, D.W. (2016). Youth violence: What we know and what we need to know. American Psychologist, 71(1), 17-39. doi:10.1037/a0039687
School shootings tear the fabric of society. In the wake of a school shooting, parents, pediatricians, policymakers, politicians, and the public search for “the” cause of the shooting. But there is no single cause. The causes of school shootings are extremely complex. After the Sandy Hook Elementary School rampage shooting in Newtown, Connecticut, we wrote a report for the National Science Foundation on what is known and not known about youth violence. This article summarizes and updates that report. After distinguishing violent behavior from aggressive behavior, we describe the prevalence of gun violence in the United States and age-related risks for violence. We delineate important differences between violence in the context of rare rampage school shootings, and much more common urban street violence. Acts of violence are influenced by multiple factors, often acting together. We summarize evidence on some major risk factors and protective factors for youth violence, highlighting individual and contextual factors, which often interact. We consider new quantitative “data mining” procedures that can be used to predict youth violence perpetrated by groups and individuals, recognizing critical issues of privacy and ethical concerns that arise in the prediction of violence. We also discuss implications of the current evidence for reducing youth violence, and we offer suggestions for future research. We conclude by arguing that the prevention of youth violence should be a national priority.
Quantifying variation in human scalp hair fiber shape and pigmentation
Lasisi, T., Ito, S., Wakamatsu, K., & Shaw, C.N. (2016). Quantifying variation in human scalp hair fiber shape and pigmentation. American Journal of Physical Anthropology, 160(2), 341-352. doi:10.1002/ajpa.22971
This study aims to evaluate the use of quantitative methods of measuring variation in scalp hair fiber shape and pigmentation and carry out exploratory data analysis on a limited sample of individuals from diverse populations in order to inform future avenues of research for the evolution of modern human hair variation.
Cross-sectional area and shape and average curvature of scalp hair fibers were quantified using ImageJ. Pigmentation was analyzed using chemical methods estimating total melanin content through spectrophotometric methods, and eumelanin and pheomelanin content through HLPC analysis of melanin-specific degradation products.
The initial results reinforced findings from earlier, traditional studies. African and African Diaspora scalp hair was significantly curled, (East) Asian hair was significantly thick, and European hair was significantly lighter in color. However, pigmentation analyses revealed a high level of variability in the melanin content of non-European populations and analysis of curvature found a large range of variation in the average curvature of East African individuals.
Bugs R Us
The Edge 2016 Conversation – What do you consider the most interesting recent [scientific] news? What makes it important?
The Sepia Rainbow: The Fascinating Story of Human Skin
High-dose vitamin D3 reduces deficiency caused by low UVB exposure and limits HIV-1 replication in urban Southern Africans
Coussens, A.K., Naude, C.E., Goliath, R., Chaplin, G., Wilkinson, R.J., and Jablonski, N.G. (2015). High-dose vitamin D3 reduces deficiency caused by low UVB exposure and limits HIV-1 replication in urban Southern Africans. Proceedings of the National Academy of Sciences, 112(26), 8052-8057. doi: 10.1073/pnas.1500909112
Cape Town, South Africa, has a seasonal pattern of UVB radiation and a predominantly dark-skinned urban population who suffer high HIV-1 prevalence. This coexistent environmental and phenotypic scenario puts residents at risk for vitamin D deficiency, which may potentiate HIV-1 disease progression. We conducted a longitudinal study in two ethnically distinct groups of healthy young adults in Cape Town, supplemented with vitamin D3 in winter, to determine whether vitamin D status modifies the response to HIV-1 infection and to identify the major determinants of vitamin D status (UVB exposure, diet, pigmentation, and genetics). Vitamin D deficiency was observed in the majority of subjects in winter and in a proportion of individuals in summer, was highly correlated with UVB exposure, and was associated with greater HIV-1 replication in peripheral blood cells. High-dosage oral vitamin D3 supplementation attenuated HIV-1 replication, increased circulating leukocytes, and reversed winter-associated anemia. Vitamin D3 therefore presents as a low-cost supplementation to improve HIV-associated immunity.
The Site of Shuitangba (Yunnan, China) Preserves a Unique, Terminal Miocene Fauna
Jablonski, N.G., Su, D.F., Flynn, L.J., Ji, X., Deng, C., Kelley, J., Zhang, Y., Yin, J., You, Y., Yang, X. (2014). The site of Shuitangba (Yunnan, China) preserves a unique, Terminal Miocene fauna. Journal of Vertebrate Paleontology, 34(5), 1251-1257. doi: 10.1080/02724634.2014.843540
Skin Cancer Was Not a Potent Selective Force in the Evolution of Protective Pigmentation in Early Hominins
Jablonski, N.G., & Chaplin, G. (2014). Skin cancer was not a potent selective force in the evolution of protective pigmentation in early hominins. Proceedings of the Royal Society B: Biological Sciences, 281(1789). doi: 10.1098/rspb.2014.0517
Is There a Golden Mean for Sun Exposure?
Jablonski, N.G. (2014). Is there a golden mean for sun exposure? Journal of Internal Medicine, 276(1), 71-73. doi: 10.1111/joim.12248
The Role of Piloerection in Primate Thermoregulation
Chaplin, G., Jablonski, N.G., Sussman, R.W., & Kelley, E.A. (2014). The role of piloerection in primate thermoregulation. Folia Primatologica, 85(1), 1-17. doi: 10.1159/000355007
The insulating properties of the primate integument are influenced by many factors, including piloerection, which raises the hair and insulates the body by creating motionless air near the skin’s surface. The involuntary muscles that control piloerection, the musculi arrectores pilorum (MAP), are mostly absent except on the tail in most strepsirhines, and are entirely absent in tarsiers and some lorisids. The absence of piloerection and the reduced effectiveness of pilary insulation in preventing heat loss affected the evolution of behavior and metabolic thermoregulation in these animals. In lemurs, this situation contributed to the use of positional and social behaviors such as sunning and huddling that help maintain thermal homeostasis during day-night and seasonal temperature cycles. It also contributed in many lemurs and lorises to the evolution of a wide variety of activity patterns and energy-conserving metabolic patterns such as cathemerality, daily torpor, and hibernation. The absence of functional MAP in strepsirhines and tarsiers implies the absence of effective piloerection in early primates, and the reacquisition of whole-body MAP in ancestral anthropoids prior to the separation of platyrrhine and catarrhine lineages.
The Evolution of Skin Pigmentation and Hair Texture in People of African Ancestry
Jablonski, N.G., & Chaplin, G. (2014). The evolution of skin pigmentation and hair texture in people of African ancestry. Dermatologic Clinics, 32(2), 113-121. doi: http://dx.doi.org/10.1016/j.det.2013.11.003
- Variability in skin pigmentation phenotypes in African and African-admixed populations has not been well documented or genetically characterized.
- Afro-textured hair is a shared characteristic of most African and African-admixed people, and may represent an adaptation to protect the brain against thermal stress.
- Vitamin D deficiency is a risk for darkly pigmented people because of the natural sunscreening properties of eumelanin and the increased prevalence of indoor living.
- Use of race categories is ill-advised because of the genetic heterogeneity and socially constructed nature of races.
Juvenile Hominoid Cranium from the Terminal Miocene of Yunnan, China
Ji, X., Jablonski, N. G., et al. (2013). Juvenile hominoid cranium from the terminal Miocene of Yunnan, China. Chinese Science Bulletin, 58(31), 3771-3779. doi: 10.1007/s11434-013-6021-x
Fossil apes are known from several late Miocene localities in Yunnan Province, southwestern China, principally from Shihuiba (Lufeng) and the Yuanmou Basin, and represent three species of Lufengpithecus. They mostly comprise large samples of isolated teeth, but there are also several partial or complete adult crania from Shihuiba and a single juvenile cranium from Yuanmou. Here we describe a new, relatively complete and largely undistorted juvenile cranium from the terminal Miocene locality of Shuitangba, also in Yunnan. It is only the second ape juvenile cranium recovered from the Miocene of Eurasia and it is provisionally assigned to the species present at Shihuiba, Lufengpithecus lufengensis. Lufengpithecus has most often been linked to the extant orangutan, Pongo pygmaeus, but recent studies of the crania from Shihuiba and Yuanmou have demonstrated that this is unlikely. The new cranium reinforces the view that Lufengpithecus represents a distinct, late surviving lineage of large apes in the late Miocene of East Asia that does not appear to be closely affiliated with any extant ape lineage. It substantially increases knowledge of cranial morphology in Lufengpithecus and demonstrates that species of this genus represent a morphologically diverse radiation of apes, which is consistent with the dynamic tectonic and biotic milieu of southwestern China in the late Miocene.