In living color: 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. Science , this issue p. eaan0221

Background Global concern about vitamin D deficiency has fuelled debates on photoprotection and the importance of solar exposure to meet vitamin D requirements. Objectives To review the published evidence to reach a consensus on the influence of photoprotection by sunscreens on vitamin D status, considering other relevant factors. Methods 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. Results 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. Conclusions Sunscreen use for daily and recreational photoprotection does not compromise vitamin D synthesis, even when applied under optimal conditions. What's already known about this topic? Knowledge of the relationship between solar exposure behaviour, sunscreen use and vitamin D is important for public health but there is confusion about optimal vitamin D status and the safest way to achieve this. Practical recommendations on the potential impact of daily and/or recreational sunscreens on vitamin D status are lacking for healthy people. What does this study add? Judicious use of daily broad‐spectrum sunscreens with high ultraviolet (UV) A protection will not compromise vitamin D status in healthy people. However, photoprotection strategies for patients with photosensitivity disorders that include high sun‐protection factor sunscreens with high UVA protection, along with protective clothing and shade‐seeking behaviour are likely to compromise vitamin D status. Screening for vitamin D status and supplementation are recommended in patients with photosensitivity disorders.

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.

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’.

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.