Wandering in prehistory – Fellows’ seminar by Nina Jablonski

28 March 2023

“Skin colour cannot be used as a basis for any classification of people into types or races. It is a complete fallacy that has led to an incredible amount of human suffering. Every person everywhere should know the facts of skin-pigmentation evolution, the fallacy of colour-based races and hierarchies, and the health consequences of our modern life where we are increasingly out of touch with life under the sun and our potential to produce vitamin D. We need to put this in the brain of every child, and as long as I have a brain I will work on this,” said Nina Jablonski, Evan Pugh University Professor of Anthropology at Pennsylvania State University and permanent STIAS fellow. (Jablonski was co-convenor of the STIAS Effects-of-Race long-term project.)

STIAS Fellow Nina Jablonski presented her seminar on 23 March 2023

“This talk is about the wanderings of our ancestors and also my intellectual wanderings for the past 40 years,” explained Jablonski. “It’s about understanding the life ways of human ancestors we will never meet.”

Jablonski acknowledged her long-time collaborator and husband George Chaplin also of the Department of Anthropology at Pennsylvania State University and STIAS Visiting Scholar, specifically referring to their early work in which they used data from NASA – which measured ultraviolet radiation (UVR) at the earth’s surface – to form the basis of interrogating levels of UVR relative to human skin colour in their much-cited 2000 paper in the Journal of Human Evolution.

Pointing to the renaissance in understanding of human evolution in the past 50 years due to our ability to better study the evidence across many disciplines, Jablonski highlighted that how ancient humans migrated out of Africa has often been presented as a global journey “but it was not this – a journey implies that the destination is known in advance. It was not a deterministic process – it played out over tens of thousands of years and they didn’t know where they were going – they went in search of resources to stay alive and to have reproductive success”. Humans moved to follow the animal populations on which they depended, the movement of animals was dependent on the vegetation they needed for their survival, which, in turn, was affected by climate changes.

Let the sun shine in

“We were also naked for most of human prehistory, with our skin as the primary interface between our bodies and the environment, and properties of the skin – including its colour – have evolved to meet the diverse challenges of different solar regimes. We evolved under the sun – under high levels of solar radiation – which impacted on all aspects of our anatomy and physiology”.

“The earliest known sites of human habitation – all in Africa – dating from 2 to 6 million years ago, are in the tropics. We are a tropical primal lineage that evolved under intense tropical solar radiation.”

As early members of the genus Homo foraged and became more active we started to lose body hair to liberate more body heat through increased sweating.  We also started to develop darkly pigmented skin as protection against UVR.

As we lost hair we gained the pigment eumelanin, a natural sunscreen that regulates the penetration of UVR into the skin, protecting the body from some of the damage caused by UVR while simultaneously allowing enough to penetrate so that the hormone vitamin D can be made in the skin. Vitamin D is essential for the functioning of all organs and insufficiency leads to greater susceptibility to chronic disease including diabetes and cancer, and also to infectious diseases.

Darker pigmented skin also assisted in preventing the degradation of folates, known as vitamin B9 or folic acid, which are needed for rapid cell division, in particular, during sperm production and early embryo formation, and also for processes in the skin essential for temperature regulation – the dilation and constriction of small blood vessels.

And what about lighter pigmentation?

Jablonski described this as “not a simple story, but one about the adaptive importance of skin pigmentation relative to UVR”.  It’s about parallel processes of pigmentation and depigmentation, photosynthesis and photo protection.

As humans started to move out of Africa from about 60 to 80 000 years ago they moved into areas with different sun exposure. Moving into the Northern Hemisphere with its relatively sunless or only seasonally sunny climate with much lower UVR had enormous implications for human evolution and skin pigmentation.

“Lighter skin started evolving at a faster rate,” explained Jablonski. “There was evolving depigmentation. We lost pigmentation in the process of dispersal to make it possible to produce Vitamin D under low UV.”

But that was not all. “Only small populations moved at any one time – maybe a 100 to 200 people,” said Jablonski. “This led to isolated groups that were tiny genetic subsets of the larger population. Therefore genetic variation was lost – both in many visible and invisible traits including pigmentation.” So depigmentation was a result of movement (often chaotic and unplanned), into regions with less and more seasonal UVR, often involving small populations and loss of genetic variation. Natural selection and processes of adaptation created what Jablonski described as an “artist’s palette of depigmentation genes”.

And, over time the factors that influenced people’s abilities to move and live successfully in different places changed as people became better at buffering themselves against the environment through the use of shelters, body coverings, and new methods for obtaining, processing and storing foods.

Exploring the Vitamin D line

Turning to their current project, Jablonski indicated that they will aim to unpack in more detail how the ‘Vitamin D line’ and its impact on human potential to produce Vitamin D from sun exposure determined where people could go and settle, but also how they adapted and found biocultural solutions. This will include looking at populations far north of the Vitamin D line to try to understand how they stay healthy.

Total vitamin D availability is a combination of the amount we can get from UVR exposure and the amount we take in from diet. “We will be looking at how different groups made biocultural compromises, involving natural selection and the growth of technologies and economies built around the intake of vitamin-D rich foods,” explained Jablonski. “We see dramatic examples of these compromises in Circumpolar peoples – in Alaska, Northern Canada and Greenland. They have highly tannable skin to enable them to deal with reflected UVR from water and ice but also a traditional diet rich in vitamin-D sources – including marine mammals and caribou.”

“Examination of the nature of ‘landscapes of vitamin D availability’, gives us a new way of envisioning habitable environments because they account for how much vitamin D people could produce in the skin from available UVR and how much vitamin D they could realise from dietary sources where they lived. What we discover is that people have been increasingly reliant on cultural buffering and biocultural compromises to survive, especially in extreme environments, and that these compromises have been highly contingent and fragile.”

“Humans made it work through cultural-buffering techniques.”

All of which is important to understand as we consider our existence today – where most of us live under artificial light, with little or no sun exposure and where even traditional communities are moving away from traditional diets. “We live cossetted and buffered lives very different from those we lived in the ecosystems in which our ancestors evolved,” explained Jablonski. “We are not in great shape regarding vitamin D – with ’total vitamin D availability’ being limited indeed for most people because of modern lifestyles.”

In discussion, Jablonski was asked how her work on skin-colour evolution is accepted in her extensive outreach activities.

“People generally welcome information stripped of pejorative adjectives, nouns and verbs.  People like straight talk, logical, clear information.”

“The fallacious framework of racial difference became fossilised by the economic circumstances of the time,” she continued. “In the toxic hierarchies of the political and social agendas at the brink of the modern era, race was adopted as a framework for how the world was organised. The embroidery of this race concept was then carried forward to a hideous extent.”


Michelle Galloway: Part-time media officer at STIAS
Photograph: Ignus Dreyer

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