Race: Understanding Human Diversity - Part 2
Visualization of different conceptual models of race (from here)
In the previous post, I outlined the history of racial anthropology and explained what current research as to say about the diversity of humans. In brief, Homo sapiens is a monotypic species with great regional variation, but this variation cannot be quantified into discrete races and can only be understood clinally. There have not been very great geographical or biological barriers between populations and demes to have given rise to different subspecies. Genetically, humans were remarkably similar to each other, more similar than the members of other large mammalian groups are to each other. When quantified, the concept of biological race falls flat.
Still, that regional variation is important and cannot be ignored. What about the great range of skin colors, hair types, skull morphologies, and other features of our bodies? How can we explain all this, if we're so similar?
The following is a rundown of various physical and genetic traits that have been used over the centuries in attempts to classify races, and were viewed by some as essential markers of race. There has been a large body of modern research on these characteristics, as you will see below:
Skin Color
Map of Indigenous skin colors in relation to latitude, based on the work of anthropologist Renato Biasutti (Samuel, CC BY-SA 3.0)
Perhaps the most visible marker of race, skin pigmentation has been so important in delineating human groups that even today we speak of "white people" and "Black people" as if these are discrete categories with biological meaning behind them.
In the early days of modern research, anthropologists noticed a correlation between latitude & climate and the maps of Indigenous skin colors around the world. It was argued that skin color was an adaptive feature in response to ultraviolet radiation and how it affects vitamin D synthesis, the breakdown of folates, and other aspects of healthy functioning (Jablonski & Chaplin, 2000). African populations vary in dark skin-pigmentation and, so the hypothesis went, as one subset expanded into Eurasia from roughly ~80 thousand years ago they encountered new latitudes and environmental conditions unfamiliar to their continent of origin at the time. Dark skin protects from intense UV radiation but by doing so it prohibits essential production of vitamin D that is needed - for example - for aid in pregnancy and milk production. In regions where there is little UV radiation, then, humans evolved lighter skin pigmentation to allow for vital vitamin functions. As well, over time, females of all populations developed slightly lighter skin from males, ensuring more healthy pregnancies.
Seems simple enough, but further research has called into question some things in this model. For example, among African groups alone, skin pigmentation is highly diverse, and all the genes associated with lighter colors in, say, Europe and East Asia, not only originated in Africa but predate Homo sapiens by several hundred thousand years (Crawford, et al. 2017; Feng, et al. 2021). As well, for groups living in Australia or the Indian Subcontinent, they directly inherited their dark skin from Africa too and these variants also originated before our species evolved. Thus, the genomes of the small groups who left Africa ~80 KYA contained all the alleles for such vastly different skin colors within them, but those for lighter skins may not even have necessarily been selected for in response to new conditions. In a review by Andrea Hanel and Carsten Carlberg, ancient DNA recovered from the remains of Paleolithic and Neolithic (the old & new stone ages, respectively) Europeans shows that, up until the last 5,000 years or so, they were still primarily dark-skinned to some degree. How could this be if dark skin would inhibit certain health functions in the bitter-cold, low-UV landscapes of Ice Age Europe? It seems that there were adaptations to other proteins that managed to allowed humans to gain the vitamin D and folate-breakdowns necessary for life even if their skin couldn't do the job (Hanel & Carlberg, 2020).
It seems, then, that skin color is a very fluid and ever-shifting condition for our species. Ancestrally, the genus Homo varied in pigmentation as our bodies shifted from fur to thinner (but no less dense) hair on our practically naked bodies. There were many different alleles for both darker or lighter skin that fluctuated over tens of thousands of years. In fact, the lighter skin of modern Europeans and East Asians seem to have been remarkably recent developments; for Europeans within the last 5,000 years, for East Asians within the last 7,500 years (Zhang, et al. 2022). Paleoart depictions of Ice Age peoples in both these regions should, therefore, probably be more dark-skinned than is usually imagined.
On a related note, I found this article very enlightening in regards to the myth of "skin thickness" between "races".
Hair Color & Texture
Map of Indigenous hair colors (translated from ecologix, CC BY-SA 4.0)
So skin color seems to be related to natural selection. Research by Nina Jablonski and George Chaplin seem to indicate that hair color diversity has more to do with genetic drift than natural selection. This is a far more random process in which the genes in founding populations, which have split off from larger and more genetically-diverse groups, take root and spread widely among their descendants.
A look at the distribution of hair colors above is a case in point: ancestrally Homo sapiens appears to have had jet-black hair and this is our default condition, but over time as certain groups with hair-color mutations arose in parts of the world, those traits became more fixed (Jablonski & Chaplin, 2017). The more isolated some groups were, the more likely such highly-derived hair colors would remain, hence the red hair in certain Northern European peoples or the blond hair in Solomon Islanders, which are regulated by specific alleles. In fact, hair color can near accurately be predicted from genetic material because of how few genes regulate it (Branicki, et al. 2022). It should be noted, as well, that hair color as a trait can change within a person's lifetime (Kumar, et al. 2018).
Hair texture and fiber shape is highly reflective of historic human movements, with research on the morphology of hair in different human sample groups shows a greater diversity within African populations than elsewhere in the world (Franbourg, et al. 2003; Lasisi, et al. 2016). This is an area of active research in desparate need of better research tools (Lasisi, et al. 2021), but we have learned that hair texture does appear to be influenced by natural selection. The tight curly hair typical of many African populations statistically played the best role in reducing heat gain and water loss from intense solar radiation and may have been the ancestral condition for our species (Lasisi, et al. 2023).
Eye Color
Prehistoric spread of skin, hair, & eye colors in Western Eurasia, from Hanel & Carlberg, 2020
Both hair and eye color do not appear to correlate with geographic distribution nor levels of UV radiation, and seem to be better explained as products of genetic drift than strong natural selection (Jablonski & Chaplin, 2017). Dark brown eyes seem to have been the standard for the earliest members of our species, and as populations moved around the world, a select few mutations created the great host of different eye colors we see today (Hanel & Carlberg, 2020). In the earliest European groups, for example, a gene called OCA2 which codes for iris de-pigmentation is responsible for the blue-eyed condition, which, in turn, was shuffled as other groups entered Europe in successive years; the first agriculturalists to enter Europe from Southwest Asia, as one instance, introduced genes for brown eyes (Fu, et al. 2016).
Skull Shape
Principle Component Analysis (PCA) of a global sample size of human skulls, plotted by degrees of physical similarity (from Matsumura, et al. 2022)
The history of biological anthropology is full of research based on craniometry, or the study of skull morphology. Texts abound with descriptions and classifications of "dolichocephalic" and "brachycephalic" peoples and these were features used to define human races. At first glance it seems obvious that the shape of the skull would be key to "figuring out a person's race" but recent studies incorporated genetics and the fossil record have demonstrated that skull shape is only part of the story.
For starters, all living human skulls share more similarities with each other than they do to other extinct human species like Neanderthals, and as well, all living and fossil Homo sapiens skulls are more closely allied physically than they are to other humans (Relenthford, 2024). Previous attempts to find a million-year-old deep-ancestry for modern races within different fossils of Homo erectus have not stood the test of time, as the genetic signature of all living humans shows a significantly more recent ancestry than this.
Secondly, the genetics factors behind skull shape have been found to be highly complex. A recent 2023 paper found that the physiology of the cranial vault (the upper part of the skull which supports the brain) was supported by 30 different areas of the genome, and related primarily to health and development (Goovaerts, et al. 2023). Taken in full, the human cranium is underpinned by a significant amount of genetic variation that seems to be constrained in its ability to undergo evolutionary change by its connection to other genes which affect development (Martínez-Abadías, et al. 2009). That said, certain areas of the skull show more of a tendency to change and be inherited than others, like the nasal and orbital cavities and the cheek bones, and these seem to be related to environmental factors; for example, there is a marked level of evolutionary convergence in the skulls of peoples living in the freezing-cold north of Europe, North America, and Northeast Asia (Hubbe, et al. 2009). Likewise, nasal projection in certain human populations seems to be related to dry and humid conditions (Carey & Steegmann, 1981). Interestingly, the rise of agriculture in several parts of the world does not seem to have had as much of an affect on skull shape: when the skulls of foragers and farmers were compared in one study, the differences between them were significantly small and this may reflect the long pre-agricultural history of cooking, grinding, and pounding food that hunter-gatherers had first perfected over tens of thousands of years (Katz, et al. 2017).
Much like hair texture, skull shape shows a greater morphological variation within Africa, which decreases statistically the further away from the continent you go. This is to be expected, considering the recent ~80 KYA population expansion from Africa which involved successively less-genetically diverse groups the further away they migrated (Matsumura, et al. 2022; Cramon-Taubadel, 2014). Even so, as the PCA analysis above demonstrates, there is still a significant overlap in skull shape between different global populations.
Taken together, global research indicates that the total variation in skull morphology was dictated by neutral evolution (which confers no effects on reproductive fitness) while certain aspects of the skull like the nose and cheeks are affected by evolutionary adaptation to climate, and that this variation is easily inherited through genetic drift.
As a relevant aside, a 2002 study found an opposite correlation of genetic variation between craniometrics and skin color: "roughly 13% of the total diversity is among regions, 6% among local populations within regions, and 81% within local populations" for skull shape, "88% of total variation among regions, 3% among local populations within regions, and 9% within local populations" regarding skin color (Relenthford, 2002).
Dentition
Shovel vs non-shovel shaped incisors (edited from dozentist, CC BY-SA 4.0)
The human jaw does not appear to be affected by neutral evolution but instead is directly correlated to diet and the physical pressures of chewing (Harvati, et al. 2024). This is in direct contrast with the cranium, which as aforementioned showed little distinctions between foragers and farmers. Sexual dimorphism also plays a role in the shape of the mandible, once again demonstrating a human characteristic affected by multiple factors.
As far as teeth are concerned, they do appear to evolve neutrally and therefore can be linked to genetic mutations and specific population movements (Rathmaan, et al. 2023). This has led to some fascinating research regarding the historical clues left in human dentition in certain parts of the world, much of it through the work of biological anthropologists Richard Scott and Christy Turner.
Some populations in East Asia show a condition called sinodonty, where the back of their incisor teeth are shaped like shovels (see above). This trait has been traced back both genetically and in the archaeological record about 35 thousand years ago, and it appears to have been inherited by the ancestors of Amerindian peoples in a derived "hyper-sinodont" form. Other groups in Eastern Eurasia show sundadonty, which lacks shoveling, especially among Southeast Asians, Polynesians, and the historic Jōmon of Japan (Aboriginal Australians and the people of New Guinea show neither condition). These distinctions in dentition clearly are reflective of successive population movements in prehistory that can be detected in human remains:
"As with virtually all human biological variation, however, dental traits do not show presence/absence patterns that enable clear differentiation between biogeographic groups. Rather, we see varying degrees of affinity that support the inference that human biological variation exhibits a gradual change in trait frequencies across populations" (Scott, et al. 2023).
Blood Type
Splits and changes of red blood cell alleles over time between different human species (from Mazières, et al. 2025)
Red blood cell types have also historically been used in studies on race in the pre-genomic age. Recent research has focused more on DNA sequencing and full-scale genome sequencing, but in recent years interest as re-emerged on blood types.
The distribution of the A, B, and O blood types is best explained primarily through genetic drift and positive evolutionary selection (unlike neutral, positive selection confers beneficial reproductive success). Thus, when blood types are mapped onto the continents, there are very few exclusive correlations with human populations.
A recent 2025 study found evidence that the change in blood groups can be traced almost neatly to the recent Eurasian expansion of ~80 thousand years ago (Mazières, et al. 2025). Both Indigenous Africans and our nearest fossil relatives the Neanderthals and Denisovans share the same blood groups, pointing to an inherited trait from our common ancestor well beyond 400,000 years ago. As a few small groups emerged from Africa 80 KYA and experienced a rapid change in blood types in the millennia following this movement.
Genetic Traits Related to Diet & Health
Some traits discovered through genetic sequencing have been argued to be specific "racial markers" for certain groups. Given, at this point, we're trying to understand human diversity through the lense of a modern evolutionary understanding, it's better to look at these traits and markers as evidence of past adaptations and movements rather than as a "checklist" of traits for any one race.
Take, for example, variant 370A of the gene EDAR. This encodes for a protein responsible for the development of skin, hair, teeth, and sweat glands in the embryo. Around 35 thousand years ago, evidence of this variant change emerged in Eastern Eurasia and spread across the region by 19 thousand years ago, where it was subsequently picked up by both the ancestors of Native Americans and the early Polynesian wayfinders. In the descendants of all these groups, EDAR 370 A is associated with thick hair, an increase in the density of sweat glands, and sinodonty (Kamberov, et al. 2013; Mao, et al. 2021; Zhang, et al. 2022). Why did this trait emerge and spread so quickly during this time. Research is ongoing but it is notable that during the Last Ice Age East Eurasia experienced a significantly humid phase, so having thicker hair and a greater ability to sweat would have been beneficial for hunter-gatherers living in such a dry region.
Other traits are related to agricultural developments within the last 12 thousand years or so. For example, an allele variant of the gene ADH1B has been found to have emerged within East Asian groups that domesticated rice, which was often fermented into alcoholic beverages: though this process conferred nutritional benefits at the time, in recent centuries it has also been correlated with increased negative affects of alcohol consumption (Peng, et al. 2010). Lactase persistence - or the ability to drink milk into adulthood - has been shown to correlate with a deep history of cattle domestication and reliance on milk products. Contrary to the "whimsy" of certain white-supremacist groups, while lactase persistence is highly prevalant in European populations, it is also found widely in African and southern Eurasian groups (Itan, et al. 2010). Drinking milk as an adult doesn't make you "racially superior".
Another common misconception is that the "sickle-cells are a Black trait". In brief, sickle-cells are caused by a mutation that changes the shape of red blood cells from circles to crescent "sickle" shapes. This change goes some way towards the prevention of malaria as the Plasmodium parasite which causes it cannot survive for long in a sickle-celled blood stream. That said, in the modern age of increased lifespans, having sickle-cells for many years can lead to anemias and other diseases that destroy the body's ability to function. Recent genomic research has shown a single origin of the sickle-cell mutation as far back as 7,300 years ago to the Holocene Wet Phase, a period of humid, wetland conditions across the Sahara, Middle East, Southern Asia, and the Mediterranean (Shriner & Rotimi, 2018). This mutation subsequently spread across Africa and into Eurasia. So although it is true that people of African and African American descent show a high likelihood of having the sickle-cell mutation, specific cases of it merely correlate with areas that currently or historically harbor malaria parasites. South Asians, Greeks, Turks, Arabs, and other descendant populations can have the mutation too.
What about Intelligence?
I suppose a brief word must be said about IQ and intelligence.
A popular hot-button topic among academics and cranks alike is the question of whether human races differ cognitively. Much ink has been spilled on this topic - personally, I found Angela Saini's 2019 book Superior to handle the subject most completely & honestly - and there are obvious political stakes depending on who you ask.
Attempts have been made by some researchers to find specific genetic markers of intelligence, but have always come to dead-ends. Geneticist Bruce Lahn comes to mind: his work arguing that gene variants for brain size recently evolved in some human groups verses others have since failed to be replicated and debunked (Mekel-Bobrov, et al. 2007; Timpson, et al. 2007). Curiously, such individuals conducting such research always seem to have ulterior motivations.
Then there is the matter of IQ or intelligence quotients, which provide a score of cognitive intelligence based on specific tests. Previous IQ studies have been used to "prove" that certain human groups are smarter than others, but upon close examination what such IQ tests show says more about socio-political status and environmental health and stability than anything about "biological race". Poor and disenfranchised groups are often struggling with basic survival and nutrition, which affects brain health and development and thus shaped the IQ scores they may recieve. As well, IQ tests may say something about the ability of an individual to perform mathematical, scientific, or academic problems well, but will say nothing about a person's ability to perform socio-cultural or artistic functions: different "intelligences" are needed for each of these. In total, IQ gives only part of the status of an individual and betrays an ability to celebrate what makes each person whole and unique.
In any case, as the quote below from Hampshire, et al. 2012 beautifully spells out, a multitude of factors go into human intelligence, on genetic, environmental, nutritional, and social fronts. There is nothing specific in the brain in regards to intelligence that can be accurately measured and thus traced genetically through some human descent groups verses others.
In Summary
If this brief and in-exhaustive look at the modern science of human physical and genetic variation is a bit confusing, admittedly that is the point. In evolutionary biology - especially cladistics - we are so used to thinking of the acquisition of defining evolutionary traits as very straight forward. Tigers and house cats have retractable claws, but bears don't; tigers, house cats, and bears have shearing carnassial teeth, but horses don't; tigers, house cats, bears, and horses have a complex placenta, but wombats don't; and so on.
When studying human variation in the present and over time, we simply cannot look at traits in the same way. Physical traits that appear to be concrete like skin color, hair texture, and skull shape, are influenced by so many, often non-correlating factors, and our flexibility in adapting to new environments and interbreeding with each other means that such traits will never stay distinct within populations and demes for long.
Instead of thinking about human variation in terms of racial groups, which creates misleading simplistic binary models, it is better and more scientifically accurate to consider the totality of the data and understand human variation as the complex historic process is truly was.
And in the last part of this series, I hope to do just that and trace the origin and spread of Homo sapiens to where it stands today, showing a far more accurate way to understand human diversity.
Book References
Gavin Evans. Skin Deep: Dispelling the Science of Race (Oneworld Books, 2019)
Angela Saini. Superior: the Return of Race Science (Beacon Press, 2019)
G. Richard Scott & Christy G. Turner. The Anthropology of Modern Human Teeth (Cambridge University Press, 2000)
Paper & Article Citations
Wojciech Branicki, et al. 2011. Model-based prediction of human hair color using DNA variants (Human Genetics)
J W. Carey & A T. Steegmann Jr, 1981. Human nasal protrusion, latitude, and climate (American Journal of Physical Anthropology)
Noreen von Cramon-Taubadel, 2014. Evolutionary insights into global patterns of human cranial diversity: population history, climatic and dietary effects (Journal of Anthropological Sciences)
Nicholas G. Crawford, et al. 2017. Loci associated with skin pigmentation identified in African populations (Science)
Yuanqing Feng, et al. 2021. Evolutionary genetics of skin pigmentation in African populations (Human Molecular Genetics)
A. Franbourg, et al. 2003. Current Research on Ethnic Hair (J Am Acad Dermatol)
Qiaomei Fu, et al. 2016. The genetic history of Ice Age Europe (Nature)
Seppe Goovaerts, et al. 2023. Joint multi-ancestry and admixed GWAS reveals the complex genetics behind human cranial vault shape (Nature Communications)
Andrea Hanel & Carsten Carlberg, 2020. Skin colour and vitamin D: An update (Experimental Dermatology)
Katerina Harvati, et al. 2024. Comparative 3D Shape Analysis of the Iwo Eleru Mandible, Nigeria (PaleoAnthropology)
Mark Hubbe, et al. 2009. Climate Signatures in the Morphological Differentiation of Worldwide Modern Human Populations (The Anatomical Record)
Yuval Itan, et al. 2010. A worldwide correlation of lactase persistence phenotype and genotypes (BMC Evolutionary Biology)
Nina Jablonski & George Chaplin, 2017. The colours of humanity: the evolution of pigmentation in the human lineage (Philos Trans R Soc Lond B Biol Sci)
Nina Jablonski & George Chaplin, 2000. The evolution of human skin coloration (Journal of Human Evolution)
Yana G. Kamberov, et al. 2013. Modeling Recent Human Evolution in Mice by Expression of a Selected EDAR Variant (Cell)
David C. Katz, et al. 2017. Changes in human skull morphology across the agricultural transition are consistent with softer diets in preindustrial farming groups (PNAS)
Anagha Bangalore Kumar, et al. 2018. Premature Graying of Hair: Review with Updates (International Journal of Trichology)
Tina Lasisi, et al. 2023. Human scalp hair as a thermoregulatory adaptation (PNAS)
Tina Lasisi, et al. 2021. High-throughput phenotyping methods for quantifying hair fiber morphology (Nature Scientific Reports)
Tina Lasisi, et al. 2016. Quantifying variation in human scalp hair fiber shape and pigmentation (American Journal of Biological Anthropology)
Xiaowei Mao, et al. 2021. The deep population history of northern East Asia from the Late Pleistocene to the Holocene (Cell)
Neus Martínez-Abadías, et al. 2009. Heritability of human cranial dimensions: comparing the evolvability of different cranial regions (Journal of Anatomy)
Hirofumi Matsumura, et al. 2022. Global patterns of the cranial form of modern human populations described by analysis of a 3D surface homologous model (Nature Scientific Reports)
Stéphane Mazières, et al. 2025. Rapid change in red cell blood group systems after the main Out of Africa of Homo sapiens (Nature Scientific Reports)
N. Mekel-Bobrov, et al. 2007. The ongoing adaptive evolution of ASPM and Microcephalin is not explained by increased intelligence (Human Molecular Genetics)
Luca Pagani, et al. 2016. Genomic analyses inform on migration events during the peopling of Eurasia (Nature)
Yi Peng, et al. 2010. The ADH1B Arg47His polymorphism in East Asian populations and expansion of rice domestication in history (BMC Evolutionary Biology)
Frédéric B. Piel, et al. 2020. Global distribution of the sickle cell gene and geographical confirmation of the malaria hypothesis (Nature Communications)
Hannes Rathmann, et al. 2023. Inferring human neutral genetic variation from craniodental phenotypes (PNAS NEXUS)
John H. Relethford, 2023. Craniometric variation and the ancestry of modern humans (American Journal of Biological Anthropology)
John H. Relethford, 2002. Apportionment of global human genetic diversity based on craniometrics and skin color (American Journal of Physical Anthropology)
Jon Riddell, et al. 2020. Characterisation of a second gain of function EDAR variant, encoding EDAR380R, in East Asia (European Journal of Human Genetics)
Nakisa B. Sadeghi & Adewole S. Adamson, 2023. The Problematic Legacy of Skin-Thickness Measurement in Race-Based Dermatology Research (JAMA Dermatology)
G. Richard Scott, et al. 2023. Peopling of the Americas: A new approach to assessing dental morphological variation in Asian and Native American populations (American Journal of Biological Anthropology)
G. Richard Scott, et al. 2016. Sinodonty, Sundadonty, and the Beringian Standstill model: Issues of timing and migrations into the New World (Quaternary International)
Daniel Shriner & Charles N. Rotimi, 2018. Whole-Genome-Sequence-Based Haplotypes Reveal Single Origin of the Sickle Allele during the Holocene Wet Phase (The American Journal of Human Genetics)
Pontus Skoglund & Iain Mathieson, 2018. Ancient Genomics of Modern Humans: The First Decade (Annual Review of Genomics and Human Genetics)
Nicholas Timpson, et al. 2007. Comment on Papers by Evans et al. and Mekel-Bobrov et al. on Evidence for Positive Selection of MCPH1 and ASPM (Science)
Xiaoming Zhang, et al. 2022. A Late Pleistocene human genome from Southwest China (Current Biology)
