science

Race is absolutely a human invention

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Trump and his administration are actively dismantling our economy and democratic institutions. One of the most recent parts of this assault is an executive order issued last week, “Restoring Truth and Sanity to American History.” The title itself is Orwellian doublespeak since the order describes the rejection of truth and science, while it in fact aims to whitewash American history.

An entire section of the order is devoted to, “Saving our Smithsonian” Institution, the national complex of museums, education outreach programs, research facilities, and a large Zoo. The order singles out an exhibit at the American Art Museum because it, “promotes the view that race is not a biological reality but a social construct … ‘a human invention.'”

As noted in the New York Times, the exhibit displays many quotations from the Statement on Race & Racism published by the American Association of Biological Anthropologists a few years ago. The statement explains, “Humans are not divided biologically into distinct continental types or racial genetic clusters,” which I think gets at the fundamental misconception most Americans have about race. Whether uninformed or outright racist and malicious, many people conceive of race as an invisible, unchanging essence that determines an individual’s capacities and behaviors. In the olden days race was thought of as ancestral and ‘in the blood,’ but in the genomic age people began attributing racial essence to DNA. All of these biological data—from blood to whole genomes—for at least the past fifty fucking years have shown that, again, “Humans are not divided biologically into distinct continental types or racial genetic clusters.”

Now, some folks who call themselves “race realists” (you can’t spell “race realist” without “racist”) might point to scientific research about human genetic variation with graphs showing humans partitioned into statistically-inferred clusters corresponding roughly with geography. The problem that tends to arise from here is the over-interpretation this within-species variation. As Lewontin showed back in 1972, and subsequent studies have consistently confirmed with more and more data, the amount of genetic variation that distinguishes different populations is but a small proportion (less than 15%) of the overall variation within our species. What’s more, because this variation is scattered throughout all of our DNA, most of it should be “neutral” with regard to evolution, with little or no effect on how likely an individual is to survive or reproduce. Simply put, humans across the planet are more genetically similar than different, and the limited genetic differences between populations probably doesn’t really influence how they behave or what they are capable of. Even though geneticists have argued this for years, many Americans are still quick to over-interpret the biological significance of these minuscule genetic differences, often tragically so.

To the contrary, race as many people think of it today is a recent historical concept – a “Fatal Invention” as Dr. Dorothy Roberts explains in her 2012 book. This is the consensus among experts in both the natural and social sciences. Yet Trump’s executive order specifically rejects this well established knowledge that race is in fact “a human invention,” as the order quotes from the Smithsonian art exhibit. This is one of the many purposes of rejecting the science and claiming that race is a biological reality — it serves to naturalize social differences and social inequality. If you maintain that people’s qualities are genetically determined and that groups differ fundamentally in their inherited genetics, then you have justification for avoiding social interventions to racial (and other kinds of social) inequality. As Dr. Michael Blakey explained back in 1999, “Race is essentially a means of defining ethnic and social status groups as biological entities. … In a racist or White Supremacist society, such as the United States, this … will often become the basis for decisions about the allocation of social resources and the solutions to social problems.”

Trump and Musk are both known to harbor unscientific and racist views about genetics, and both have been associated with far right and often white supremacist groups. The recent executive order claims that by communicating the actual science of human variation and the history of racism in this country, the Smithsonian is “under the influence of a divisive, race-centered ideology.” But with this administration, every accusation is a confession. They are actively dismantling our institutions and efforts that aim to address and repair the damage from centuries of racism, in order to advance their own white supremacist agenda (see for example here, here, and here).

The hand of Homo naledi points to life before birth

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Homo naledi is one of my favorite extinct humans, in part because its impressive fossil record provides rare insights into patterns and process of growth and development. When researchers began recovering naledi fossils from Rising Star Cave 10 years ago, one of the coolest finds was this nearly complete hand skeleton. The individual bones were still articulated practically as they were in life so we know which bones belong to which fingers, allowing us grasp how dextrous this ancient human was. And since finger proportions are established before birth during embryonic development, we can see if Homo naledi bodies were assembled in ways more like us or other apes.

The “Hand 1” skeleton of Homo naledi, adapted from a figure by Kivell and colleagues (2015). Left shows the palm-side view while the middle shows the back of the hand. The inset (b) shows many of the palm and finger bones as they were found in situ in Rising Star Cave.

In a paper hot off the press (here), I teamed up with Dr. Tracy Kivell to analyze finger lengths of Homo naledi from the perspective of developmental biology. On the one hand, repeating structures such as teeth or the bones of a finger must be coordinated in their development, and scientists way smarter than me have come up with mathematical models predicting the relative sizes of these structures (for instance, teeth, digits, and more). On the other hand, the relative lengths of the second and fourth digits (pointer and ring fingers, respectively) are influenced by exposure to sex hormones during a narrow window in embryonic development: this ‘digit ratio’ tends to differ between mammalian males and females, and between primate species with different social systems.

So, Tracy and I examined the lengths of the three bones within the second digit (PP2, IP2, DP2) and of the first segment of the second and fourth digits (2P:4P) in Homo naledi, compared to published data for living and fossil primates (here and here). What did we find out?

Summary of our paper showing the finger segments analyzed (left), and graphs of the main results (right). The position of Homo naledi is highlighted by the blue star in each graph.

The first graph above compares the relative length of the first and last segments of the pointer finger across humans, apes, and fossil species. The dashed line shows where the data points are predicted to fall based on a theoretical model of development. There is a general separation between humans and the apes reflecting the fact that humans have a relatively long distal segment, which is important for precise grips when manipulating small objects. Fossil apes from millions of years ago and the 4.4 million year old hominin Ardipithecus are more like apes, while Homo naledi and more recent hominins are more like modern humans. Because both humans and apes fall close to the model predictions, this means the theoretical model does a good job of explaining how fingers develop. Because humans and apes differ from one another, this suggests a subtle ‘tweak’ to embryonic development may underlie the evolution of a precision grip in the human lineage, and that it occurred between the appearance of Ardipithecus and Homo.

The second graph compares the ‘digit ratio’ of the pointer and ring fingers from a handful of fossils with published ratios for humans and the other apes. Importantly, the digit ratio is high in gibbons (Hylobates) which usually form monogamous pair bonds, while the great apes (Pongo, Gorilla, Pan) are characterized by greater aggression and mating competition and have correspondingly lower digit ratios. Ever the bad primates, humans fall in between these two extremes. Most fossil apes and hominins have digit ratios within the range of overlap between the ape and human ratios, but Homo naledi has the highest ratio of all fossil hominins known, just above the human average. It has previously been suggested that humans’ higher ratio compared to earlier hominins may result from natural selection favoring less aggression and more cooperation recently in our evolution. If we can really extrapolate from digit proportions to behavior, this could mean Homo naledi was also less aggressive. This is consistent with the absence of healed skull fractures in the vast cranial sample (such skull injuries are common in much of the rest of the human fossil record).

You can see the amazing articulated Homo naledi hand skeleton for yourself on Morphosource. Its completeness reveals how handy Homo naledi was 300,000 years ago, and it can even shed light on the evolution of growth and development (and possibly social behavior) in the human lineage.

Krapina endocast update (open data & code)

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In the Summer of 2019 I worked with some great Vassar undergrads to make virtual endocasts and generate new brain size estimates for the Neandertals from the site of Krapina, which we then published in 2021 (discussed in this blog post). The virtual approach to endocast reconstruction uses 3D landmark-based geometric morphometrics methods, and so in the spirit of open science we also published all the landmark data used for the study (as well as a bunch of other fossil human brain size estimates) in the Zenodo repository (here).

Neandertal fossil specimens Krapina 3 (purple/green) and Krapina 6 (yellow/red) with preserved landmarks and virtually reconstructed endocasts.

Something major and global happened around that time — who can even remember what? — and so I never got around to posting R code to accompany the study. So, I’ve finally gotten around to adding some very basic code to the Zenodo entry (better late than never). The code simply reads in the landmarks, estimates missing data for fossils, and does some very basic shape analysis and visualization. It’s doesn’t get into all the nuts and bolts of our study, but it should be enough to help folks check our data or get started with shape analysis in R.

R code includes ways to visualize the landmark data. Left: Principal components analysis graph of endocast shape for humans (red) and Neandertals (blue). Right: Triangle meshes of the average human and Neandertal endocast shapes, viewed from the right, bottom, and back.

Original article
Cofran Z, Boone M, Petticord M. 2021. Virtually estimated endocranial volumes of the Krapina Neandertals. American Journal of Physical Anthropology 174: 117–128. (link)

Scientific Racism

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The site’s been quiet in 2017, with little time to blog on top of my regular professional responsibilities, and of course watching the fascist smoke rising from the garbage fire of our 45th presidential administration with horrified disbelief. At work, my two new classes are keeping me plenty busy, and their content is quite distinct – one is on the archaeological record of Central Asia, the other centers around Homo naledi to teach about fossils. But by complete accident, examples of scientific racism came up in the readings for each course last week.

scientific-racism

Scientific racism refers to using data or evidence from the biological and social sciences to support racist arguments, that one racial group is better or worse than another group; the groups of course, are culturally determined rather than empirically discrete biological entities. This evidence is often cherry-picked, misinterpreted, and/or outright weak. Nicolas’ Wade’s 2014 A Troublesome Inheritance is a recent example of such a work. The book’s racial claims amount to nothing more than handwaving, and so egregious is the misrepresentation of genetic evidence that nearly 150 of the world’s top geneticists signed a letter to the editor rebuking Wade for “misappropriation of research from our field to support arguments about differences among human societies.” Wade’s book has no place in scientific discourse, but then almost anyone can write a book as long as a publisher thinks it will sell.

In addition to the outright misrepresentation of scientific evidence to support racist arguments, another manifestation of scientific racism is the influence of cultural biases in the interpretation of empirical observations. This may be less malicious than the first example, but is equally dangerous as it more tacitly supports systemic and pervasive racism. And this brings us to my classes’ recent readings.

First was a reference to the “Movius Line” in a review of the Paleolithic record of Central Asia (Vishnyatsky 1999) for my prehistory class. Back in the 1940s Hallum Movius, archaeologist and amazing-name-haver, noticed a distinct geographic pattern in the distribution of early stone tool technology across the Old World: “hand-axes” could be found at sites across Africa and western Eurasia, while they were largely absent from East Asian sites, which were dominated by more basic stone tools.

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Movius’ illustration of the distribution of Early Paleolithic technologies. From Fig. 1 in Dennell (2015).

Robin Dennell (2016) provides a nice review of how Movius’ personal, culturally influenced perception of China colored his interpretation of this pattern. Movius read this archaeological evidence to mean that early East Asian humans were unable to create the more advanced technology of the west, a biological and cognitive deficiency resulting from cultural separation: “East Asia gives the impression of having acted (just as historical China and in sharp contrast with the Mediterranean world) as an isolated and self-sufficient area, closed to any major human migratory wave” (Movius 1941: 86, cited in Dennell 2015). Racial and cultural stereotypes about East Asia directly translated to his interpretation of an archaeological pattern.

This type of old school scientific racism also arose in a review of endocasts (Falk, 2014) for my Homo naledi class. Endocasts are negative impressions or casts of a space or cavity, and comprise the only direct evidence of what extinct animals’ brains looked like. So to see how the structure of the brain has changed over the course of human evolution, scientists can search for the impressions of important brain structures in fossil human endocasts. Falk (2014) reviews one of the most famous of these structures – the “lunate sulcus” – which was used as evidence for reorganization of the hominin brain for nearly 100 years. In the early 20th century, anatomist and anthropologist GE Smith (not GE Smith from the Saturday Night Live Band)  thought he’d identified the human homologue of a groove that in apes separates the parietal lobe from the visual cortex. In humans, however, this groove was positioned more toward the back of the brain, which Smith interpreted as an expansion of an area relating to advanced cognition.

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The back of the brain, viewed from the left, of a chimpanzee (left) and two humans, the red line illustrating the Affenspalte or lunate sulcus (Fig. 1 from Falk 2014, which was modified from Smith 1903). The middle one also might be a grumpy fish.

It turns out that the lunate sulcus does not actually exist in humans, as the grooves identified as such are not structurally or functionally the same as the lunate sulcus in apes (Allen et al., 2006). Nevertheless, given what Smith thought the lunate sulcus was, it’s tragic to read his interpretations of human variation: “resemblance to the Simian [ape] pattern… is not quite so obvious…. in European types of brain….” (Smith 1904: 437, quoted in Falk 2014). The human condition for this trait was for it to be located in the back, reflecting an expansion of the cognitive area in front of it, and this pattern was less pronounced, according to Smith, in non-European people’s brains. This interpretation reflects two traditions at the time: 1) to refer to racial ‘types,’ ignoring variation within and overlap between groups, as well as 2) the prevailing wisdom that Europeans were more intelligent or advanced than other geographical groups.

ResearchBlogging.orgAnecdotes such as these may seem like mere scientific and historical curios, but they should serve as important reminders both that science can be accidentally guided by cultural values, or intentionally used for malevolent ends. Misconceptions and errors of the past shouldn’t be erased, but rather touted so that we don’t repeat mistakes that can have major consequences in our not-so-post-racial society.

References

Allen JS, Bruss J, & Damasio H (2006). Looking for the lunate sulcus: a magnetic resonance imaging study in modern humans. The anatomical record. Part A, Discoveries in molecular, cellular, and evolutionary biology, 288 (8), 867-76 PMID: 16835937

Dennell, R. (2016). Life without the Movius Line: The structure of the East and Southeast Asian Early Palaeolithic Quaternary International, 400, 14-22 DOI: 10.1016/j.quaint.2015.09.001

Falk D (2014). Interpreting sulci on hominin endocasts: old hypotheses and new findings. Frontiers in human neuroscience, 8 PMID: 24822043

Vishnyatsky L (1999). The Paleolithic of Central Asia. Journal of World Prehistory, 13, 69-122.