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john hawks weblog

paleoanthropology, genetics and evolution

Photo Credit: Rainy day at Amud Cave, Israel. John Hawks CC-BY-NC-ND

Link: Science blogs back!

Nature this week has a nice feature article on blogging in science, by Eryn Brown and Chris Woolston: “Why science blogging still matters”.

This marks my fifteenth year of blogging, and so I obviously think it’s worthwhile. I think the process of blogging is a lot like science itself – there are many ways to accomplish something, there are many more very smart people than there are obvious opportunities, and to be a real success, you have to find ways to do things that other people wouldn’t think of.

Of course, sometimes that just means persevering!

The survey uncovered some telling attitudes towards blogs and other forms of science outreach. Nearly two-thirds of respondents said that a lack of time was a ‘great obstacle’ to any sort of science communication.
But almost 70% agreed that communicating science can help to advance a researcher’s career, and nearly 90% said that it could help to recruit more bright minds to science.

I don’t think that blogs are especially good for reaching new audiences who do not already care about science. Blogs can be very good for helping already-interested people keep in the loop about new developments in a specialized area.

What I’ve noticed over the last few years is that a lot of professionals are now writing brief comments on new scientific work on Facebook, and linking to news articles, etc. And that has really yielded a “dumbing down” of commentary. Mainstream reporting on human evolution has actually gotten a lot worse in the last few years.

I’ve been happy to see a number of researchers in the last year or so publishing “blog posts” about their research findings on The Conversation. That’s a nice outlet enabling researchers to share their ideas directly, and gives a much better context for research findings than most media articles. What I’m a bit dismayed by is that these posts do not get shared very often on Facebook and other social media.

A trip to Israel, presenting about 'Time'

I’ll be in Israel this week to present a lecture for a symposium of the Israel Academy of Sciences and Humanities. The theme of the symposium is, “Time”, and I’ll be reflecting the deep time of human origins and evolution.

I’m excited about this presentation. Over the last two years, our field has seen an array of new discoveries that have changed the way we think about the origins of living people from mostly African ancestors. To me, right now, the most critical area where we know the story was complex, and badly need new data and models to understand that complexity, is around 250,000 to 350,000 years ago.

It was then that our modern human ancestors in Africa began to differentiate from an initially small population into branches that still exist in different regions of Africa today. It is now clear that many other hominin populations existed at the same time, including Homo naledi and some archaic forms of humans in Africa, Neandertals, Denisovans, and possibly other archaic humans in Eurasia, Homo floresiensis in Flores (and maybe others). In Africa, in Europe, and in Asia, some ancient populations experimented with, and ultimately adopted, new stone tool forms.

The big questions of human evolution all now cause us to focus upon this time interval for answers. How did culture influence our evolutionary pathway? How did ancestral hominins become modern humans? How did these hominin populations fit into their environment in ways that enabled them to survive and coexist?

I don’t have answers to these questions, but I now think that this critical time period is where we must look. I’ll be reflecting the big questions and the data that lead us to examine this time in my lecture.

Link: 'Myths of Human Genetics'

As the semester is getting rolling, and I am teaching Mendelian genetics in two courses this week, I want to link again to the invaluable “Myths of Human Genetics” website, from John McDonald at the University of Delaware.

McDonald has collated a series of human traits that have been used, at one time or another, to teach Mendelian inheritance in humans. None of them are Mendelian traits in reality, and many of them are demonstrably non-genetic in their etiology.

Some traits, such as tongue rolling, were originally described as fitting a simple genetic model, but later research revealed them to be more complicated. Other traits were shown from the very beginning to not fit the simple genetic model, but somehow textbook authors decided to ignore this. A quick search in the standard reference on human genetics, Online Mendelian Inheritance in Man (OMIM), makes it clear that most of these traits do not fit the simple genetic model. It is an embarrassment to the field of biology education that textbooks and lab manuals continue to perpetuate these myths.

Tongue rolling, hitchhiker’s thumb, asparagus urine – they’re all there, along with many references and citations to studies that show what scientists actually know about their inheritance.

I’m introducing students to a few more anthroposcopic traits than usual this semester, and it’s interesting what they come in already “knowing” about the inheritance of various traits. Thanks, High School Biology!

Link: The beauty of invasive species

Proceedings of the National Academy of Sciences is running an article by Carolyn Beans that profiles the work of Ellie Irons: “Science and Culture: Painting with invasive pigments”. Irons is a painter who has chosen to feature the pigment products of invasive plants in her work.

About one quarter of the weeds in Irons’ color palette are native to the northeastern United States. The rest are introduced, often highly invasive plants—some of which the city is actively working to eradicate from forested areas. Such efforts are undertaken for good reason; invasive species spread can devastate an ecosystem.
But Irons believes urban ecosystems are different. After all, many native plants couldn’t survive the harsh conditions. Where native plants fail, hardy weedy plants, she reasons, can step up to provide a wealth of ecosystem services—from stabilizing soil and reducing nutrient and stormwater runoff to cooling the air and providing food and habitat for animals.
Two Meadows, by Ellie Irons. Featured by Ecological Society of America
"Two Meadows Paintings", by Ellie Irons. Featured by the Ecological Society of America on Flickr. An installation of her work was exhibited at the ESA annual meeting in 2017. </figure> There are no "pure" ecosystems in the world, all have changed over time. But the pace of human change has posed unique challenges to some species and opportunities to others. It is for us to learn and recognize the workings of the world around us, to understand how we may best survive in the future.

What explains mtDNA introgression among archaic human populations?

In case anyone still wonders how variation in mitochondria might have been important to Neandertals and other archaic humans:

A bizarre find: Tiny powerhouses in your cells run at 122 degrees
The researchers grew human kidney cells and skin cells in petri dishes, which they kept at 38 degrees Celsius. Into these cells the scientists inserted a new type of fluorescent dye, which brightens as it cools. When the mitochondria became active, the fluorescence dimmed. This indicated that the temperature within the mitochondria rose between seven and 12 degrees Celsius, or an average of 10 degrees, as reported in the journal PLOS Biology on Thursday.

Previous researchers have suspected that human variation in mtDNA might relate to the tradeoff of heat production and ATP efficiency in mitochondria, with advantages for some mtDNA haplogroups in cold-adapted human populations. Circumstantial evidence for this hypothesis has been known for more than a decade, and I wrote about it back in 2005: “Mitochondrial DNA adaptations in living human populations”.

Even if important differences in mitochondrial function exist between human populations, mitochondrial DNA may not be the cause. Most of the genes that influence mitochondrial function are encoded in the nuclear genome, not the mtDNA. Yet some of the genes on the mtDNA do influence mtDNA function in ways that may have been selected in humans. Also, the mtDNA is the only part of the eukaryotic genetic complement that must function inside the mitochondrion itself, exposing it to a distinctive intracellular environment with its own possible effects on transcription.

The story of mtDNA in archaic humans has become more and more intricate. The earliest-known members of the Neandertal lineage, from Sima de los Huesos, Spain, have an ancient haplogroup that has not been found in later Neandertals or modern humans. This clade has been identified in Denisovans, although the variants in the Denisovan individuals known so far are fairly distant from the chronologically earlier Sima de los Huesos individuals.

Meanwhile, later Neandertals share a mtDNA clade that connects them more closely to the common mtDNA ancestor of modern humans, including all living African and non-African people. The origin of this clade is not known. It may have originated in Africa and have been exchanged into Neandertals by introgression some 250,000 years ago or more. Alternatively, it may have originated elsewhere and introgressed into both African and Neandertal populations. The extensive introgression of this mtDNA variant, in the absence of strong evidence of nuclear genome introgression at the same time, suggests that natural selection may have driven the mtDNA introgression.

No living people have been found with a mtDNA haplotype within the variation found within either the Neandertals or the Denisovans. Instead, everyone living today belongs to a subclade that originated within the last 300,000 years.

It is not currently clear whether this mitochondrial Eve lived before the populations that gave rise to all modern humans began to differentiate from each other. That differentiation began before 300,000 years ago, according to recent studies of African genetic variation from the nuclear genome. That’s earlier than most estimates of the date of the common mtDNA ancestor.

Within Africans today is much more mtDNA clade diversity than outside Africa. Throughout the pre-Columbian populations of most of the world, all people have mtDNA sequences that belong to two narrow branches of the mtDNA tree, which seem to have originated in the last 100,000 years. It is within these low-variation branches that a few functional variants have been found that might differentiate cold-climate populations from others. The adaptive story that has been examined so far for mtDNA does not relate to the much greater mtDNA variation that still exists within sub-Saharan African peoples.

I’ve been interested in mtDNA selection for a long time, and wrote about it in a 2006 paper: “Selection on mitochondrial DNA and the Neanderthal problem”.

There is a lot left to learn, which will no doubt leave today’s knowledge looking pretty inadequate. But what seems like mtDNA total replacement within Neandertals was a pretty striking event, and deserves more consideration as a possible case of adaptive evolution.

Is it meaningful if geneticists find that marriage can be influenced by genes?

The power of gene-trait association studies has increased markedly over the last few years. Samples of hundreds of thousands of individuals with genotype and phenotype data are coming online.

This statistical power has opened the door to discovering genes that have very small but significant effects on traits. In the process, a good fraction of what was once called “missing heritability” has actually turned up. Rare genes of medium effect, and common genes of incredibly tiny effect both matter to some extent.

Geneticists have started to ask a simple question: If most genes that affect a trait have incredibly tiny effects, are we discovering anything biologically interesting?

For many years, human geneticists have argued for larger and larger studies of gene-trait associations based upon the idea that genes will highlight biological networks. Any one gene might have a small effect, but finding many genes will allow geneticists to understand the inner workings of biology.

For some traits, that has proven not to be the case. Hundreds of genes, each with very small effects, don’t fit into any coherent biological network. In some sense, these genetic associations reflect all the different aspects of physiology that can influence human growth, metabolism, and behavior.

Behavioral traits seem to fit into this model, which has been dubbed the omnigenic model, in a recent paper Evan Boyle, Yang Li, and Jonathan Pritchard. Today it’s commonplace to see studies finding genetic associations for traits that are most salient in social psychology, identifying a few genes of fairly small effect for traits like “educational attainment”, or “age at birth of first offspring”.

Eric Turkheimer writes in the Genetics and Human Agency Project blog: “Why marital status is heritable.

It is only in the weakest (softest!) possible sense that you can refer to these genes as “genes for” the phenotype, or as “causal variants” for a phenotype, because they don’t actually have anything to do with the phenotype, with divorce, per se. The are cellular level body size effects, or appearance effects, or impulsivity, or alcohol or ginger hair effects, and even listing them like that probably makes their effects much more discrete and concrete than they actually are. If I had to guess most of the genetic action is at the cellular level, so causally distant from how you feel after a fight with your spouse that there is no point in even talking about it.
Heritability in and of itself has no particular relevance to questions about whether things like intelligence or divorce are biological as opposed to social constructions. Social constructions are heritable.

The main idea of Turkheimer’s post is that heritability by itself does not tell us that biology (as opposed to social phenomena) is relevant to explaining a trait. That is, correlation is not causation, and a genetic explanation for a trait that involves tiny influences of hundreds of genes is not a meaningful explanation.

And yet, I’m not very satisfied by this example.

Turkheimer has chosen the example of marriage status precisely because we are meant to assume that any important causal explanations must be totally psychological and social. Surely it is absurd to suggest that genes have any causally important role in such a social institution.

In some sense Turkheimer appears obviously correct. “Marriage status” in the United States or Europe in the early 21st century is an absurdly specific phenotype. It didn’t exist in our evolutionary past, and our genes could not possibly have adapted to it. Right?

But widen the frame a bit. Long-term pair bonding is exactly the kind of thing that mattered to natural selection during human evolution.

Look at another trait that is a major component of fitness: “age at birth of first offspring”. Some individuals have children very early in their adult lives, and others only have children much later. The proximate causes of these behavioral outcomes are unquestionably social and psychological. Yet age at first birth is heritable in populations today, and a number of genes found to explain small fractions of the additive component of variation in large samples of people. The trait is also quite strongly selected within the human populations where it has been examined. On average, women who have given birth to their first child earlier in their lives also have more children over their life spans.

How can this be? It would seem like trait that is so strongly correlated with lifetime reproductive success should have very little additive genetic variance in a population that has been at equilibrium with its environment for a long time.

Humans, of course, have not been anywhere near equilibrium recently. Our environment, both cultural and physical, has changed radically during the last 50,000 years, and continues to change rapidly even now. “Marriage” is a social institution that means something different today than it did 50 years ago. Marriage has different participation rates by age in today’s United States than in many other countries, and different rates in comparison to the recent past. Sure, it is reputed as one of the most stable institutions in human societies, but its psychological and social dimensions nonetheless can change rapidly.

In that sense, heritability of marriage status as a trait does have at least one salient biological explanation. Some genetic factors might correlate with marriage status in today’s populations precisely because the genetic differences that exist today are those that persisted in past social and physical environments, which were in some ways different from today’s environment.

There’s nothing trivial about noting that today’s social environments are markedly different from the past, and that by itself is a biological fact that influences gene-trait associations.

Link: Looking at the Misliya Cave maxilla

Bruce Bower last week had a nice article about the new Misliya Cave dating in Science News: “An ancient jaw pushes humans’ African departure back in time”.

The story in a nutshell is that a demi-maxilla from Misliya has been placed between 177,000 and 194,000 years ago. The teeth lack any close similarity with Neandertal teeth and are modern in size, and the morphology of the bone doesn’t resemble European Neandertals. That makes it indistinguishable from the cranial material from Qafzeh and Skhul, which are only between 90,000 and 110,000 years old. Up to double their age, the Misliya maxilla could be the earliest modern human outside Africa.

But I’m not so sure:

Hawks isn’t so sure the jaw belongs to H. sapiens. Interbreeding between H. sapiens, Neandertals and perhaps other Homo species in the Middle East could have produced a hybrid Misliya population characterized by humanlike jaws connected to bulkier, Neandertal-style bodies, Hawks says.
Or a Homo species closely related to H. sapiens — but not known from any previous fossils — may have traveled to Misliya Cave, he speculates. “This new discovery from Misliya Cave raises more questions than answers,” Hawks says.

I’m writing more on the implications of this discovery in the context of other recent work. There is a major change underway in how we understand “out of Africa”. I don’t think the traditional framing of “out of Africa” is very effective anymore, as leaving Africa is a tiny event, repeated many times over the last several hundred thousand years.

In the context of other discoveries, I think that “modern human” has lost much of the meaning it may once have had.

The big questions concern what was happening inside Africa, where many genetically diverse populations existed and interacted. How many ancestral populations gave rise to the growing population of modern humans after 100,000 years ago? How many African-derived people were involved in mixture with Neandertals 250,000 years ago, or 120,000 years ago? Did African-derived humans make it to China, or to Java, before 100,000 years ago?

Those are open questions, with some evidence pointing toward faster, more widespread dispersal, more mixture, and repeated genetic replacements.

Link: Searching for knotweed and other early North American domesticates

Annalee Newitz has written an article about Natalie Mueller’s search for the ancient food crops of North America: “Hunting for the ancient lost farms of North America”.

Over 2,000 years ago in North America, indigenous people domesticated plants that are now part of our everyday diets, such as squashes and sunflowers. But they also bred crops that have since returned to the wild. These include erect knotweed (not to be confused with its invasive cousin, Asian knotweed), goosefoot, little barley, marsh elder, and maygrass. We haven’t simply lost a few plant strains: an entire cuisine with its own kinds of flavors and baked goods has simply disappeared.

The article focuses upon the case of erect knotweed, but the others are worth comment also. The biological experimentation of ancient people was impressive, and in North America, the spread of maize farming reduced or eliminated many early domesticates.

The archaeology of plants has become more and more important to our understanding of ancient peoples—before, during, and after the adoption of agriculture. It will be amazing to see whether these aborted domesticates have any genetic signs of the ancient human manipulation.

What I think is so neat about these plants is that they trace the complexity of information exchanges across a network of societies over more than a thousand years:

She had assumed, based on previous studies, that knotweed was domesticated in Illinois, possibly about 1,200 years ago. But then she spoke with a Kentucky museum curator who told her about a mysterious grave from the 2,000-year-old Hopewell culture, found stuffed with seeds.
Examining the seeds, Mueller identified them as domesticated erect knotweed. This find makes the plant’s domestication roughly a millennium older than previously thought. But given that these fruits probably came after generations of breeding by farmers, it hints at a much older date.

It will be astounding to have greater knowledge of these kinds of exchanges in both the Americas and in Eurasia and Africa.

Link: The underrated takin

This is a fun article on an underappreciated mammal: “Meet the Takin: The Largest Mammal You’ve Never Heard Of”.

The takin is adapted to its mountainous environment in Asia. While its range includes many countries – including parts of India, Bhutan and Myanmar – most naturalists and hard-core mammal watchers encounter the species in China. Strangely enough, there it shares its range with one of the most beloved and well-known of large mammals, the giant panda. In fact, one of the first documented instances of a giant panda eating meat is trail camera footage of one of the fuzzy critters noshing on a takin carcass.

The fossil record of takin in China goes back to the Pliocene, with a number of fossil representatives in the Pleistocene of central China.

Sexual harassment as research misconduct

Scientific American has issued an editorial bringing attention to the new policy by the American Geophysical Union that redefines scientific research misconduct to include sexual harassment and other sexual misconduct in scientific research: “Science Suffers from Harassment”.

A number of scientific societies have recently issued statements condemning sexual harassment and assault, along with guidelines for ethical behavior among their members. The AGU’s approach is stronger and more direct. It argues that harassment is as egregious as the big scientific sins of data fabrication, falsification and plagiarism. Members found guilty of sexual harassment may thus be banned from presenting at conferences or publishing their research in AGU-run scientific journals, among other consequences that would limit their participation in the field.

Some more perspective on this can be found in a recent post in which I link to the AGU in a broader story: “Link: How scientific societies are moving to combat sexual harassment”.

It seems to me that this kind of redefinition puts much more pressure on coauthors and research collaborators of those who have carried out sexual harassment and assault.

When scientists are found to have been plagiarists, or fabricated data, there are very few circumstances in which they are rehabilitated as valuable coauthors and collaborators to other scientists. In the past, when instances of sexual misconduct have been treated internally and quietly by institutions, those individuals have continued in collaborations and coauthorship, and have continued to present and publish research without any connection between the two.

The AGU has forged a connection, and that has to change the way people operate in collaborations. This will have far-reaching effects.

Why do bamboo lemurs have such a diversity of gut microbes?

North Carolina State University has put out a news article about some recent work by Erin McKenney, who is studying the gut microbiome of lemurs: “Can You Guess Which Species Has the Most Gut Microbes?”.

The article has some statistics I’d never seen before about microbial community diversity in these lemurs:

[B]ecause McKenney studies lemurs, she hadn’t really looked at the gut diversity data for unrelated species. So when she shared the bamboo lemur’s diversity numbers with her mentor, NC State applied ecology professor Rob Dunn, she was surprised to learn that bamboo lemurs are superlative: They are home to more types of gut microbes than any other animal in the world (that we know of).
Specifically, McKenney has identified an average of 13,816 different “operational taxonomic units” (OTUs) – or types of microbes – in captive bamboo lemurs.

That’s more than any other animal yet examined, and roughly 14 times more diversity than in humans—even human hunter-gatherers like the Hadza, whose microbiomes are more diverse than agricultural populations.

Bamboo lemur
Golden bamboo lemur. Photo by Brian Gratwicke via Flickr. CC-BY 2.0

Bamboo lemurs have an interesting diet, which includes an ability to tolerate a level of cyanide that would be extremely harmful for most other mammals, so that dietary ecology might be related to their microbial diversity. That’s a “just-so” explanation, and who knows what diet has to do with it?

I just think this is a really interesting question. What difference does it make to have a diverse microbiome? Why would some species vary so much from each other, even within an order (like Primates)? Is this just a series of historical accidents leading to great diversity in some creatures? Or is their evolutionary history shaped by creating microbial niches inside themselves?

Should people lay off social psychologists with unreplicable ideas?

Pardis Sabeti has written an op/ed for the Boston Globe addressing the scientific casualties of the “replication crisis” in social psychology: “For better science, call off the revolutionaries”.

After naming a number of psychologists whose work has come under criticism for overhyped claims and underpowered samples, she decries the level of public criticism that these scientists have received:

Good science requires a spirit of collaboration, not domination. The debate in social psychology involves some essential criticism of past scientific practice, but revolutions can also lead to a bandwagon effect, in which bullies pile on and bystanders fearfully turn a blind eye. Especially as more disagreements among researchers surface in social media rather than professional publications, there is an insidious temptation to mistake being critical for being right, and to subordinate humility and decency to a “gloating sense of ‘gotcha,’” as the journal Nature put it.
There is a better way forward: through evolution, not revolution.

Sabeti contrasts the current situation in social psychology with genomics. In her account, much work in human genetics came under similar criticism in the early 2000s for relying upon underpowered samples, finding gene-trait associations that didn’t satisfy rigorous statistical requirements.

According to Sabeti, human genetics did not take the path of strong public criticism of underpowered studies, or of vilification of the researchers trying to find gene-trait associations with too little data. Instead, human geneticists built upon the imperfect results, revising them as samples got better and technology accelerated.

But there are many additional reasons why human genetics in the early 2000s was different from social psychology today.

The Human Genome Project during the late 1990s presented an enormous series of challenges to mainstream academic human geneticists. Scientists in government and in universities, led at first by James Watson and later by Francis Collins, rose to collective action, racing with Craig Venter’s private Celera venture to complete a draft of the human genome.

In doing so, they established a pattern of work that was unprecedented in biological science—in the process, building new expectations and protocols for sharing data. These scientists forged a collective understanding of the “big challenges” facing human genetics in the next decade. This included the critical need greatly increase knowledge of variation across the genome, to bring additional populations into human genetic samples, and to increase understanding of the genetic architecture of traits, especially disease traits.

That project established a hierarchy of scientists recognized as leaders, embedded within or experienced working with NIH, DOE, and other major funders. Some became directors of newly-founded major research institutes, among the first creations of the burgeoning philanthropic and government funding that moved into genome sequencing.

Few fields of science have ever seen the increase in money, power, and prestige poured into human genetics during the early 2000s. It’s not accurate to say this was a world free of conflict. Many of the disagreements within the field were acrimonious, and theoretical paradigms like common disease/common variant provoked strong debates. But none of these really compared to the rivalry between the public HGP and Celera during the 1990s. Meanwhile, prestige within the field came from directing and coordinating the Big Science efforts. That enabled project leaders to cultivate early career talent and select the most promising ideas from young people.

By contrast, social psychology has relatively little funding and no “Big Science” project. The competition for prestige and attention is very different than in human genetics. Psychologists write popular books, pen op/eds, and give Ted talks.

It’s like the Wild West, compared to human genetics. And where genetics was in the middle of a huge technological shift enabling vastly larger samples and more data for less money, samples in social psychology have been getting more expensive over time, not cheaper.

It will take a shock to the academic system to change the culture in such fields, toward pre-registered studies, vastly larger samples, and open data approaches.

Making the Mesolithic population of Scandinavia

A short article in The Conversation by Jan Apel describes some new research from Mattias Jakobsson’s lab on the population mixture that gave rise to the Mesolithic people of Scandinavia: “Ancient DNA sheds light on the mysterious origins of the first Scandinavians”.

This contradiction between genetics and geography can only be explained by two main migrations into Scandinavia. It would have started with an initial pulse from the south – modern day Denmark and Germany – that took place just after 11,700 years ago. Then there would have been an additional migration from the northeast, following the Atlantic coast in northern Finland and Norway becoming free of ice.

I think this work is exciting. The retreat of the European ice sheet left an opportunity for ancestral hunter-gatherers to colonize Scandinavia. The genetic data show that even this very simple biogeographic setting nonetheless gave rise to a complex mixture of populations from multiple sources, over a few thousand years of time.

Later, the introduction of farming into the region led to its own complex series of genetic migrations and interactions.

I can’t wait until we have equivalent or larger samples of individuals from other parts of the world of the same age.

Reference

Günther T, Malmström H, Svensson EM, Omrak A, Sánchez-Quinto F, Kılınç GM, et al. (2018) Population genomics of Mesolithic Scandinavia: Investigating early postglacial migration routes and high-latitude adaptation. PLoS Biol 16(1): e2003703. https://doi.org/10.1371/journal.pbio.2003703

What's the deal with the Sahelanthropus femur?

The species most often named as the earliest evidence for human evolution is Sahelanthropus tchadensis. The species is known from a skull and several mandibular specimens, found in Chad in 2001 by a team led by the French scientist Michel Brunet. These fossils are thought to date to between 6 million and 7 million years ago, approximately the time that our branch of the primate family tree diverged from the ancestors of chimpanzees and gorillas.

It has been called a “missing link”. It undergirds our best current timeline of human origins. It has been claimed as the earliest evidence for upright posture and bipedal locomotion in our lineage.

But there’s a mystery about Sahelanthropus. Some scientists claim that a fossil femur was found with the skull, a femur that they say is unlikely to be from an upright-walking ape.

Nature News has just published an article by Ewen Callaway investigating this mystery: “Controversial femur could belong to ancient human relative”.

The occasion for the article is that two scientists, Roberto Macchiarelli and Aude Bergeret, attempted to present a talk describing this femur at the annual meeting of the Societé d’Anthropologie de Paris this month. The society rejected their abstract, which has triggered some professional criticism.

The fossil may belong to the earliest known hominin, the group that includes humans and their extinct relatives. Few people have had access to it, but two scientists who analysed the bone briefly in 2004 have prepared a preliminary description of it. They had hoped to present their analysis at the meeting, which is organized by the Anthropological Society of Paris and is taking place in Poitiers. But the proposal by Roberto Macchiarelli, a palaeoanthropologist at the University of Poitiers and France's National Museum of Natural History in Paris, and Aude Bergeret, director of the Museum of Natural History Victor-Brun in Montauban, France, was rejected by the conference organizers.

Look, I’ve been following and writing about this case for a long time. I have been a scientific critic of the interpretation that Sahelanthropus was an upright hominin. I don’t think the cranial or dental evidence is persuasive, and I was a coauthor of both a peer-reviewed paper and a comment on the original description.

If a femoral specimen was found with the Sahelanthropus cranial remains, it is important evidence. If the femur preserves anatomy that would test the hypothesis of upright posture or bipedal locomotion, no one should pretend that the evidence does not exist. Secrecy was ridiculous from the start, now it is inexcusable.

The femur was discussed in La Recherche in 2009, and I reviewed what had been made public at the time: Sahelanthropus: ‘The femur of Toumaï?’”

My post included photographs of the femur in question:

Purported primate femur found at TM 266
The primate femur found at the TM 266 locality, originally numbered TM 266-01-63. Photo credit: Aude Bergeret

As I wrote at the time, the photographs do not provide clear-cut evidence that this is a hominoid femur and I would not make any conclusion based on them myself. I assume that Macchiarelli and Bergeret, with the opportunity to examine the specimen, are confident in their conclusion and I have no reason to doubt them.

There have been several other strange irregularities with the interpretation of Sahelanthropus. Most have involved one of the scientists who assisted with the original research, Alain Beauvilain, who wrote several critical articles questioning the discovery’s context and date. I reviewed this record in 2009, after Beauvilain’s published claim that the fossils had been found in a secondary context disturbed by local people at some point in the past: Sahelanthropus: Did camelherders bury Toumaï facing Mecca?”.

I have no direct knowledge about any of the supposed irregularities. One of the claims, that a left molar was mistaken for a right, was renounced in a letter signed by 29 scientists external to the team, a singular case in the history of paleoanthropology.

But what amazes me is just how long this has all gone on. All of the critics could be silenced within hours by data and evidence. Instead, silence about these key fossils has reigned for fifteen years.

Callaway got no new details about this fossil. Nevertheless, his article changes the situation substantially.

For example, this passage raises serious questions about the quality of the research:

David Pilbeam, a palaeoanthropologist at Harvard University in Cambridge, Massachusetts, who was a co-author on the 2002 and 2005 papers describing Toumaï’s skull and jaw, says that he saw the femur briefly while visiting Brunet in Poitiers more than a decade ago, but that he is not involved in any analysis. “All I can recall is that it lacked ends and was very black,” he says.

The major thesis of these research papers was that the skull reflects upright posture. A possible femur is obviously relevant to this hypothesis. If a coauthor was in a position that prevented him from either examining this key evidence or getting answers about it, it is very troubling.

It is time for Nature’s editors to investigate. Nature published the original description of the Sahelanthropus fossils in 2002, and two 2005 papers providing analyses of the skull and descriptions of new mandibular fossils.

Now Nature’s news division has revealed the existence of the specimen, and has quoted senior scientists who say that it may not be a hominin. Can this go on any longer?

Link: Remembering a dinosaur dictionary

I really like this post from Matt Wedel, reminiscing about a book that made a big difference to his start on the path toward paleontology: The New Dinosaur Dictionary, Mark Hallett, and the best Christmas present ever”.

“By Mark Hallett.” I didn’t know who this Hallett guy was, but his art was all over the book, along with William Stout and some guy named Robert T. Bakker and a host of others who were exploding my conception of what paleo art could even be. Anyway, this Mark Hallett was someone to watch, not only because he got mentioned by name a lot, but because his art had a crisp quality that teetered on some hypercanny ridge between photorealism and scribbling. His sketches looked like they might just walk off the page.

It’s a nice reminder of how important art can be to scientists. The comments include other scientists remembering some other valuable books.