This essay should be required reading for graduate students: “The problem with p-values”. David Colquhoun writes extensively about science and statistics, and in this essay he brings out many of the biggest misconceptions that drive poor conclusions in scientific practice.
Even quite respectable sources will tell you that the p-value is the probability that your observations occurred by chance. And that is plain wrong.
Paleoanthropology is one field in which papers that point out poor use of statistics are publishable. The primary fossil data are very sparse, and we work hard to establish what little we can say with confidence. There are generally scientists willing to criticize statistically misleading attempts to answer the unanswerable.
Personally, I’ve spent a good amount of time looking into the basic statistical underpinnings of human evolution datasets. For example, my paper “How much can cladistics tell us about early hominid relationships?” showed that the datasets of most hominin species are simply not big enough to yield confident conclusions about how they are related to each other. A later paper, “No brain expansion in Australopithecus boisei”, worked through statistical issues with time-series data on which paleoanthropologists have often based conclusions about trends in morphological features over time.
My all-time favorite paper outlining statistical problems in human evolution research is by Richard Smith, “Biology and body size in human evolution: statistical inference misapplied.” Smith shows a systematic problem with the most common comparisons of ancient human relatives. Now, twenty years after that paper was first published, most papers that consider body masses of fossil hominins still get this wrong.
That’s a well-worn tale in science. Pointing out statistical errors is sisyphean. Many recent papers in human evolution reflect poor statistical practice. And a good number of “classic” results are based on datasets that today would be statistically doubtful. Science is self-correcting, but it is going to take some hard work to get this stuff straight.
Hawks, J. (2004). How much can cladistics tell us about early hominid relationships?. American journal of physical anthropology, 125(3), 207-219. doi:10.1002/ajpa.10280
Hawks, J. (2011). No brain expansion in Australopithecus boisei. American journal of physical anthropology, 146(2), 155-160. doi:10.1002/ajpa.21420
Smith, R. J. (1996). Biology and body size in human evolution: statistical inference misapplied. Current Anthropology, 37(3), 451-481. JSTOR
"We realised nobody had directly compared Neanderthal [teeth loss] to modern humans, so we didn't realise Neanderthals had [slightly less] tooth loss," says Weaver.
This flies in the face of previous studies, which suggested that several Neanderthals lived long after losing all, or nearly all, their teeth.
But bizarrely, the finding that Neanderthals apparently had healthy teeth actually suggests something rather negative about them.
I don’t disagree that there is a slight difference in tooth loss. That does not contradict the real observation that some Neandertal individuals had extensive premortem tooth loss.
I agree that some people have made more cultural conclusions from the observation of tooth loss than the data warrant. I wrote about this back in 2005, when the subject of discussion was total premortem tooth loss in the Dmanisi skull D3444: “Caring for the edentulous”. My conclusions today don’t differ from then:
In the case of life history variation, I think that the survival of a small number of individuals under extraordinary circumstances says little about the habitual capabilities of a species.
A handful of Neandertals lived with fairly extensive loss of dental function, but that probably doesn’t tell us much about Neandertals that we do not already know about many primates.
What I really object to in the linked article is the way this topic is framed: This good thing about Neandertals “bizarrely suggests something negative about them.”
Often in human evolution, research is presented with a simple storyline that goes like this: “This bad thing everybody knows about, well, guess what—it’s actually good when you think about it from the evolutionary perspective.”
That’s the storyline of the sickle cell mutation. It causes disease, but it is an adaptation to malaria. It’s also the storyline of the “thrifty genotype” idea: Diabetes is bad, but its occurrence today may be a side effect of ancient adaptations to food scarcity.
That framing doesn’t erase the bad aspects of such biological traits, but it does give people a different way of thinking about why bad things happen. “Everything bad is actually good” is a fairly useful frame for teaching human evolution.
The opposite storyline is also pretty common. “That good thing that everybody knows about? Well, guess what—it’s actually bad when you think about it from the evolutionary perspective.”
This is how the invention of agriculture gets portrayed nowadays. Jared Diamond famously called it, “The worst mistake in the history of the human race.” The idea is that once upon a time, humans were adapted to a hunter-gatherer existence, and agricultural subsistence caused scores of bad unforeseen effects.
This “everything good is actually bad” storyline is especially common when it comes to studying Neandertals. For example, Neandertals seem to have eaten lots of meat. Does that mean they were successful hunters optimizing resources in a harsh environment? No, it means they failed to build knowledge of plant foods, putting them at extreme risk of extinction when times got tough.
Another example: Some Neandertal sites seem to have different assemblages of tools that may be suited to different functional tasks, for example some toolkits include many scrapers for preparing hides, while others lack such a dominance of scrapers. Is this evidence of clever and flexible Neandertals? No, to some archaeologists it was evidence that Neandertals must have behaved like herd animals, with women and children in some camps, and small groups of bachelor males in others.
Every so often, new evidence convincingly debunks one of these Neandertal stereotypes. For example, over the past ten years, a series of papers describing starches and phytoliths in Neandertal dental calculus have documented their use of plant resources, including cooking of some grains and the possible use of medicinal plants. In this case and many others, the press has reported the “surprising” conclusion that Neandertals were very much like modern human subsistence foragers.
Just once, I would like to see a journalist report such results as unsurprising evidence that past archaeologists were incompetent.
Now I don’t want to go overboard in the opposite direction. There probably really were some strange things about some Neandertals. Culture did evolve, and the evolutionary history of Neandertals probably yielded cultural abilities that humans lack, just as modern humans may have abilities that they lacked. In other words, I do not assume that they were merely modern humans with browridges.
But these are among the hardest ideas to test with archaeological evidence. At the same time, ideas about Neandertal cognitive difference align with persistent stereotypes about Neandertals. For that reason, I maintain an attitude of skepticism.
We know a good amount. Some of the cultural behaviors of recent and living modern humans have never been noted in Neandertal sites. But their tools, the traces of animals and plants that they ate, and their use of space show that Neandertal subsistence behavior had a lot in common with modern human subsistence foragers.
Many modern human subsistence foraging groups have left little or no evidence of “symbolic” artifacts, “complex site structure”, musical instruments, projectile weapons or similar trappings. We now know that Neandertals used pigments, engraved objects and rock surfaces, wore ornaments, made and used many kinds of bone tools, used shellfish, birds and small mammals—basically all things that past stereotypes held they didn’t do.
The point is, the difference between Neandertal and modern human behavior is clearly not a yawning chasm. They overlapped.
Studying Neandertal biological traits in combination with archaeology has a lot to offer to understanding their behavior. Dental pathology is a great avenue to understand how their health relates to their subsistence behavior. For example, Neandertals were once believed to have a much higher incidence of developmental dental pathologies than modern humans, traits like linear enamel hypoplasias that result from stress on the developing teeth from nutritional shortfalls or disease. It turns out that many modern human groups have just as high an incidence of such dental traits as Neandertals, including children from many agricultural groups.
Both Neandertals and prehistoric modern human subsistence foragers have vastly lower incidence of dental pathologies like caries when compared to most agricultural peoples, so it’s interesting to see that tooth loss was actually less among Neandertals than in the prehistoric modern human groups.
Better teeth may reflect the basic fact that Neandertals died faster than the Upper Paleolithic modern humans that followed them. By our best estimates (provided by Rachel Caspari and Sang-Hee Lee), Neandertal mortality was greater across the adult life span. Most known Neandertal dental remains come from relatively young adults, less than thirty or so years old.
Such high mortality probably does indicate something about Neandertal social relationships. Today’s human cultures owe much to the knowledge and experience of older adults, common in human societies. If those older adults were rarer, with some groups lacking older adults altogether, Neandertal cultures must have been poorer for it.
But adults in their twenties and thirties are not poor caregivers today. In fact, they are the primary caregivers toward both children and the most aged adults in our societies.
For that reason, I resist the framing that Neandertals good teeth may have meant they took less care of the sick. It may well have been true that sick Neandertals did not live as long, or have as good a chance of recovery. But I attribute that to the basic challenges of subsistence, not social incompetence.
Caspari, R., & Lee, S. H. (2004). Older age becomes common late in human evolution. Proceedings of the National Academy of Sciences of the United States of America, 101(30), 10895-10900. doi:10.1073/pnas.0402857101
Speth, J. (2004). News flash: negative evidence convicts Neanderthals of gross mental incompetence. World archaeology, 36(4), 519-526. doi:10.1080/0043824042000303692
Local villager Kongo Sakkae found some of the footprints prior to 2006, but the site didn’t reach scientists’ attention until 2008, when Pennsylvania-based conservationist Jim Brett happened to be staying at the Lake Natron Tented Camp, just a few hundred yards from the footprints.
Stunned by what he saw, Brett snapped as many pictures as he could and resolved to pass them along to a scientist he knew he could trust: Liutkus-Pierce, whom he had met when she was a postdoctoral researcher.
The trouble was, Brett picked the worst possible day to call.
“It was April Fool’s Day, I kid you not,” says Liutkus-Price. “He called me and said, ‘I think I have found some really cool hominid footprints.’ And I said, ‘Jim, can you call me tomorrow, so I know that this is not a joke?’”
The article gives a very nice account of the realization that these are fossil footprints, notes that they had been known to some local people earlier, discusses how collaborators were brought into the project, does not avoid mentioning a big problem with one of the researchers, and generally does a great job of showing how science is done.
Daniel Kahneman, who published Thinking, Fast and Slow nearly a decade after he won the Nobel Memorial Prize in Economics, went to almost heroic lengths to ensure that traditional academics would approve of his book. “It took me four years to write my book—four exceedingly miserable years because I was explicitly trying to do two things,” he says. “I wanted to write a popular book, without losing the respect of my colleagues. I paid a lot of money to have my book reviewed anonymously by young associate professors, four of them, I paid them two thousand dollars each, to tell me whether this would damage my reputation. And interestingly enough, it did damage my reputation among a subset of my colleagues.” Even so, Kahneman feels that the academic reaction to his book was by and large, very positive
I admire scientists like Kahneman who make the decision to reallocate their time toward public activities. By doing so, they advance the work of their colleagues and their field in general. His solution seems a little extreme, but I am glad to see how he values the referee work and the opinions of other scientific colleagues.
Interacting with the public is hard work. Being effective at public communication is a skill that scientists develop only through extensive practice, talking and writing honestly about the value of scientific work and its implications. Being an effective teacher is equally challenging, and while the skillsets do overlap, they are not identical.
I do a lot of public writing, blogging, documentary consulting, and filming. This work has made me a better scientist. I see the effects throughout my research. I make discoveries, and as much as possible, I get to take lots of other people with me. I don’t want to work any other way.
Most academics in my field have been totally supportive of the way I work. I do everything I can to promote the great work of friends and colleagues around the world. It’s always great to hear about connections made, and I’ve found so many friends in unexpected places.
I can’t deny that I’ve heard some criticism over the years. That kind of criticism is what stops many young scientists from even trying to engage outside their narrow subdiscipline. It’s entirely rational to keep your head down and stick to academic journal articles.
But honestly, most critical comments come from a small number of professionals who spend a lot of effort trying to become “academic celebrities” themselves. Some people assume that a certain degree of success in science will automatically cause people to listen to everything they say. The world doesn’t work that way, nor would anyone sensible want it to.
I’ve learned a lot from those interactions. I’m still finding out new ways to persuade people that our origins matter, to show them how our scientific work makes a difference.
Science News has a long feature article by Bruce Bower that recounts the new wave of examining hybridization in human origins: “Animal hybrids may hold clues to Neandertal-human interbreeding”. He features the symposium at the AAPA meetings this spring organized by Rebecca Ackermann, which involved many scientists researching hybridization in primates and other mammals.
The big idea is that the biological consequences of hybridization are often recognizable in the skeleton. Fossil human populations may include individuals with ancestry from diverse populations, like Neandertals and Denisovans, much more genetically different than any living populations are. Paleontologists might use insights from hybridization in other mammals to understand which fossils show evidence of such population mixture. The big success story is the Oase 1 mandible, which has a high proportion of Neandertal ancestry:
Since the fossil’s discovery in 2002, paleoanthropologist Erik Trinkaus of Washington University in St. Louis has argued that it displays signs of Neandertal influence, including a wide jaw and large teeth that get bigger toward the back of the mouth. In other ways, such as a distinct chin and narrow, high-set nose, a skull later found in Oase Cave looks more like that of a late Stone Age human than a Neandertal.
Roughly 6 to 9 percent of DNA extracted from the Romanian jaw comes from Neandertals, the team found.
“That study gave me great happiness,” Ackermann says. Genetic evidence of hybridization finally appeared in a fossil that had already been proposed as an example of what happened when humans dallied with Neandertals.
Not only does the Oase mandible have a high fraction of Neandertal ancestry, roughly 3 times higher than any living people today, but also that Neandertal-like DNA occurs in large chunks, indicating a recent Neandertal ancestry. This individual may have had a Neandertal great-great grandparent.
Such a recent potential Neandertal ancestor means that the population mixture in this real-life case is not too far from what occurs in some natural and laboratory experiments on hybridization. The models from the present day have great relevance to this past case.
I will add, the Oase individual is not a singular case. Many early Upper Paleolithic skeletal remains from Europe have comparable evidence of anatomical features that are common in Neandertals but very rare or absent in other populations. David Frayer has documented many of these in detail, joined by other scientists, especially Milford Wolpoff.
It just happens that Oase 1 is the first specimen with ancient DNA evidence showing substantially elevated Neandertal ancestry beyond that observed in later populations. The ‘Ust-Ishim femur does not have more Neandertal ancestry than recent humans, and although the value for Kostenki 14 is high, it is not an outlier. Both those specimens have Neandertal DNA in relatively longer linkage tracts than today’s people, allowing us to see that mixture had preceded the birth of these individuals by only 10,000–15,000 years or so. But Oase 1 was nearly on the scene; where this individual lived, population mixture was probably still underway.
We know from ancient DNA evidence of later specimens. The earlier Upper Paleolithic populations had more genetic influence from Neandertals than populations from the Mesolithic and later. In part, this reduction of Neandertal ancestry reflects natural selection against functional parts of the Neandertal genome; in part it probably reflects repeated immigration into Europe of people from West Asia or other parts of the world. A pattern that appears in morphological traits, with Neandertal resemblance declining over time in European Upper Paleolithic and later populations, is paralleled by genetics.
I am writing all of this because it’s hard to resolve a conflict when you don’t know what the other side wants. I honestly don’t know what those who are resistant to change want, but at least now they know what I want. I want to be in a field that prioritizes replicability over everything else. Maybe those who are resistant to change believe this too, and their resistance is about the means (e.g., public criticism) rather than the ends. Or maybe they don’t believe this, and think that concerns about replicability should take a back seat to something else. It would be helpful for those who are resistant to change to articulate their position. What do you want our field to prioritize, and why?
Simmons gives an example of his past work being shown false by non-replication in a vast sample, and makes some important points. Probably most salient, description of methods should allow other researchers to build on results.
Earlier this summer, Francis Thackeray published a short paper in the South African Journal of Science suggesting that lichens had deposited manganese upon the surfaces of hominin bone from the Dinaledi Chamber. Knowing that lichens depend upon light for their growth, Thackeray suggested that the Dinaledi bones had once been exposed to light for long enough to explain the lichen growth and manganese deposition.
Thackeray proposed that the geological evidence was somehow wrong, and that the Dinaledi Chamber had once been open to the surface. He elaborated on this view in an essay written for The Conversation:
I strongly believe that there was possibly a temporary entrance into the chamber, in addition to the one used by explorers today. This temporary entrance may been covered up by a rock fall that also trapped the individuals whose bones were found some time later.
Our team, including geologists and geochemists, has now published a response to Thackeray. We review some of the ways that manganese and other trace elements from dolomitic limestone can be deposited on fossil bone, and present additional evidence from the bone surfaces that rules out lichen involvement.
The Dinaledi bones bear traces of manganese and iron oxides. Some of the staining is dendritic, with very tiny features that suggest microbial involvement. The deposition process happens within sediment, in the dark
Several of the hominin fossils have linear tide marks of manganese or iron oxides. These mark an interface of air and sediment in which these bones were embedded.
Looking through a microscope, the bones bear many different patterns of mineral staining and calcite deposition. Some of the fossils have calcium carbonate deposition on top of manganese staining; others have manganese deposition on top of calcium carbonate. Some have successive encrustations of iron oxide, manganese, and iron oxide, as visible in this photo:
Additionally, some fossils have manganese deposits that have been removed by gastropod activity; others have manganese formed on top of old gastropod markings. All of this evidence is consistent with a long history of manganese and iron oxide deposition on the fossils within their current sedimentary environment.
None of this geochemical activity requires light.
One of the things that we have kept at the forefront of our papers describing the Rising Star cave system is that we must not set aside or ignore any of the geological evidence.
The geological evidence from the Dinaledi Chamber shows that it was an isolated depositional environment during and after the bones of Homo naledi entered the chamber. The sediments with the bones of H. naledi are very different in their chemical composition and particle characteristics from the neighboring Dragon’s Back Chamber. Dragon’s Back sediments have some input of surface material, the Dinaledi Chamber doesn’t. With articulated skeletal parts, complete representation of skeletons, and abundant fragile juvenile material, the bones of Homo naledi reject the hypothesis that the Dinaledi deposit could be a secondary accumulation from some other source. This is all compatible with the ceiling of the chamber, which is a chert layer with at most small thin fissures and no substantial openings, except for the vertical crack called the “Chute”.
Although the bone has been within the Dinaledi Chamber, that doesn’t mean it has been static. There has been erosion of the deposit since it began to form, with sediment and other material exiting the chamber through floor drains and some of the hominin bone being reworked along with the chamber’s surface. Bone within the Dinaledi Chamber was modified by gastropods and other cave-dwelling organisms, and minerals were deposited on its surfaces. The surfaces of many bones have been etched by the slightly acidic groundwater. Within parts of the deposit that are mere centimeters apart, the chemical circumstances differ.
Dirks, P. H., Berger, L. R., Roberts, E. M., Kramers, J. D., Hawks, J., Randolph-Quinney, P. S., ... & Schmid, P. (2015). Geological and taphonomic context for the new hominin species Homo naledi from the Dinaledi Chamber, South Africa. eLife, 4, e09561.
Dirks, P. H. G. M., Berger, L. R., Hawks, J., Randolph-Quinney, P. S., Backwell, L. R., & Roberts, E. M. (2016). Deliberate body disposal by hominins in the Dinaledi Chamber, Cradle of Humankind, South Africa?. Journal of human evolution 96: 149-153. doi:10.1016/j.jhevol.2016.04.007
Kruger, A., Randolph-Quinney, P. S., & Elliott, M. (2016). Multimodal spatial mapping and visualisation of Dinaledi Chamber and Rising Star Cave. South African Journal of Science, 112(5/6) doi:10.17159/sajs.2016/20160032
Randolph-Quinney, P. S., L. R. Backwell, L. R. Berger, J. Hawks, P. H. G. M Dirks, E. M. Roberts, G. Nhauro, J. Kramers. 2016. Response to Thackeray (2016) – The possibility of lichen growth on bones of Homo naledi: Were they exposed to light? South African Journal of Science doi:10.17159/sajs.2016/a0177
Thackeray, J. F. (2016). The possibility of lichen growth on bones of Homo naledi: Were they exposed to light?: scientific correspondence. South African Journal of Science, 112(7-8), 1-5. doi:10.17159/sajs.2016/a0167
Val, A. (2016). Deliberate body disposal by hominins in the Dinaledi Chamber, Cradle of Humankind, South Africa? Journal of Human Evolution 96: 145-148. doi:10.1016/j.jhevol.2016.02.004
The blackened hearths surround a spot where the jaw and six teeth of a Neanderthal toddler were found in the stony sediment. Puzzlingly, within each of these hearths was the horn or antler of a herbivore, apparently carefully placed there. In total, there were 30 horns from aurochs and bison as well as red deer antlers, and a rhino skull nearby.
Archaeologists believe the fires may have been lit as some sort of funeral ritual around where the toddler, known as the Lozoya Child, was placed around 38,000 to 42,000 years ago.
If that description is accurate, it is hard to imagine this behavior outside of a symbolic culture. This is more than simple mortuary deposition, it requires the construction of an elaborate and consistent series of associations with arbitrary objects.
Ewen Callaway reports on a talk at the European Society for Human Evolution meeting, presenting new human teeth from the ongoing Liang Bua archaeological work: “Human remains found in hobbit cave”. The story is that these remains may document some of the earliest modern human presence in the cave, postdating the last occurrence of H. floresiensis and extinct mammalian fauna. But I am always skeptical about the idea we can clearly diagnose the taxonomic status of unknown hominins from a couple of teeth.
María Martinón-Torres, a palaeoanthropologist at University College London who attended the talk, thinks that the lower molar looks like those of H. sapiens, whereas the premolar seems a bit more primitive. To prove conclusively that the teeth are human, she would like to see comparisons with a wide range of remains from H. sapiens and also from H. erectus (which might have survived in Indonesia until around 50,000 years ago). “I think they have quite a tough job. There are lot of factors to take into account,” she says.
It’s very encouraging that the cave still holds much more evidence to uncover, and I’m sure we’ll hear more as the work progresses.
The ongoing “replication crisis” in psychology has become an interesting study in the sociology of science. I don’t have anything especially deep to say about it, but I found this long update by the statistician Andrew Gelman very interesting: “What has happened down here is the winds have changed”. He focuses on a recent op-ed by Susan Fiske, who decries what she terms “mob rule” by other scientists who are questioning the statistical basis of some dearly-held theories in social psychology.
Gelman gives a history of the current “crisis”, pointing out that the statistical problems were apparent to some scientists in the 1960s. The current recognition of those problems has been long unfolding, and has yet to really change the practice of science. But it is raising uncomfortable questions for many established scientists who have built reputations on what many critics now describe as p-hacking. Fiske describes this criticism as “methodological terrorism”. The drama is ratcheting up.
I bring this up not in the spirit of gotcha, but rather to emphasize what a difficult position Fiske is in. She’s seeing her professional world collapsing—not at a personal level, I assume she’ll keep her title as the Eugene Higgins Professor of Psychology and Professor of Public Affairs at Princeton University for as long as she wants—but her work and the work of her friends and colleagues is being questioned in a way that no one could’ve imagined ten years ago. It’s scary, and it’s gotta be a lot easier for her to blame some unnamed “terrorists” than to confront the gaps in her own understanding of research methods.
To put it another way, Fiske and her friends and students followed a certain path which has given them fame, fortune, and acclaim. Question the path, and you question the legitimacy of all that came from it. And that can’t be pleasant.
Today’s established leaders attained their status under old rules that simply do not work for early and midcareer researchers today. Yet those established players have the power to allocate tenure, grants, and recognition, and they have mostly been relying upon the old rules to do so. As a result, early and midcareer scientists are justifiably frightened. They have to play the game by obsolete rules to get ahead, but it is increasingly clear that this game cannot lead to accurate and replicable science in the long term.
The best and most obvious way to make scientific progress is to tear down the nonreplicable edifice, but this inevitably requires attacking the cherished ideas of long-established players – many of whom have lucrative book and speaking careers based upon their social psychology “discoveries”.
And that’s why the authors’ claim that fixing the errors “does not change the conclusion of the paper” is both ridiculous and all too true. It’s ridiculous because one of the key claims is entirely based on a statistically significant p-value that is no longer there. But the claim is true because the real “conclusion of the paper” doesn’t depend on any of its details—all that matters is that there’s something, somewhere, that has p less than .05, because that’s enough to make publishable, promotable claims about “the pervasiveness and persistence of the elderly stereotype” or whatever else they want to publish that day.
When the authors protest that none of the errors really matter, it makes you realize that, in these projects, the data hardly matter at all.
What a mess.
The discovery of hominin fossils at Sterkfontein, South Africa, was eighty years ago this year. Recognizing the occasion, Jason Heaton, Travis Pickering and Dominic Stratford have a post on the Scientific American website: “The Fossil That Rewrote Human Prehistory”.
In August 1936, Robert Broom, a Scottish doctor with a keen interest in paleontology, visited a lime quarry in South Africa called Sterkfontein. In a guidebook at the time, the owner of the site, wrote, “Come to Sterkfontein and find the ‘missing link.’” It would not be long before Broom did just that.
It’s a nice short summary of the history of excavations at the site, which continues to produce new evidence about human origins.
[Annette MacLeod] examined the samples for the sleeping sickness parasites and found them in a handful of people, even though they showed no symptoms of the disease at the time. Further testing revealed that mice with parasites in their skin, but undetectable levels of the parasite in their blood, can easily transmit the disease to tsetse flies. Taken together, these results indicate that human skin is likely an “unappreciated reservoir of infection,” MacLeod and colleagues report this week in eLife. People who display no symptoms and have virtually no parasites in their bloodstream can still carry the disease and transmit it to others if they’re bitten by tsetse flies, she says. Skin-to-skin transmission between humans is technically possible, she adds, but is likely rare because it would have to get into broken skin.
The upshot is that if health agencies only test people’s blood for African sleeping sickness—the most common practice—they’re going to miss remnants of the disease that prevent it from being completely eradicated. “These asymptomatic people are the secret reservoirs that keep the disease going,” MacLeod says.
This makes a lot of sense. A reservoir in asymptomatic individuals, with long-term possibility of infecting new hosts, is an essential for human pathogens of the Pleistocene.
Classic Phillip Tobias:
During embryonic, foetal and post-natal life, the form of the calvaria becomes accurately moulded over the surface of the expanding brain. Pulsating, as the brain does with the beating of the heart, the outer surface of the brain imprints itself upon the interior of the brain case. In some areas, the convolutions or gyri leave hollow impressiones gyrorum on the endocranial surface, separated by areas where endocranial ossification has penetrated, to varying degrees, into the sulci between the gyri. With care, one may be able to read off from the surface of an endocranial cast some of the markings that had originally bedizenned the surface of the brain.
Yes, he really wrote “bedizzened.” Unfortunately in a context too long to tweet!
Tobias, P. V. (1987). The brain of Homo habilis: A new level of organization in cerebral evolution. Journal of Human Evolution, 16(7-8), 741-761.
Basal is a term that refers to the position of a node near the root of a phylogenetic tree. It’s a perfectly good term, it just doesn’t describe the branches that come from that node. To understand why, I find the following paragraph makes the problem with “basal” especially clear:
Every branching in a (phylogenetic) tree is rotatable (see Fig. 1). Of course, the tree has a base, and there is a most basal branching and a next most basal branching, but there is no such thing as the most basal clade. Because branchings are rotatable, there are always two most basal clades (if the most basal branching is completely resolved, Fig. 1) or even more most basal clades (if the most basal branching is not completely resolved, e.g. in Polyneoptera in Fig. 1). Both branches originating from a node (i.e. the two sister groups) are of equal age and have undergone equivalent evolutionary change. Whether a group has branched off early (basal) or later in the phylogeny contains no information about this particular group, but information about both this group and its sister group, because both branched off at the same time.
That is from an editorial from 2004 by Frank Krell and Peter Cranston in the journal Systematic Entomology, “Which side of the tree is more basal? Smith points to the editorial in her post, and I found this discussion helpful.
I’ve thought a good amount about this issue as I’ve been working on an undated assemblage. Reading the literature in this light, I am amazed at how often anthropologists cover up uncertainty about the relationships within Homo with the term “early Homo”. I admit to being guilty of using this term myself, it seems like such a convenient way to forget about all the problems applying species concepts.
Reading these articles about “basal” reminded me that “basal” is no substitute. Phylogeny doesn’t give us an easy way to refer to these lineages from deep time, and that is probably for the best. It’s important to keep our trees straight.
No one can write about the history of discoveries of these “famous” hominin specimens without taking note of the absence of women from the history of paleaonthropology. This week, Pyne published an essay reflecting on this gendered history: “Writing About Fossils Found By Men”.
Interestingly, women who show up in early paleoanthropology generally come from different background disciplines than do their male counterparts. Women tended to come to paleoanthropology from archaeology or anthropology, rather than from anatomy or paleontology – sciences that were less about spectacular discoveries of “things” (fossils) and more about understanding processes. But those sorts of research questions are hard to canonize in a science’s historical mythos. The discovery of some really cool fossil, traditional science storytelling goes, is so much more exciting to read and write about.
Accordingly, the traditional histories of paleoanthropology don’t have a whole lot of women in them. Dart’s student, Josephine Salmons, occasionally makes an appearance. Lady Smith Woodward shows up here and there in various stories of the Piltdown hoax, since her husband Sir Arthur Smith Woodward was so involved in Piltdown’s excavation and study. By and large, however, these women are ladies in the early fossil stories, not scientists. The big names in anthropological research, like Mary Leakey or Jacquetta Hawkes, tend to be researchers who focus more on the behaviors associated with early Homo than finding new hominin fossils. And this is pretty much the canon of paleoanthropology’s history of science as it currently stands.
As Pyne reflects on these famous fossils, she suggests that it is the “celebrity” nature of the fossils that tends to push women out of the story.
I found Pyne’s mention of Jacquetta Hawkes interesting in this context. Hawkes is not typically discussed in histories of paleoanthropology, because most of her work concerned the archaeology of the last few thousand years. In that area, she was a towering figure in the mid-twentieth century. But Hawkes herself did fieldwork as a student with Dorothy Garrod, and drew inspiration that set her on the path toward a career in archaeology (as discussed by the University of Bradford).
A skeleton of a Neanderthal woman was found, named Tabun 1 from the cave in which she was discovered. Jacquetta felt a strange kinship with this ancestral figure whose fragile skull she held. Despite their very different minds and experiences, both were part of the same stream of consciousness, “two atoms” in the millennial growth of the human brain.
Dorothy Garrod directed excavations that resulted in some of the epochal discoveries in the origin of modern humans and their interactions with the Neandertals. She didn’t make Pyne’s list because the Skhul and Tabun skeletal remains don’t fit her criteria of a single, “celebrity” skeleton. But that series of discoveries was much more important to the theoretical development of the field than most of the “celebrity” fossils.
If we consider the Skhul and Tabun discoveries, there’s no question that Garrod belongs in the pantheon of major fieldworkers in human origins. The Tabun archaeological sequence forms the basis for understanding the chronology of the Levant, with evidence for a quarter-million years of human habitation. To this we can add the excavation at Devil’s Tower, Gibraltar, and the Neandertal specimen it uncovered. Many archaeologists working today are frustrated with Garrod because her excavation methods left many unanswerable questions. Today no one would excavate a site like Tabun in the way that Garrod did. But this is true of almost every historical figure in the field.
Probably others would be more critical of Garrod than I am. I view her as one of the first prehistoric archaeologists to supervise massively interdisciplinary research. As she put it in her inaugural lecture as Disney Professor at Cambridge,
The prehistory of the Old Stone Age is far more closely bound up with certain branches of natural science—geology, palaeontology, palaeobotany—and the formation of a prehistorian in this sense calls for a scientific discipline to which the later stages of Man's story is not normally submitted.
It is noteworthy that among those who have built up the study of Early Man nearly all the outstanding names belong to men who have approached it from one or other of the natural sciences. This recruitment is to be expected in a subject which touches those sciences at so many points, and it has been of the highest value in the development and systematisation of human palaeontology in the widest sense. On the strictly archaeological side, however—that is, in the study of artefacts of fossil man—it has had certain results which are perhaps not quite so happy. It is time, I think, that these tendencies should be critically examined, and that we should ask ourselves whether they are not in part responsible for the present divorce between the student of the Old Stone Age and the archaeologist in the popular sense of the word.
With these words she introduced why archaeological knowledge is essential to understanding prehistory. Natural scientists, in her view, tended to treat artifacts as if they themselves were fossils, evolving under the laws of evolution, complete with hybridization and mutation. This in her view was wrong, leading to an exaggerated and typological view of cultural traditions. She was speaking to archaeologists about the importance of the archaeological approach.
As I read her, Garrod fully appreciated the role of different scientific disciplines in their own proper spheres, all of which had to be appreciated by the prehistorian. Certainly she followed that approach in her management of the excavation and study of material, in which she was strikingly modern in comparison to her scientific contemporaries. Like all modern discoveries of any importance, the Mount Carmel work in the 1920s and 1930s was a large-scale project that relied upon many collaborators. Theodore McCown, still a PhD student at the time, had responsibility for excavating the Skhul skeletons and transporting them to the U.K., where he worked to prepare them under the supervision of Arthur Keith. The resulting anatomical interpretation was one of the most important monographic descriptions of any fossil hominin sample, which faced up to the challenge of how to understand “transitional” patterns of anatomical features. It’s probably not an accident that Garrod, herself the daughter of a named professor of medicine, knew how to effectively work with experts in this area for this part of the work.
Thinking about McCown and Keith, they both influenced the interpretation of the fossils in such a way as to downplay their potential as “celebrity” fossils, notwithstanding Jacquetta Hawkes writing poems about the Tabun skeleton. Had Keith realized that the Skhul fossils were among were the earliest modern humans outside Africa, he might have created a mythos for Skhul V, but on this he missed the boat. Instead, he conceived them as transitional between earlier humans with more modern anatomy and later Neandertals. For his part, McCown refused to see the fossils as representatives a “type”, insisting that each was a mere sample of diversity within a population. The resulting description broke ground in how to conceive of variation in fossil human populations. Their science was a landmark, and the fossils did not take on mythological status in the process. I count that a scientific success.
I should point out that one consistent aspect of Garrod’s work is that her publications and reports all appeared “promptly” (as Jane Smith put it in a short biography). She was able to accomplish much, because she was effective in describing the science.
I don’t know how much Garrod’s approach to directing interdisciplinary work might have influenced Louis Leakey, who knew her. Looking at Leakey’s record it is clear that he conceived his and Mary’s roles differently than other earlier workers other than Garrod. The way that he recruited and delegated anatomical work to Phillip Tobias, John Napier, and other anatomical experts is reminiscent of how Garrod organized the Mount Carmel work. Maybe he would have taken this approach in any event.
At any rate, these are just a few of my thoughts. This seems like a fertile area for a historian to explore in more detail.