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paleoanthropology, genetics and evolution

Photo Credit: From the catwalk at Sterkfontein. John Hawks CC-BY-NC-ND

Stone tools now 3.3 million years old

Sonia Harmand presented a talk at the Paleoanthropology Society meeting this week describing her team’s discovery of stone tools in a 3.3-million-year-old context at Lomekwi, on the west side of Lake Turkana. Michael Balter reported on the talk in a story in Science: “World’s oldest stone tools discovered in Kenya”:

In 2011, Harmand’s team was seeking the site where a controversial human relative called Kenyanthropus platyops had been discovered in 1998. They took a wrong turn and stumbled upon another part of the area, called Lomekwi, near where Kenyanthropus had been found. The researchers spotted what Harmand called unmistakable stone tools on the surface of the sandy landscape and immediately launched a small excavation.

The story discusses the contents of the talk, that the tools have been found both from surface and excavation contexts. According to the article, the artifacts show quantitative differences from known Oldowan assemblages, all of which are at least 700,000 years more recent. These differences led Harmand and colleagues to name a new tradition, which they are calling the “Lomekwian”.

I can’t really comment more informatively about this until the work is published so that I can evaluate it. The obvious implication is that stone tools were invented and used by multiple lineages of early hominins. Just as there were different styles of body shape and bipedal mechanics among early hominins, there were likely different styles of technical traditions. A few of these were stone, but almost certainly there were perishable tool traditions among most populations of early hominins. Just taking what we know from living chimpanzee populations, with different traditions of tool use, complex tool sets made from perishable materials, and occasional use of durable objects made from stone. All hominins added initially was the deliberate flaking of stone to make objects recognizable in the archaeological record.

That is to say, humans have elaborated upon a technical ability that is latent among all the apes. This technical ability rests upon social learning skills that are necessary in chimpanzee societies, and early hominin societies inherited those skills from the common ancestors of humans and chimpanzees. After millions of years of exploring this technical space, some experiments led to the manufacture of stone flakes and choppers. Possibly one or more experiments led to the manufacture of bone points or piercers, as evidenced at Swartkrans and Kromdraai, and often attributed to robust australopithecines.

Such traditions may or may not have been shared across different hominin populations. In chimpanzees, technical traditions are not widely shared, yet we know that they may last locally for at least a few thousand years. If a chimpanzee-like model applied across the Pliocene, traditions that lasted a few thousand years across local areas would occasionally be visible to archaeologists, if they were looking for them.

Now they are.


Boston University’s research office has a nice article about Kristi Lewton’s research on pelvic biomechanics: “In defense of wide hips”. The piece refers to Lewton’s investigation of the “obstetrical dilemma”, the hypothesis that the demands of bipedalism for a shortened pelvis may have sharpened the constraint on gestation time in hominins because of the demands of birthing infants.

If the basic assumptions of the obstetric dilemma are right, says Lewton, participants with wider hips should run and walk less efficiently than those with narrow ones. But that wasn’t what Lewton and her team found. Instead, they found no connection at all between hip width and efficiency: wide-hipped runners moved just as well as their narrow-hipped peers. Lewton and her colleagues published their results in March 2015 in the online journal PLOS ONE. The work was supported by grants from the National Science Foundation and The Leakey Foundation.
“This ‘trade-off’ between hips wide enough for a big baby and small enough for efficient locomotion does not seem to occur,” says Lewton. “That means that we have to rewrite all of the anthropology textbooks! Even outside of textbooks, the general public thinks that if your hips are wide, you’re a bad biped, and that does not seem to be the case.”

The research paper discussed in the article is the recent one by Anna Warrener and colleagues, “A Wider Pelvis Does Not Increase Locomotor Cost in Humans, with Implications for the Evolution of Childbirth”.

Reference

Warrener AG, Lewton KL, Pontzer H, Lieberman DE (2015) A Wider Pelvis Does Not Increase Locomotor Cost in Humans, with Implications for the Evolution of Childbirth. PLoS ONE 10(3): e0118903. doi:10.1371/journal.pone.0118903


James Gorman of the New York Times has an article today about the long-term field research on hunting by the chimpanzees at Fongoli, Senegal.

The Fongoli chimps find the bush babies in their dens in trees. Chimps will stab and poke one of the small animals, sometimes wounding but not impaling it, until it comes out of its hiding place. The chimps will grab it, Dr. Pruetz said, and immediately “bite the head off.”
Females, even those with infants, and juvenile chimps can do this kind of hunting. The process does not put a premium on speed and strength as the chase does, so big males do not have an advantage. But there is more than technique and technology involved. There is social change.

Last year for my MOOC, I interviewed Jill Pruetz about her work at Fongoli. There are many interviews with her online, but this one really digs into the details of female hunting, the unique savanna setting of the Fongoli group, and the ways that chimpanzees use water in this seasonal environment.

It is a great interview, and like many of my other videos available on my YouTube channel.


Me: “So apparently today is the tenth anniversary of the first Eccleston episode.”

Gretchen: “Yeah, no, that was like two weeks ago.”

Sophie: “Don’t try to out-nerd us on this, Dad.”

Me: “I just saw it on somebody’s Facebook feed.”

Gretchen: “Um, hon, I follow Doctor Who on Facebook.”

Sophie: “Geez, Dad.”


Notable paper: Rangan H, Bell KL, Baum DA, Fowler R, McConvell P, et al. (2015) New Genetic and Linguistic Analyses Show Ancient Human Influence on Baobab Evolution and Distribution in Australia. PLoS ONE 10(4): e0119758. doi:10.1371/journal.pone.0119758

Synopsis: Rangan and colleagues investigate whether ancient Aboriginal Australian people were responsible for dispersing the boab tree (Adansonia gregorii) across its current geographic range in northwestern Australia. Although tree was not formally cultivated, its fruit has long been consumed by local people. The authors studied the pattern of gene flow in the tree’s phylogeography, finding it to be very similar to the pattern of loan words for the tree among Australian languages, suggesting that the practices of ancient people were responsible for the tree’s current distribution sometime after the Last Glacial Maximum.

Interesting because: Baobab species have been used by humans in Africa, Madagascar and Australia. Previous work has shown that African baobab distributions have been influenced by human agency, but people have assumed that ancient people weren’t involved in dispersal of the Australian species. The new result shows the extent that hunter-gatherers may have been intentionally dispersing useful plant species in Australia.

Link: The girl with baboon in her spine

New Scientist reports on a presentation at the Paleoanthropology Society meeting, in which Marc Meyer and Scott Williams describe one of the vertebral elements attributed to A.L. 288-1, the famous “Lucy” skeleton, as the vertebra of a gelada: “Baboon bone found in famous Lucy skeleton”.

One possible explanation was that the vertebra fragment came from a second, juvenile member of Lucy's species. So Williams and Meyer did a comparative study that included vertebrae from other Australopithecus fossils. To satisfy a personal hunch, Williams also added vertebrae from other animals known to have lived in the Hadar region 3.2 million years ago, such as porcupines and pigs. The results showed, surprisingly, that the fragment may not have belonged to Australopithecus at all.
"Baboons were a close match, both in shape and size," says Williams. "So we think we've solved this mystery. It seems that a fossil gelada baboon thoracic vertebra washed or was otherwise transported in the mix of Lucy's remains."

Mistakes in field identification of fossil remains are inevitable. It is rare for such misidentifications to persist for long under laboratory analysis, although it has happened with fossil hominins before. Most notably, the initial publications of the OH 7 type specimen of Homo habilis included a few bones amid the hominin hand remains, which were later identified as belonging to a large fossil monkey. Subtle anatomical mismatches, like a vertebra that is slightly wrong, require some detailed analysis to discover.

One thing that helps is greater access: As more and more specialists come to study fossil hominins, they bring a breadth of experience with different species and anatomical elements that no single expert can match.

Link: Selection for tall Dutch men

Carl Zimmer comments on a new paper that shows that the exceptionally tall average stature of today’s Netherlands population has been augmented by natural selection during the last fifty years: “Natural Selection May Help Account for Dutch Height Advantage”.

Among those born in the early 1950s, for example, men who were 5 feet 6 inches had on average 2.15 children. Men who were 6 feet 1 inch had 2.39 children. The scientists found that the trend toward taller men having more children persisted for more than 35 years.
Among women, the pattern was more complex. Over all, Dutch women of average height had the most children. But that was because taller women tended to take longer to become mothers. Once they entered their childbearing years, taller mothers had children at a faster rate than shorter women.

Zimmer makes a brief reference at the end of the article to a population in Massachusetts where the evidence goes in the opposite direction. This is the long-term Framingham Heart Study, in which shorter women have consistently shown larger family sizes than taller women. It does seem remarkable that different industrialized nations actually have experienced selection in opposite directions during the last fifty years.

The levels of selection are not small: the difference in lifetime fitness between tall and short Dutch men is more than 10 percent. The change per generation will be lower, because (1) women do not show the same fitness difference, (2) the heritability of stature is around 0.8 or so, and (3) it depends on the distribution of fitness across the population, not just the difference between tall and short classes. But still, 2 or 3 percent of stature per generation is strong selection. Over many generations, that kind of difference would result in a large and rapid change. Of course, without knowing the cause of selection—social dynamics? sexual selection? correlation with some other selected trait?—we can’t predict whether the selection will be maintained in the future.


Notable paper: Saladié P, Cáceres I, Huguet R, Rodríguez-Hidalgo A, Santander B, et al. (2015) Experimental Butchering of a Chimpanzee Carcass for Archaeological Purposes. PLoS ONE 10(3): e0121208. doi:10.1371/journal.pone.0121208

Synopsis: Palmira Saladié and colleagues butchered a dead chimpanzee to study the traces of cutmarks and marrow removal that might characterize cannibalism on Paleolithic human remains. They found that the resulting bone traces were similar to those found in the hominin remains from Gran Dolina, Spain—an early Middle Pleistocene site at which cannibalism has been suggested. And only a minority of the bone fragments from the butchered chimp bore the distinctive traces of human modification.

Interesting because: They butchered a chimpanzee carcass with stone tools!

But… As far as experimental archaeology goes, a single specimen is not really a sufficient sample for comparison with ancient remains. But it is a rare opportunity to treat the remains of a hominoid in this way, and I’m glad they described the results. Maybe further work with human cadavers will become possible to replicate these patterns with larger samples.


Notable paper: Kay, G. L. et al. (2015) Eighteenth-century genomes show that mixed infections were common at time of peak tuberculosis in Europe. Nat. Commun. 6:6717 doi:10.1038/ncomms7717.

Synopsis: Gemma Kay and colleagues used a metagenomic approach to investigate the tuberculosis infections of eight natural mummified bodies from seventeenth-century Hungary. They found that five of the individuals carried multiple strains of tuberculosis, and that all the strains in these bodies are of types still present in Europe today.

Interesting because: Our understanding of the past epidemiology of tuberculosis has rapidly grown, mostly due to ancient DNA techniques. Last year, research on ancient remains from Peru showed that ancient people may have obtained tuberculosis from seals, only to be replaced by Old World human tuberculosis lineages in post-Columbian times. Research on historic remains from Europe, Asia and Africa will help to understand the dynamics of tuberculosis in those populations.


My UW-Madison mathematics colleague Jordan Ellenberg has an interesting feature in Nautilus that describes a simple model capable of generating very complex behavior: “The Amazing, Autotuning Sandpile”. The dynamics of sand tumbling down when it reaches a critical point may help to inform us about the dynamics of social forces in the real world.

Real-world political phase transitions tend to happen not in neat sequences, but in sudden coordinated fits, like the Arab Spring, or the collapse of the Eastern Bloc. These reflect quiet periods punctuated by crises—like a sandpile. You can add grains of sand to the top of a sandpile for a while, to no apparent effect. Then, all at once, an avalanche sweeps sand down from the top in an irregular pattern, possibly setting off little sub-avalanches as it goes.
This analogy doesn’t necessarily get us anywhere. After all, real sand is hard to analyze, just like real politics. But here’s the miracle. A kind of abstraction of a sandheap, known as the “abelian sandpile model,” created by physicists Per Bak, Chao Tang, and Kurt Wiesenfeld in 1987, seems to capture some of the rich, chaotic features of real sandpiles, not to mention other complex systems from biology, physics, and social science—while remaining simple enough to study mathematically.

I think about sandpile models quite a lot. While Ellenberg focuses in this article upon the intricate fractal patterns that simple rules can generate, I find other issues more relevant, including the interaction of randomness with critical thresholds.


Notable paper: Heyer, E., Brandenburg, J.-T., Leonardi, M., Toupance, B., Balaresque, P., Hegay, T., Aldashev, A. and Austerlitz, F. (2015), Patrilineal populations show more male transmission of reproductive success than cognatic populations in Central Asia, which reduces their genetic diversity. American Journal of Physical Anthropology. doi:10.1002/ajpa.22739

Synopsis: Heyer and colleagues examined Y chromosome and mtDNA from several populations in Central Asia, including patrilineal populations (where inheritance is determined by the father’s line) and cognatic populations (where inheritance is determined by both parents’ lines). They found that gene genealogies indicate a substantial inheritance of reproductive success in most of the societies they examined, and in the patrilineal populations that inheritance of reproductive success especially determined a low variation of the Y chromosome relative to mtDNA and the autosomes.

Interesting because: Human populations are relatively inbred. One way that inbreeding can happen in a large population is if fitness is inherited: that is, most people tend to come from a few large families, and these tend to propagate through time. That’s exactly what Heyer and colleagues document in many of these Central Asian populations.

Sheds light upon… Recently, another study reported that Y chromosome diversity shows a bottleneck in early farmers. The press around that study concentrated upon a literal bottleneck, with a reduction in the number of males. In reality, an inheritance of reproductive success by males can explain the proliferation of a few patrilines in ancient people. That is, some measures of genetic variation can decrease even as population size is rapidly increasing, as long as some patrilines are increasing disproportionately.

Writing Anthropocene with a small 'a'

This week in Science, a short commentary by William Ruddiman and colleagues challenges the idea that scientists should recognize an Anthropocene epoch as having begun in the postwar era. They argue that this date does not recognize the massive human alterations to biomes that began well before the development of agriculture and accelerated during the Holocene:

Selecting 1945 as the start of the “Anthropocene” would implicitly omit these extensive agricultural and early-industrial alterations. Does it really make sense to define the start of a human-dominated era millennia after most forests in arable regions had been cut for agriculture, most rice paddies had been irrigated, and CO2 and CH4 concentrations had been rising because of agricultural and industrial emissions? And does it make sense to choose a time almost a century after most of Earth's prairie and steppe grasslands had been plowed and planted? Together, forest cutting and grassland conversion are by far the two largest spatial transformations of Earth's surface in human history. From this viewpoint, the “stratigraphically optimal” choice of 1945 as the start of the Anthropocene does not qualify as “environmentally optimal.”

Those who favor defining an “Anthropocene” epoch want us to recognize that industrialization caused global effects, for example, chemical changes to soil composition, changes in the proportions of atmospheric components, introduction of radioisotopes to the biosphere, massive replacement of tropical forest by monocultures, construction of massive dams, and a great acceleration in the rate of extinction of species worldwide. But many of these processes began much earlier in time, at or before the dawn of agriculture. Moreover, many of the processes important in the early industrial era actually began to reverse after 1945. For example, many long-dammed rivers have been freed during the last seven decades, while a vast area of North America once cleared for farming has now become secondary forest. And even the postwar era has not been static: Radioisotopes spiked during the heyday of atmospheric atomic testing, but have markedly declined since then.

Ruddiman and colleagues extend this argument and point to a deep problem with the Anthropocene concept: It cannot be distinguished from the Holocene. The processes that humans have deployed within the last seventy years have, at some scale, defined all of human history.

The Anthropocene concept is mostly about politics, and not at all about geology. It does raise an important question for academic geology, and a timely one: To what extent can the major transitions in Earth’s history be described by discrete causes? With the Holocene and Anthropocene, we are talking about differentiating causal effects that have unfolded across a mere 10,000 years. Probably in no other case in Earth’s history can we hope to attain such temporal resolution on the processes that led to faunal turnover and broad-scale biotic change. Even with the Cretaceous-Tertiary boundary, where the hypothesis of an impact-mediated extinction is very well supported, the overall pattern of extinction and biotic turnover may have taken longer than the Holocene.

Ruddiman and colleagues suggest a solution:

Despite differing views, the term “Anthropocene” is clearly here to stay. One way forward would be to use the term informally (with a small “a”). This approach would allow for modifiers appropriate to the specific interval under discussion, such as early agricultural or industrial. In this way, we could avoid the confinement imposed by a single formal designation, yet acknowledge the long and rich history of humanity's environmental transformations of this planet, both for better and for worse.

In other words, allow the Anthropocene concept to shape academic discussion, without letting it into the textbooks as a formal equivalent of Holocene. This lets us recognize the ways that human activity have come to shape the planet, and likewise recognizes that no single inflection point can suitably distinguish human from natural effects.

I haven’t entirely decided what I think about the Anthropocene concept. So far, most of the Anthropocene boosters have seemed to be mostly concerned with public relations, not building new scientific insights. They have largely ignored the capabilities of early farmers, not to mention things like the intentional management of grassland ecosystems with fire by ancient Australians and New World peoples. We have been shaping Earth to our will for many thousands of years, which should be obvious to anybody familiar with archaeology. The geologists proposing the Anthropocene concept have seemed oblivious to this record.

I do like that the Anthropocene concept recognizes that feedback from biotic processes (including human activity) may have caused major transitions in Earth’s history. It would be interesting to examine how much the Holocene resulted from human activity—for example, in contrast to earlier Pleistocene interglacials. I would like to see this aspect of the science grow.

Reference

Ruddiman WF, Ellis EC, Kaplan JO, Fuller DQ. 2015. Defining the epoch we live in. Science 348:38-39. doi:10.1126/science.aaa7297


Notable paper: Pampush, James D. (2015) Selection played a role in the evolution of the human chin. Journal of Human Evolution (in press) doi:10.1016/j.jhevol.2015.02.005

Synopsis: Pampush examined the angle of inclination of the mandibular symphysis in 123 primate species, finding that the apparent rate of evolution of the mandibular symphysis in the human lineage was unusually high (77 times faster than the average across the primate evolutionary tree). This argues that the human chin has evolved under selection rather than random genetic drift.

Interesting because: It’s strange that people all over the world today have a bony bar on the front of their mandibles. Hardly any Middle Pleistocene humans and no other primates have such a trait. Anthropologists have used the chin as a marker of modern humans, arguing that any mandible bearing a chin must be one of our close fossil relatives. They equally argue over the definition of the chin itself. But we really don’t know why the trait became common in Late Pleistocene people. It’s very clever that Pampush uses the primate phylogeny to establish a rate distribution for mandibular symphysis morphology, because instead of examining only the maximum rate of change by genetic drift, this distribution considers humans in comparison to the constraints on evolution in other species.

Wait, isn’t this obvious? Actually, it’s surprisingly difficult to demonstrate that a morphological trait has been under selection in the fossil record. One problem is that genetic drift can cause almost any pattern of evolutionary change, in principle, as long as (a) the population was fairly small, or (b) the change took a long time to happen. Human evolution took millions of years, and the population sizes of our ancestors were a lot smaller than today’s population, so drift was more powerful in the past. Another problem is that we tend to notice the traits that changed a lot, but don’t tend to notice the ones that stayed the same. In other words, our attention is biased and this bias makes us likely to ascribe changes to selection just because they are changes. To test the hypothesis of genetic drift, we need to consider the probability that a given amount of change could happen by chance over the long span of time involved. Clearing that bar is very difficult.

You make it sound like this study doesn’t answer the question. Here’s the thing: With natural selection, there must be some connection between the trait and the organism’s survival or reproduction. How did a chin make people survive more, or reproduce more? Showing that selection must have influenced the evolution of the trait doesn’t show that the trait itself was important—change in the mandible may have been a side-effect of selection on the face, or the skull, or the dentition. We can speculate about whether chinny humans had a reproductive advantage—chins are sexy, bruh—but we lack a good test of the hypothesis.

Is Little Foot really 3.67 million years old?

Darryl Granger and colleagues report in Nature this week on the date of the StW 573 specimen, commonly known as “Little Foot”, from Sterkfontein, South Africa. They estimate the skeleton’s age at 3.67 million years old, an age slightly older than the footprints at Laetoli, Tanzania, which would make the South African skeleton roughly contemporary with the East African species Australopithecus afarensis, and earlier than Kenyanthropus platyops. The skeleton might thus be the oldest known hominin specimen in South Africa, although the fossils from the Jacovec cavern of Sterkfontein may be as old or older, as argued first by Partridge and colleagues (2003).

Does it matter? The age of the skeleton is irrelevant to its relationships, but may give some insight into the ecology of early hominins.

Stw 573 is an impressively complete skeleton of an early hominin, from the Silberberg Grotto deep within the Sterkfontein cave system. The skeleton was completely enclosed in a hard concrete-like breccia when it was first discovered, and the excavation has now taken more than 20 years. Some foot bones of the specimen were the first part to be uncovered, and were described in 1995 by Ron Clarke and Phillip Tobias. Later, other parts of the skeleton were discovered and a paper by Clarke (1998) presented basic details about the discovery. The excavators approached it very cautiously, taking years to extract blocks of breccia from the cave for preparation in the laboratory. As yet, only a handful of anatomical observations have been reported.

Without seeing the specimen, I cannot really say anything about its morphology or relationships. There are photos of the specimen but these all show the remains to be substantially distorted, apparently with some crushing and with plastic deformation of the breccia deposit. The fossil is beautiful, but studying the anatomy of this skeleton is going to be a tough job.

What about the name, Australopithecus prometheus? Raymond Dart gave this name to the first hominin specimen from Makapansgat, MLD 1, a piece of the posterior part of a cranial vault. As you can see from the bone itself, it gives very little information about the anatomy of the skeleton as a whole:

MLD 1, posterior view
Yeah, other people give you bootleg photos of Little Foot. I give you the real Australopithecus prometheus. MLD 1, posterior view. John Hawks CC-BY-NC-ND

Clarke (2008) has argued that the Sterkfontein and Makapansgat samples include two distinct fossil species. In Clarke’s view, Australopithecus africanus, which was identified by Dart at Taung, is a smaller-toothed species with a more elongated cranium, narrow nasal bridge, and posteriorly-placed cheeks. In contrast, Australopithecus prometheus includes those specimens that have anteriorly-placed cheeks, larger, bulbous molars and premolars, large canines and incisors, widely-spaced orbits and a sagittal crest. Clarke uses Au. prometheus for this set because the temporal lines of MLD 1 appear to have converged at the superiormost point on this cranial fragment. They may have formed a slight sagittal crest, although the crest itself is not preserved here. Clarke has argued (2013) that this feature and other aspects of the occipital morphology connect MLD 1 with some Sterkfontein specimens, including the StW 573 skeleton, and that in the StW 573 skull, those features of the posterior vault occur together with the bulbous teeth found in specimens like StW 252. In other words, for Clarke, Little Foot is the keystone that holds Australopithecus prometheus together.

I cannot evaluate that hypothesis without the evidence.

Other paleoanthropologists treat nearly all the South African material from Sterkfontein and Makapansgat as representatives of a single, highly variable species, Au. africanus. We know that these samples extend over a very long period of time, perhaps a million years. The largest number of specimens come from Member 4 of Sterkfontein, which includes an immense deposit of breccia in which it has been hard to establish a clear chronology. Given the extent of time involved, we might guess that a single species assemblage would sample populations that varied substantially from time to time. Clarke claims that the differences between his two proposed species Au. africanus and Au. prometheus are consistent, and that each includes clear male and female examples. I wait to see the evidence.

Coming back to the issue of the date: Granger and colleagues used a method of dating based on the exposure of surface rocks to cosmic rays, which is known as cosmogenic nuclide dating. Oxygen-16 and silicon-28 are among the most common isotopes in the Earth’s crust, and both are components of the crystalline quartz found commonly in sand grains and chert. On the Earth’s surface, atmospheric particles and rocks are occasionally bombarded by high-energy cosmic rays, and these microscopic high-energy collisions create cascades of secondary particles. Some of these smash into quartz, converting oxygen-16 into beryllium-10, and silicon-28 into aluminum-26. Both these isotopes are radioactive and decay at different rates. If the quartz crystalline material is then buried deep underground in a cave breccia, the creation of new aluminum-26 and beryllium-10 stops, and the ratio between the two elements steadily changes as both isotopes decay. The ratio is a natural measure of the length of time since the material was introduced into an underground environment. Granger and colleagues examined this ratio in many rock samples from nearby the StW 573 skeleton, all of them together allowing a more precise estimate of the date that the rock samples were buried than any could individually.

Of course, to accept the date for the skeleton we must assume that it entered the deep chamber at the same time as the rock samples. If the rock samples had been reworked from earlier sediment deposits in the cave, then they might have much older ages than the fossils. In this paper, 9 quartz samples together are consistent with the same age (the 3.67 million year age is estimated as an isochron from this consistency across samples, not independently from the different samples). That makes it seem unlikely that the breccia composition has been systematically reworked from sediment that had lain underground for much longer than the fossils included in the breccia. Still, the geology is complex. Flowstone around the fossil yields a much lower age, around 2.2 million years, but Bruxelles and colleagues (2014) have argued that the flowstone formed much later, after the breccia bearing the skeleton had cracked and settled.

Accepting an early date for StW 573 does not weigh either toward or away from recognizing Au. prometheus as a valid species. The anatomy is the anatomy, whatever its age, and only the anatomy can determine whether StW 573 and possibly other specimens can be distinguished from the variability of Au. africanus. A phylogenetic analysis that includes that anatomy might be very interesting—I could even imagine that a reduced Au. africanus might look much more like Homo than the expanded sample, and StW 573 and a handful of other specimens might be more different from Homo than was Au. afarensis.

From the point of view of ecology, I cannot see any reason why early hominins did not enter southern Africa early in the Pliocene. They were established from Tanzania to Ethiopia by 3.6 million years ago, and the 3.4-million-year-old Bahr-el-Ghazal mandible shows that at least one australopith had spread across the Sahel region during the same time period. They should have reached southern Africa as well.

What happened to them there? An early date for Little Foot might help to establish whether southern hominins had already become different from their eastern counterparts. An early date would help us to evaluate whether climatic or other environmental factors had influenced the early habitation of southern Africa by hominins.

References

Granger DE, Gibbon RJ, Kuman K, Clarke RJ, Bruxelles L , Caffee MW. 2015. New cosmogenic burial ages for Sterkfontein Member 2 Australopithecus and Member 5 Oldowan. Nature doi:0.1038/nature14268

Clarke, R. J., & Tobias, P. V. (1995). Sterkfontein Member 2 foot bones of the oldest South African hominid. Science, 269(5223), 521-524.

Clarke, R. J. (1998). First ever discovery of a well-preserved skull and associated skeleton of Australopithecus. South African Journal of Science, 94, 460-463.

Clarke, R. J. (2008). Latest information on Sterkfontein's Australopithecus skeleton and a new look at Australopithecus. South African Journal of Science, 104(11-12), 443-449.

Clarke, R. (2013). Australopithecus from Sterkfontein Caves, South Africa. In The paleobiology of Australopithecus (pp. 105-123). Springer Netherlands.

Partridge, T. C., Granger, D. E., Caffee, M. W., & Clarke, R. J. (2003). Lower Pliocene hominid remains from Sterkfontein. science, 300(5619), 607-612.doi:10.1126/science.1081651

Bruxelles, L., Clarke, R. J., Maire, R., Ortega, R. & Stratford, D. Stratigraphic analysis of the Sterkfontein StW 573 Australopithecus skeleton and implications for its age. J. Hum. Evol. 70, 36–48 (2014)

How the NSF Graduate Research Fellowship is slowly turning into a dissertation grant

Terry McGlynn is a faculty member at California State University, Dominguez Hills, a teaching-intensive undergraduate institution. In his role mentoring undergraduates in ecology and evolutionary biology, he has helped many to prepare applications to the NSF for the Graduate Research Fellowship Program (GRFP). After the notifications about this year’s fellowships came out this week, McGlynn looked into the numbers, and was surprised at what he found: “NSF Graduate Fellowships are a part of the problem”.

Undergrads from all Cal State campuses had a combined total of 37 awards. Harvard undergrads had 37 awards.
According to Wikipedia, the undergraduate enrollment of the CSU campuses is 392,951. Whereas the undergraduate enrollment at Harvard is 6,700.
Considering that I spend so much of my professional life preparing my undergraduates for career in science, this makes me realize that I’m pushing up against a goddamn unmoveable object. The tremendous success I had this year — with one student getting a GRFP! — would simply be the notch on the belt of PIs who are working at institutions with so much more support at every level.

I want to expand on McGlynn’s analysis, because I think there is another problem with the GRFP: a good fraction of GRFP fellowships today go to students who are already enrolled in graduate programs, not undergraduates. Providing funds for students already doing graduate work can help support talented people “with the potential to be high achieving scientists”. But the current program vastly advantages those students who are already working closely with scientific mentors within large, well-funded graduate programs.

Of course, this helps to explain why Harvard has as many GRFP recipients as the entire Cal State system. More than half the Harvard recipients are already graduate students. Many are working intensively with faculty advisors on graduate-level projects that will become the basis of their dissertations.

Last year, the NSF commissioned a report on the GRFP, which is available online “Evaluation of the National Science Foundation’s Graduate Research Fellowship Program”. In their sample of fellows from previous years, 57.7 percent had received the award while enrolled in a graduate program. I wanted to look more deeply into this statistic, because my perception has been that these fellowships are becoming more and more directed toward graduate students in biological anthropology and archaeology. The information from NSF does not make it easy to see how many of the fellowships within a particular field are awarded to those already attending graduate programs, or among those how many are relatively advanced in their degree progress. The list of awarded fellowships this year is online, and a first guess is that students who are already in graduate programs will have a different “present institution” from their “baccalaureate institution”. I make that assumption only tentatively, since the criteria for listing current institution are not explicit, and a few students may attend graduate school at their undergraduate institution. Also, some students may presently be enrolled in terminal masters programs, or may be looking to change institutions with the portable NSF fellowship award.

A look at the new GRFP recipients in biological anthropology and archaeology shows that only a very small fraction of them (7 out of 27) are still at their baccalaureate institution. An additional four list no present institution, which may mean that they are in a gap year or returning to graduate work after some time in another career. The strong majority of NSF graduate fellowships in biological anthropology and archaeology this year appear to be going to students already enrolled in a graduate program. I haven’t tabulated any other numbers for this year, but that puts these fields far above the average in funding current graduate students above undergraduate seniors. That’s no criticism of these fellowship awardees, all of whom must be excellent students. But it does indicate that in biological anthropology and archaeology, the GRFP mostly funds students who have already begun their graduate course of study.

Giving GRFP fellowships to first- or second-year graduate students in a small set of elite graduate programs is intellectual canalization. Most of these students have already chosen a faculty advisor and those advisors provide extensive guidance on projects and proposals. Some programs treat these fellowship proposals as an opportunity to score “bonus” support for their existing students, freeing university funds to expand their graduate student cohort. There is no question that the fellowships are good for most of their recipients, and support their training as scientists. But the stage of career makes a difference. A fellowship given to a graduating senior at the time she chooses her graduate program enables her to choose the best faculty mentor from across the U.S., with much less regard to institutional funding and guaranteed support for the first three years of training. A fellowship given during the second year of graduate training will tie the recipient more deeply to the mentor who helped her develop the successful proposal, which will thereby support three years of dissertation work. The more we expect applications to look like research proposals, the more the GRFP looks like a mega-version of the Dissertation Improvement Grant (DIG) program.

I think that’s bad for science.

I think that NSF would be wiser to tie their fellowship funding to undergraduate accomplishment. When awarded to seniors, the fellowships can enable independence at the time of graduate program decisions, and they have some chance to actually draw students into STEM from other fields.

I write from some experience. As a college senior, I was still deciding my career path, and I chose biological anthropology at the last minute. I was not an NSF fellow; I had a different fellowship. But it had the same effect: As a student, the availability of funding for science can be a major influence on the decision to enter a scientific field, and can enable the student to choose an institution without regard to funding status at that institution.