Header image

john hawks weblog

paleoanthropology, genetics and evolution

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

High recent admixture reported for Oase 1

Some readers have asked me what I think of the reporting from the recent Biology of Genomes conference, that Qiaomei Fu and colleagues from Svante Pääbo’s group have demonstrated a very recent Neandertal ancestry for the famous mandible from Peștera cu Oase, Romania. This is the earliest-known “modern” human in Europe, around 40,000 years old. For example, this report from Ewen Callaway: “Early European may have had Neanderthal great-great-grandparent”.

They estimate that 5–11% of the bone's genome is Neanderthal, including large chunks of several chromosomes. (The genetic analysis also shows that the individual was a man). By analysing how lengths of DNA inherited from any one ancestor shorten with each generation, the team estimated that the man had a Neanderthal ancestor in the previous 4–6 generations. (The researchers declined to comment on the work because it has not yet been published in a journal).

I have two thoughts:

  1. This is no surprise.
  2. I’m very pleased that the authors are talking about this work at meetings and that journalists are reporting on the work. I hope that the broader awareness of this work as it is happening will cause other people to find things they might not have noticed before. I also hope that it will not prejudice the publication of this work in a high profile journal, should the authors choose to pursue that route.

OK, I have more than two thoughts, but unfortunately, until I see the details I won’t be able to comment intelligently on most of the interesting questions. I do wonder: Why does anyone think they can tell a Neandertal from a “modern human” in this time period from a tooth?

Of course, all the facts are already on Wikipedia…

No Australopithecus boisei from the Afar

I was reading Scott Simpson and colleagues’ article from March 2014, “The female Homo pelvis from Gona: Response to Ruff (2010)”, in which they go through reasons why the BSN49/P27 fossil pelvis belongs to Homo and not, as Ruff has suggested, some version of Australopithecus or Paranthropus.

I blogged about the anatomy of the Gona pelvis (BSN 49/P27) when it was first published in 2008: “Mrs. Elvis, the Homo erectus pelvis”, and raised all the issues that have since become features of the scientific literature. It is a very interesting problem, because BSN49/P27 is only a pelvis; no other skeletal remains have been found from the same individual. Diagnosing pelvic anatomy as belonging to Homo is an interesting problem right now, because of the lack of evidence about pelvic anatomy in late australopiths such as Australopithecus boisei and the presence of Homo-like features in the pelvis of Australopithecus sediba.

I wanted to flag an interesting observation to which I haven’t given much thought before: Au. boisei has not been found at any of the Afar sites. This comes in Simpson and colleagues’ argument that the Gona pelvis BSN49/P27 must be Homo because only Homo has been found in the area during the same time interval.

Finally, Ruff proposed that the Gona pelvis could possibly have been a representative of a species outside of the genus Homo, such as Au. (P.) boisei. Unfortunately, no fossils were allocated to this species in his analysis. No pelvis of Au. (P.) boisei is known and no Australopithecus have been discovered from the Afar region that are younger than 2.5 Ma. Fossils representing the ‘robust’ group were all from Swartkrans and assignable to Au. (P.) robustus. While assigning the Gona pelvis to Au. (P.) boisei might seem like a possibility, the absence of any known comparative material makes this assignment untestable as it is not based on comparative data.

Later in the paper, they reiterate this point:

Despite significant effort surveying for fossils, no specimens attributable to Au. (P.) boisei are known from the Afar region. The Konso, Ethiopia ( Suwa et al., 1997) specimens are the northernmost representatives currently known. Currently, Au. (P.) boisei is not known from any deposits younger than 1.4 Ma ( Suwa et al., 1997). Thus, the 0.9–1.4 Ma Gona pelvis, if it was assignable to Au. (P.) boisei, would be the unique representative from the Afar region and the last appearance datum for this species.

This is perhaps less surprising than it sounds at first, because there are no other Homo specimens reported from Afar during the time span between the date reported for the A.L. 666-1 specimen (2.33 million years) (Kimbel et al. 1997) and the much later Daka specimens (Asfaw et al. 2002) around a million years old. Based on the stratigraphic information published by Simpson et al. (2008), the Gona pelvis lies either within this gap or at the tail end of it.

Amid such a near-total lack of fossil evidence, I wouldn’t readily dismiss the idea that some late australopith may have been present in the Afar area during the Early Pleistocene.

But what would it mean if Au. boisei and other late australopiths really never lived in the Afar area? An absence from Afar would contrast strongly with the Turkana Basin, where Au. boisei is the most common fossil hominin within the sediments leading up to 1.4 million years ago. The Turkana Basin includes a good fraction of southern Ethiopia, where what may be the earliest occurrence of Au. boisei is in the Shungura Formation. The latest occurrence of Au. boisei is also in southern Ethiopia, near Konso. Some recent species do have biogeographic distributions that suggest a split between northeastern and southern Ethiopia; whether such a split was present or relevant for Au. boisei may be worth investigation.

It is a bit odd that no robust australpiths are yet known from North Africa or West Asia. Theropithecus—the genus including living geladas—existed as far as Morocco and India during the Pleistocene. The usual reconstruction of australopiths would suggest they should have been able to disperse effectively through savanna and along rivers and coastlines. Maybe Au. boisei will yet be found outside of its known Rift Valley range.

References

Asfaw, B., Gilbert, W. H., Beyene, Y., Hart, W. K., Renne, P. R., WoldeGabriel, G., ... & White, T. D. (2002). Remains of Homo erectus from Bouri, Middle Awash, Ethiopia. Nature, 416(6878), 317-320. doi:10.1038/416317a

Kimbel, W. H., Johanson, D. C., & Rak, Y. (1997). Systematic assessment of a maxilla of Homo from Hadar, Ethiopia. American Journal of Physical Anthropology, 103(2), 235-262. doi:10.1002/(SICI)1096-8644(199706)103:2<235::AID-AJPA8>3.0.CO;2-S

Ruff, C. (2010). Body size and body shape in early hominins–implications of the Gona Pelvis. Journal of Human Evolution, 58(2), 166-178. doi:10.1016/j.jhevol.2009.10.003

Simpson, S. W., Quade, J., Levin, N. E., Butler, R., Dupont-Nivet, G., Everett, M., & Semaw, S. (2008). A female Homo erectus pelvis from Gona, Ethiopia. Science, 322(5904), 1089-1092. doi:10.1126/science.1163592

Simpson, S. W., Quade, J., Levin, N. E., & Semaw, S. (2014). The female Homo pelvis from Gona: response to Ruff (2010). Journal of human evolution, 68, 32-35. doi:10.1016/j.jhevol.2013.12.004


Chanda Prescod-Weinstein has written an evocative essay about her experience becoming a physicist, and the daily frustrations and challenges of being different in background from those ordinarily welcomed into the field: “Let Physics Be the Dream It Used To Be”

I’m not going to catalog every shitty thing that happened to me in grad school or as a postdoc even though I haven’t actually mentioned the worst stuff, but the point is that I didn’t and still don’t fit into the dominant astro/physics culture, and this has really sucked a lot of the fun out of physics for me. White astro/physicists need to understand and take to heart that this is in fact a real issue that doesn’t magically go away with admissions and diversity initiatives that fail to address underlying cultural, structural issues.

She reminds us that science as a career choice has many unappealing qualities, particularly for those who lie outside a particular social background.


Many people know the story that Carl Sagan was rejected for membership in the National Academy of Sciences of the United States. The story has given rise to the idea of the “Sagan Effect”, whereby scientists who are active in popularizing and explaining science to the public are perceived by other scientists as being somehow less serious about their research.

Someone asked me about this today and I ran across a quote from the journalist Joel Achenbach, who had profiled Sagan in 1996, in an article reprinted in the book, Conversations with Carl Sagan (Carl Sagan and Tom Head, editors, 2006). This excerpt is from page 158:

In 1992, Sagan's name was one of sixty nominated for membership in the National Academy of Sciences. The other fifty nine made it without a hitch. But someone objected to Sagan.
Sagan's case was argued by Stanley Miller, a chemist who did pioneering work on the origin of life. He believes Sagan's scientific work, such as his research on the atmosphere of Venus, is often overlooked. The anti-Sagan faction countered that if the fluffy stuff of Sagan's career were swept away, there wouldn't be enough hard science underneath.
One member who was present says, "If he had not done television, he probably would be in the academy."

Theodosius Dobzhansky, “Man and Natural Selection” (American Scientist 49:285, 1961):

By changing what man knows about the world, he changes the world he knows; and by changing the world in which he lives, he changes himself. Herein lies a danger and a hope; a danger because random changes of the biological nature are likely to produce deterioration rather than improvement; a hope because changes resulting from knowledge can also be directed by knowledge.

Ars Technica has a long article in honor of the anniversary of the Apollo 13 by writer Lee Hutchinson, giving background to the famous accident that the movie (and books that I’ve read about the space program) omitted: “45 years after Apollo 13: Ars looks at what went wrong and why. I’ve never read such a clear account of why the oxygen tank exploded.

And the real moral of the story:

For Apollo 13, keeping calm and working the problems as they appeared allowed three astronauts to escape unharmed from a complex failure. The NASA mindset of simulate, simulate, simulate meant that when things did go wrong, even something of the magnitude of the Apollo 13 explosion, there was always some kind of contingency plan worked out in advance. Controllers had a good gut-level feel for the limits of the spacecraft’s systems when trying to work through emergency problems.

Esther Ingliss-Arkell has an interesting short description of “What Happens When You Get The Wrong Blood Type?” on io9.

The first sign of a transfusion gone wrong is "a feeling of impending doom." This is a legitimate medical symptom, and doctors who regularly work with blood transfusions are told to look for it. Other sign of a mismatched blood type is the usual immune system warning flags — flu-like fever, ache, and chill, as well as a burning sensation at the injection site.

I teach the ABO system as part of my usual human genetics lectures, and I’ve never read a great description of the range of transfusion reactions—I was really only aware of the most catastrophic type. So this can be an interesting piece for those teaching ABO as well as those who’ve just always wondered.

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.