The 85th annual meeting of the American Association of Physical Anthropologists, in Hottlanta this year, is only a few short weeks away. The preliminary program is up, and there’s really a lot to look forward to at this year’s conference. There’s a session dedicated to Homo naledi on Saturday morning (16 April), and I’ll be presenting on dental development in Homo naledi at the very end of the last session of the day. Leading up to the conference, I’ll be tweeting teasers as I put together my talk.
My colleague David Pappano and I are also organizing a workshop on using R in biological anthropology, which will take place on Friday 15 April from 9:30-11:30 am. The goal of the workshop isn’t to make you an expert in R by the end of the two short hours, but rather to introduce you to the basic functions and potential uses of the powerful, free statistical software. So if you’Re Ready to leaRn some R basics, come to Room A601 on FRiday moRning – it’s fRee and no RegistRation is RequiRed.
Hopefully we’ll see you in Atlanta in a few weeks!
Ancient DNA studies keep on delivering awesome findings about human evolution. Continuing this trend, Matthias Meyer and colleagues report today in Nature nuclear DNA (nDNA) sequenced from ~430,000 year old humans from the Sima de los Huesos (SH) site in Spain. SH is badass not only because the name translates as “pit of bones,” but also because the pit has yielded hordes of fossils comprising at least 28 people (Bermudez de Castro et al., 2004), and some of these bones preserve the oldest human DNA yet recovered (Meyer et al., 2013).
Point 1 in Northern Spain, is Sima de los Huesos. The rest of the points are other sites where hominin fossils preserve ancient DNA. Figure 1. From Meyer et al. 2013.
Anatomically, the SH hominins have been interpreted as “pre-Neandertals,” having many, but not all, of the characteristics of geologically younger fossils we know as Neandertals. Mitochondrial DNA (mtDNA) obtained from one of the SH femurs was found, surprisingly,to be more similar to Densivan than to Neandertal mtDNA (Meyer et al., 2013), not what would be expected if the SH hominins were early members of the Neandertal lineage. Meyer et al. interpreted this to mean that perhaps the SH hominins were ancestral to both Neandertals and Denisovans, though they noted that nDNA would be necessary to uncover the true relationships between these fossil groups.
Writing about the SH mtDNA in 2013, I noted that mtDNA has failed to reflect hominin relationships before. The distinctiveness of Denisovan mtDNA initially led to the idea that they branched off before the Neandertal-modern human population divergence (Kraus et al. 2010), and therefore that humans and Neandertals formed a clade. Later, nDNA proved Denisovans and Neandertals to be more closely related to one another than to humans (Reich et al., 2010). Then I’m all like, “Hopefully we’ll be able to get human nuclear DNA from Sima de los Huesos. When we do, I predict we’ll see the same kind of twist as with the Denisova DNA, with SH being more similar to Neandertals.”
I made that prediction right before telling Josh Baskin he’d be big.
And lo, Meyer et al. (2016) managed to wring a little bit more DNA out of this sample, and what do they find: “nuclear DNA sequences from two specimens … show that the Sima de los Huesos hominins were related to Neandertals rather than Denisovans” (from the paper abstract).
This is not a surprising outcome. The SH hominins look like Neandertals, and mtDNA acts a single genetic locus – the gene tree is unlikely to reflect the species tree. What’s more, this is similar to the story mtDNA told about human and Neandertal admixture. The lack of Neandertal mtDNA in any living (or fossil) humans was taken to reflect a lack of admixture between early humans and derelict Neandertals, but more recent nDNA analysis have clearly shown that our ancestors couldn’t help but become overcome with lust at the sight of Neandertals (and Denisovans) in Eurasia.
So here ancient DNA corroborates the anatomy that suggested the SH hominins were early members of the Neandertal lineage. This new study also raises the question as to what’s going on with mtDNA lineages – Meyer et al. suggest that the SH mtDNA was characteristic of early Neandertals, later to be replaced by the mtDNA lineage possessed by known Neandertals. They suggest an African origin for this new mtDNA, though I don’t see what that has to be the case. It also raises the question whether the difference in early (SH) vs. later Neandertal mtDNA reflects local population turnover/replacement, or a selective sweep of an adaptive mtDNA variant. Either way, Meyer et al. have done a remarkable job of making astounding discoveries from highly degraded, very short bits of super old DNA. I can’t wait to see what ancient DNA surprises are yet to come.
References Bermudez de Castro, JM., Martinón-Torres, M., Lozano, M., Sarmiento, S., & Muela, A. (2004). Paleodemography of the Atapuerca: Sima De Los Huesos Hominin Sample: A Revision and New Approaches to the Paleodemography of the European Middle Pleistocene Population Journal of Anthropological Research, 60 (1), 5-26 DOI: 10.1086/jar.60.1.3631006
Krause, J., Fu, Q., Good, J., Viola, B., Shunkov, M., Derevianko, A., & Pääbo, S. (2010). The complete mitochondrial DNA genome of an unknown hominin from southern Siberia Nature, 464 (7290), 894-897 DOI: 10.1038/nature08976
Meyer, M., Fu, Q., Aximu-Petri, A., Glocke, I., Nickel, B., Arsuaga, J., Martínez, I., Gracia, A., de Castro, J., Carbonell, E., & Pääbo, S. (2013). A mitochondrial genome sequence of a hominin from Sima de los Huesos Nature, 505 (7483), 403-406 DOI: 10.1038/nature12788
Meyer, M., Arsuaga, J., de Filippo, C., Nagel, S., Aximu-Petri, A., Nickel, B., Martínez, I., Gracia, A., de Castro, J., Carbonell, E., Viola, B., Kelso, J., Prüfer, K., & Pääbo, S. (2016). Nuclear DNA sequences from the Middle Pleistocene Sima de los Huesos hominins Nature DOI: 10.1038/nature17405
Reich, D., Green, R., Kircher, M., Krause, J., Patterson, N., Durand, E., Viola, B., Briggs, A., Stenzel, U., Johnson, P., Maricic, T., Good, J., Marques-Bonet, T., Alkan, C., Fu, Q., Mallick, S., Li, H., Meyer, M., Eichler, E., Stoneking, M., Richards, M., Talamo, S., Shunkov, M., Derevianko, A., Hublin, J., Kelso, J., Slatkin, M., & Pääbo, S. (2010). Genetic history of an archaic hominin group from Denisova Cave in Siberia Nature, 468 (7327), 1053-1060 DOI: 10.1038/nature09710
Usually I use my PowerPoint skills only for evil, like putting together lectures and talks. But sometimes I get distracted. Today, for instance, instead of grading and prepping next week’s lectures on Eugenics and Spine Evo-devo (don’t worry, they’re for different classes), I spent half an hour making this:
A spirited twist on Jane Austen’s classic novel. Why am I devoting my life to research and teaching when I could go to where the real money is?
This is surely the project that will land me tenure in a few years.
After these drawings, my students are now fully trained and ready to tackle the odontological world.
. . . I’ve got dentition on the brain. WHICH IS NOT THEIR ANATOMICAL POSITION.
So last weekend some friends and I hit a local pub, a life jacket for my dental inundation. Surely, a pint and a snack will expunge enamel, dissolve dentine, exhume zuby from my brain! We ordered some beer and baursaki, delicious fried bread made out here in Kazakhstan, the perfect snack to go with beer and chechil. Tearing into the pastry, I started to feel at peace, but then was horrified to look down and find myself hoist with my own petard:
Baursak with a bite taken out? Our a hominin canine?
Seeing the snack, I saw the very thing I’d been fleeing – a hominin canine tooth. Inadvertently, I’d almost exactly replicated Sts 50, a lower left canine crown and broken root from the South African site of Sterkfontein.
Left: Sts 50, lower left canine. Right: bitten fried bread. Images not to scale. ANTIMERES?
They’re nearly identical but from opposite sides (the fancy word for which is “antimeres”). Note the tall-shouldered, sharp apex of the crown, and the little distal tubercle, the little ‘bump’ at the far left in the left picture above. The mesial, or front, crown shoulder is notably taller than the distal tubercle. At probably around 3 million years ago, Sts 50 likely belongs to Australopithecus africanus, and retains an ape-like asymmetrical crown shape compared to the more incisor-shaped canines we humans have today.
Hominin canines and definitely no cakes. Left to right: Homo baursaki, three canines from early Pleistocene South Africa, and a modern human (from White et al. 2011). Images not to scale. Note how much less asymmetrical the modern human canine crown (far right) is compared to the fossil hominins. Teeth 1, 2, 4, and 5 are from the right side while the center, Sts 50, is from the left.
Apparently all you need to go back in time is some beer and baursaki.
We’ve just done the first lab activity in my Human Evo Devo course. My current university is young, and so we haven’t yet acquired good skeletal materials for teaching. Fortunately, the good people at Kyoto University’s Primate Research Institute have made a large, open access database of primate CT scans. For this first lab, students compare skeletons of neonate and adult chimpanzees, getting a crash-course in osteology, CT data, growth-related changes, and chimps.
Neonatal chimpanzee. Three windows give 2D slices in anatomical planes, while the 4th window contains the reconstructed 3D volume that can be rotated and analyzed.
The activity requires a computer lab with the freeware CT analysis program InVesalius. CT files (dicom stacks) can be downloaded from the KUPRI database, but they are massive (100s of MBs), so I recommend some preprocessing before starting the class. I downloaded the specimens we were to use, opened each one in InVesalius, and saved as an .inv3 file. These are on the order of 50-80 Mb each. With smaller, prepared files, it’s faster and easier for students to download and start using them. While the neonate skeleton was small enough to fit into a single dicom stack, the adult scans were so large that I had to use separate files for the the skull, scapula, pelvis, and limbs (pre-separated on the KUPRI database).
Students examined one neonate and adult, making qualitative observations and taking a few cranial and postcranial measurements on each individual.
It’s pretty easy to take linear and angular measurements on both the 3D volume and the 2D slices in InVesalius.
One goal of the assignment is to show students how bones change with growth, in terms of both gross anatomy and overall size. By measuring the diaphyseal lengths, they see what limb bones look like with and without epiphyses.
Measuring diaphyseal, rather than maximum, lengths. Left figure from Jungers and Susman (1984).
Students examine how much size change occurs between birth and adulthood in chimpanzees. They then compare these skeletal sizes and proportional changes with comparable human data (well, up to age 12), taken from Scheuer and Black (2000). This will help get them started thinking about how postnatal growth might lead to differences between adults of each species, or how developmental modifications effect evolutionary changes.
Scheuer L and Black L. 2000. Developmental Juvenile Osteology. Academic Press.
Jungers WL and Susman RL. (1984). Body size and skeletal allometry in African Apes. The Pygmy Chimpanzee: Evolutionary Biology and Behavior, 131-177 DOI: 10.1007/978-1-4757-0082-4_7
Try as I might, I can never escape osteology. Never. Just the other day, I was walking through my school’s expansive, boneless atrium, when these haphazardly scattered letters stopped me in my tracks:
DЯSTUDENSN
Amidst this alphabet soup, there it was, calling out to me. Whispering. Longing….
Ah, the dens. What is the “dens” you ask? It is a special little projection on a special little bone, the second cervical vertebra (C2). Why is it special? Well, most vertebrae look pretty similar to one another, with a body in the front being held in awkward embrace by a bony neural arch in the back.
But not the first two vertebrae, C1 and C2. No, these rebels are spinal celebrities. C1, whose rock name is “Atlas” (presumably in honor of its favorite episode of Wishbone) cradles the skull’s occipital condyles on its concave shoulders. Lacking a true body or centrum, Atlas viewed from the top resembles the gaping maw of a manta ray:
Top: Manta ray. Bottom: Atlas viewed from top, anterior is on the bottom (from Scheuer and Black, 2000). A and F refer to the age at which the bony portions appear and fuse, respectively.
Atlas is a jerk and so it sits right on top of C2, whose rock name is Axis (after the second album by the Jimi Hendrix Experience). More gawky and angsty than Atlas, Axis differs from the rest of the vertebrae in having an extension, the dens, which reaches skyward to boop the inside of Atlas’ maw:
Top: Axis viewed from the front. Bottom: Axis getting pwnd by Atlas. Modified from White et al. (2012).
The most distinctive feature of Axis, aside from its smoldering adolescent rage, is the dens (or odontoid process). If you find a bone fragment that is verily vertebral and has a perpendicular projection, you can bet good tenge you’ve got an Axis. Even a densless fragment can be distinguished from all other vertebrae by its superior articular facets, which are rather flat and face mostly superiorly.
What I thought would be a casual jaunt after class last week turned out to be a horrific reminder of the most amazing vertebrae. This must be how Scott Williams always feels.
This term I’m teaching two of my favorite classes, and I’ve updated their syllabi on my Teaching page. First is a 200-level class about human biological variation and issues surrounding race. Second is my baby, a 300-level on human evolutionary developmental biology. If you want to teach these kinds of classes but don’t want to reinvent the wheel, feel free to use these syllabi to develop your own!
Here are the course descriptions:
Ant 263: Humans and Race
This course examines the nature of human biological variation, in the contexts of genetics, anatomy, history, and society. Students will learn about why humans vary, what this variation does and does not tell us about people, and the ways in which social inequality becomes manifest in human biology. The course will begin by surveying biological variation, both adaptive and selectively neutral, in humans. We will then focus on what the term ‘race’ means biologically, and why this concept does not describe human variation. Moving from biology and genetics, we examine psychological and historical origins of racialist thinking in the United States. This historical overview segues into an analysis of how racial categories are used in biomedical research today. Through the framework of the developmental origins of health and disease, we review the biological mechanisms whereby social inequality results in health disparity.
Ant 364: Human Evolutionary Developmental Biology
What literally makes us human? This class will examine how growth and development were modified over the course of human evolution, to create the animals that we are today. Human anatomy is placed in an evolutionary context by comparison with living primates and the human fossil record. The first half of the course focuses on theory, namely evolution, genetics and life history. The second half examines evidence for the development and evolution of specific parts of the body, from head to toe.
These headlines, each saying something slightly different, are referring to a study by Indjeian and colleagues published in Cell. Researchers identified a stretch of DNA that is highly conserved across mammals, or in other words, it is very similar between very different organisms. In humans, however, this conserved region is actually missing (“hCONDEL.306”):
Fig. 4A from Indjeian et al. 2016. A stretch of DNA on Chromosome 8, “hCONDEL.306,” is very similar between chimpanzees, macaque monkeys, and mice, but is completely missing in humans (as is another stretch, hCONDEL.305).
That a stretch of DNA should be highly conserved across diverse animal groups suggests purifying natural selection has prevented any mutations from occurring here – alterations to this stretch of DNA negatively affected fitness. But that humans should be missing such a highly conserved region suggests that this deletion came under positive natural selection at some point in human evolution. This strategy, of seeking stretches of DNA that are similar between many animals but very different in humans, has led to the identification of hundreds of genetic underpinnings of human uniqueness. Some of these, such as the case in question, involve deleted sequences and have been termed “hCONDELs,” for “regions with high sequence conservation that are surprisingly deleted in humans” (McLean et al., 2011: 216). Others involve the accumulation of mutations where other animals show few or none (e.g., HACNS1; Prabhakar et al. 2008). In many (most?) cases these are “non-coding” sequences of DNA.
How can “non-coding” DNA help make humans upright?
As was predicted 30 years ago (King and Wilson, 1975), what makes humans different from other animals isn’t so much in the protein-coding DNA (the classical understanding of the term, “genes”), but rather in the control of these protein-coding genes. “Non-coding” means that a stretch of DNA may get transcribed into RNA but is not then translated into proteins. But even though these sequences themselves don’t become anything tangible, many are nevertheless critical in regulating gene expression – when, where and how much a gene gets used. It’s wild stuff. Indeed, “Many human accelerated regions are developmental [gene] enhancers” (Capra et al., 2013).
In the present case, hCONDEL.306 refers to the human-specific deletion of a developmental enhancer located near the GDF6 gene, which is a bone morphogenetic protein. The major finding of the paper, as stated succinctly in the Highlights title page, is that “Humans have lost a conserved regulatory element [hCONDEL.306] controlling GDF6 expression…. Mouse phenotypes suggest that [this] deletion is related to digit shortening in human feet.”
How do they link this “gene tweak” to digit shortening?
Since humans have lost this gene enhancer that is highly conserved in other mammals, Indjeian and team reasoned that the chimpanzee DNA sequence associated with this deletion, retaining the enhancer sequence, is likely the ancestral condition from which the human version evolved. They inserted the chimpanzee version into mouse embryos and watched what happened as they developed. The enhancer was only active in the mice’s back legs, specifically in the cartilage that would later become the lateral toe bones and cells that would become a muscle of the big toe (abductor hallucis). These are areas where humans and chimpanzees differ: our lateral toes are shorter than chimps’, and we only have one abductor hallucis muscle whereas chimpanzees have an additional, longer abductor hallucis (Aiello and Dean, 2002). So, we’re on our way to seeing how hCONDEL.306 might relate to our big toe or upright walking, as the headlines say.
But this still doesn’t explain how this deletion affects GDF6 gene expression, and therefore what this does for our feet. Pressing onward, the scientists compared the size of certain bones in mice with a normal Gdf6 gene, and those in which the Gdf6 gene was completely turned off (or “knocked out”). The Gdf6 knock-out mice had shorter lateral toe bones than regular mice, but they also had shorter big toes as well – the previous experiment staining mouse embryos showed the ancestral enhancer was expressed more in the latter toes, not so much the big toe.
Figures 5-6 from Indjeian et al. (2016) sum up the findings. Figure 5 (left) shows that the ancestral version of the GDF6 enhancer (blue staining) is most strongly expressed in the lower half of the body, especially the fifth toe bone. Figure 6 (right) shows that a lack of Gdf6 expression (black bars) results in shorter skull and toe bones. Combining these findings, humans lack a gene enhancer associated with the development of long lateral toes.
hCONDEL.306 doesn’t completely turn off GDF6, so this second experiment doesn’t really tell us exactly what the hCONDEL does. But the results are highly suggestive. Indjeian and team showed that Gdf6 affects toe length, among other skeletal traits, in mice. The ancestral enhancer that humans are missing seems to affect GDF6 activity in the leg/foot only. This illustrates a mechanism of modularity – as the authors state, “Loss of this enhancer would thus preserve normal GDF6 functions in the skull and forelimbs, while confining any … changes to the posterior digits of the hindlimb.” In other words, developmental enhancers allow different parts of the body to evolve independently despite being made by some of the same genes (such as GDF6).
As with any good study, results are intriguing but they raise more questions for future studies. The researchers conducted two experiments to investigate the function of hCONDEL.306: first putting the chimp version in mouse embryos to see where the ancestral enhancer is expressed, and then turning off Gdf6 completely in mice to see what happens. A more direct way to see what hCONDEL.306 does might be to put a longer stretch of the human sequence surrounding GDF6 containing (or rather missing) the ancestral enhancer into mouse embryos. I’m not a molecular biologist so maybe this isn’t possible. But this is important because the ancestral (chimpanzee) enhancer appeared to be most strongly expressed in the little toe, but of course this isn’t our only toe that is short compared to chimps. Similarly, how hCONDEL.306 relates to the abductor hallucis muscle remains in question – does it reduce the size of the intrinsic muscle present in both humans and chimps, or does it prevent development of the longer muscle that chimps have but we lack? We can expect to find hCONDEL.306 in the genomes of Neandertals (and Denisovans?), since they also have short toes, but what would it mean if they retained the ancestral enhancer?
So how does this gene tweak help with upright walking?
This is a really cool paper with important implications for human evolution, but something seems to have been lost in translation between the paper and the headlines (the news pieces themselves are good, though). The upshot of the study is that humans lack a stretch of non-coding DNA, which in chimpanzees (or chimp-ified mice) promotes embryonic development of the lateral toes and a big toe muscle. This may be a genetic basis for at least some aspects of our unique feet that have evolved under natural selection for walking on two legs.
But the headlines misrepresent this result, with words like “led to,” “allowed,” and “caused,” especially when these are followed by “big toe” or “upright walking.” hCONDEL.306 doesn’t really have anything to the big toe bone itself, although it might relate to a muscle affecting our big toe. The only sense in which the “Gene tweak led to humans’ big toe” (first title above) is that hCONDEL.306 might be responsible for our short lateral toes, which make our first toe look big by comparison. The other headlines are misleading since we know from fossil evidence that hominins walked upright long before we have evidence for short toes:
These little piggies get none. Fourth toe bones of living apes and humans (left) and (probable) hominins from 3-5 million years ago (right). I did my best to get all images to scale.
“Epigenetic,” from the fourth article headline, is simply wrong. Modern day epigenetics is a field concerned with the chemical alterations to the structure of DNA. Even the broad concept of epigenetic as originally devised by Conrad Waddington was about how environments (cellular or outside the body) influence development.
It’s hard to fit all the important and interesting information from scientific papers into news headlines. Still, it would be good if headlines more accurately portrayed scientific findings, especially avoiding such definitive verbs as “caused.” Especially in the realm of biology, people should know that there’s a lot that we still don’t know, that there’s lots more important work left to be done.
References
Aiello and Dean, 2002. Human Evolutionary Anatomy. Academic Press.
Capra et al., 2013. Many human accelerated regions are developmental enhancers. Philosophical Transactions of the Royal Society B 368: 20130025.
Indjeian et al. 2016. Evolving new skeletal traits by cis-regulatory changes in bone morphogenetic proteins. Cell http://dx.doi.org/10.1016/j.cell.2015.12.007
King and Wilson, 1975. Evolution at two levels in humans and chimpanzees. Science 188: 107-116 DOI: 10.1126/science.1090005
McLean et al., 2011. Human-specific loss of regulatory DNA and the evolution of human-specific traits. Nature 471: 216-219.
Prabhakar et al., 2008. Human-specific gain of function in a developmental enhancer. Science 321: 1346-1350.
Holy crap 2015 was a big year for fossils. And how fortuitous that 2016 begins on a Fossil Friday – let’s recap some of last year’s major discoveries.
Homo naledi
Some Homo naledi mandibles in order from least to most worn teeth.
The Homo naledi sample is a paleoanthropologist’s dream – a new member of the genus Homo with a unique combination of traits, countless remains belonging to at leasta dozen individuals from infant to old adult, representation of pretty much the entire skeleton, and a remarkable geological context indicative of intentional disposal of the dead (but certainly not homicide, grumble grumble grumble…). The end of 2015 saw the announcement and uproar (often quite sexist) over this amazing sample. You can expect to see more, positive things about this amazing animal in 2016.
We’ll be presenting a bunch about Homo naledi at this year’s AAPA meeting in Hotlanta. I for one will be discussing dental development at Dinaledi- here’s a teaser:
As long as we’re talking about the AAPA meetings, my colleague David Pappano and I are organizing a workshop, “Using the R Programming Language for Biological Anthropology.” Details to come!
Lemur graveyard
Homo naledi wasn’t the only miraculously copious primate sample announced in 2015. Early last year scientists also reported the discovery of an “Enormous underwater fossil graveyard,” containing fairly complete remains of probably hundreds of extinct lemurs and other animals. As with Homo naledi, such a large sample will reveal lots of critical information about the biology of these extinct species.
Australopithecus deyiremeda
Extended Figure 1h from Haile-Selassie et al. (2015), compared with Demirjian developmental stages 6-8 . While the M1 roots look like stage 8 (complete), M2 looks like stage 7 (incomplete).
We also got a new species of australopithecus last year. Australopithecus deyiremeda had fat mandibles, a relatively short face (possibly…), and smaller teeth than in contemporaneous A. afarensis. One tantalizing thing about this discovery is that we may finally be able to put a face to the mysterious foot from Burtele, since these fossils come from nearby sites of about the same geological age. Also intriguing is the possible evidence, based on published CT images (above), that A. deyiremeda had relatively advanced canine and delayed molar development, a pattern generally attributed to Homo and not other australopithecines (if this turns out to be the case, you heard it here first!).
Lomekwian stone tool industry
3D scan and geographical location of Lomekwian tools. From africanfossils.org.
Roughly contemporaneous with A. deyiremeda, Harmand et al. (2015) report the earliest known stone tools from the 3.3 million year old site of Lomekwi 3 in Kenya. These tools are a bit cruder and much older than the erstwhile oldest tools, the Oldowan from 2.6 million years ago. These Lomekwian tools, and possible evidence for animal butchery at the 3.4 million year old Dikika site in Ethiopia (McPherron et al. 2010; Thompson et al. 2015), point to an earlier origin of lithic technology. Fossils attributed to Kenyanthropus platyops are also found at other sites at Lomekwi. With hints at hominin diversity but no direct associations between fossils and tools at this time, a lingering question is who exactly was making and using the first stone tools.
Earliest Homo
The reconstructed Ledi Geraru mandible (top left), compared with Homo naledi (top right), A. deyiremeda (bottom left), and the Uraha early Homo mandible from Malawi (bottom right). Jaws are scaled to roughly the same length from the front to back teeth; the Uraha mandible does not have an erupted third molar whereas the others do and are fully adult.
Just as Sonia Harmand and colleagues pushed back the origins of technology, Brian Villmoare et al. pushed back the origins of the genus Homo, with a 2.7 million year old mandible from Ledi Geraru in Ethiopia. This fossil is only a few hundred thousand years younger than Australopithecus afarensis fossils from the nearby site of Hadar. But the overall anatomy of the Ledi Geraru jaw is quite distinct from A. afarensis, and is much more similar to later Homo fossils (see image above). Hopefully 2016 will reveal other parts of the skeleton of whatever species this jaw belongs to, which will be critical in helping explain how and why our ancestors diverged from the australopithecines. (note that we don’t yet have a date for Homo naledi – maybe these will turn out to be older?)
Early and later Homo
Left: modified figures 2-3 from Maddux et al. (2015). Right: modified figures 7 & 13 from Ward et al. (2015). Note that in the right plot, ER 5881 femur head diameter is smaller than all other Homo except BSN 49/P27.
The earlier hominin fossil record wasn’t the only part to be shaken up. A small molar (KNM-ER 51261) and a set of associated hip bones (KNM-ER 5881) extended the lower range of size variation in Middle and Early (respectively) Pleistocene Homo. It remains to be seen whether this is due to intraspecific variation, for example sex differences, or taxonomic diversity; my money would be on the former.
Left: Penghu 1 hemi-mandible (Chang et al. 2015: Fig. 3), viewed from the outside (top) and inside (bottom). Right: Manot 1 partial cranium (Hershkovitz et al. 2015: Fig. 2), viewed from the left (top) and back (bottom).
At the later end of the fossil human spectrum, researchers also announced an archaic looking mandible dredged up from the Taiwan Straits, and a more modern-looking brain case from Israel. The Penghu 1 mandible is likely under 200,000 years old, and suggests a late survival of archaic-looking humans in East Asia. Maybe this is a fossil Denisovan, who knows? What other human fossils are waiting to be discovered from murky depths?
The Manot 1 calvaria looks very similar to Upper Paleolithic European remains, but is about 20,000 years older. At the ESHE meetings, Israel Hershkovitz actually said the brain case compares well with the Shanidar Neandertals. So wait, is it modern or archaic? As is usually the case, with more fossils come more questions.
Crazy dinosaurs
Yi qi was bringing Skeksi back, and its upper limb had a wing-like shape not seen in any other dinosaur, bird or pterosaur. There were a number of other interesting non-human fossil announcements in 2015 (see here and here), proving yet again that evolution is far more creative than your favorite monster movie makers.
What a year – new species, new tool industries, new ranges of variation! 2015 was a great year to be a paleoanthropologist, and I’ll bet 2016 has just as much excitement in store.
References (in order of appearance)
Haile-Selassie, Y., Gibert, L., Melillo, S., Ryan, T., Alene, M., Deino, A., Levin, N., Scott, G., & Saylor, B. (2015). New species from Ethiopia further expands Middle Pliocene hominin diversity Nature, 521 (7553), 483-488 DOI: 10.1038/nature14448
Harmand, S., Lewis, J., Feibel, C., Lepre, C., Prat, S., Lenoble, A., Boës, X., Quinn, R., Brenet, M., Arroyo, A., Taylor, N., Clément, S., Daver, G., Brugal, J., Leakey, L., Mortlock, R., Wright, J., Lokorodi, S., Kirwa, C., Kent, D., & Roche, H. (2015). 3.3-million-year-old stone tools from Lomekwi 3, West Turkana, Kenya. Nature, 521 (7552), 310-315. DOI: 10.1038/nature14464
McPherron, S., Alemseged, Z., Marean, C., Wynn, J., Reed, D., Geraads, D., Bobe, R., & Béarat, H. (2010). Evidence for stone-tool-assisted consumption of animal tissues before 3.39 million years ago at Dikika, Ethiopia. Nature, 466 (7308), 857-860. DOI: 10.1038/nature09248
Thompson, J., McPherron, S., Bobe, R., Reed, D., Barr, W., Wynn, J., Marean, C., Geraads, D., & Alemseged, Z. (2015). Taphonomy of fossils from the hominin-bearing deposits at Dikika, Ethiopia Journal of Human Evolution, 86, 112-135 DOI: 10.1016/j.jhevol.2015.06.013
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Frank Williams and I have a paper coming out shortly, comparing skull growth in Neandertals and humans. We use the resampling-based “grdif” method (see here) to compare an ontogenetic series of 20 non-adult and 20 adult Neandertals with a giant ontogenetic sample of humans. While Neandertal skull growth has been looked at before, the fragmentary nature of the fossil sample has caused most earlier studies to focus either on single traits or relatively few, often reconstructed, non-adult Neandertals. The advantage of grdif is that it incorporates all fossils regardless of their preservation, and provides a statistical comparison of cross-sectional samples.
In general, and unsurprisingly, skull growth is quite similar between humans and Neandertals. They’re closely related groups, after all. Compare grdif statistics, which measure how much two samples differ in growth between age groups, for humans vs. Neandertals (left) and humans vs. Australopithecus robustus (right):
Growth differences (grdif) between humans and Neandertal skulls (left), and human and A. robustus mandibles (right). If two groups undergo the same amount of growth between age groups or stages, grdif equals 0. Positive values mean the fossil group grows more, while negative values mean humans grow more. Left is a figure from the paper, right is from my dissertation.
The Neandertal-human comparison shows much less difference than the australopith-human comparison. In spite of this general similarity between Neandertal and human skull growth, there are some key differences. Many distinct Neandertal traits, such as the extremely broad nasal aperture, appear piecemeal over the course of growth, rather than all at once. Some recent studies using geometric morphometrics have pointed to different patterns of craniofacial growth in Neandertals, but these were limited in needing smaller samples of more complete fossils. While the grdif approach doesn’t have the power to examine complex shape the same way as GM, and doesn’t produce as pretty of pictures, grdif does help fill in the gaps by including even fragmentary fossils. This is important as it helps reveal when during growth anatomical differences between groups appear.
Our paper will be out (hopefully early) in 2016 in American Journal of Physical Anthropology. In the mean time, the basic strategy of grdif is explained in Cofran (2014), and the R code for using this method can be found on my Research page.
Reference Cofran Z (2014). Mandibular development in Australopithecus robustus. American Journal of Physical Anthropology, 154 (3), 436-46 PMID: 24820665
Lawn Chair Anthropology 