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Topics in biological anthropology, with special focus on human evolution, paleontology, and evolutionary developmental biology (evo-devo).

zacharoo
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September 25, 2011
07:07 PM
360 views

Pictures worth thousands of words and dollars

by zacharoo in Lawn Chair Anthropology

Looking into subdural empyema, which is a meningeal infection you don't want, I stumbled upon a study from the roaring 1970s - the glorious Nixon-Ford-Carter years - using computerized axial tomography (hence, CAT scan) to visualize lesions within the skull (Claveria et al. 1976). Nowadays people refer to various similar scanning techniques simply as "CT" (for computed tomography, though this is not exactly the same as magnetic resonance imaging, MRI).It's pretty amazing how medical imaging has advanced in the 35 years since this study. For example, to the right is a CAT scan from Claveria et al. (1976, Fig. 4). These are transverse images ("slices") through the brain case, the top of the images corresponding to the front of the face. You can discern the low-density (darker) brain from the higher density (lighter) bone - the sphenoid lesser wings and dorsum sellae, and petrous pyramids of the temporal bones are especially prominent in the top left image. In the bottom two images you can see a large, round abscess in the middle cranial fossa. Whoa.What makes this medical imaging technique so great is that it allows a view inside of things without having to dissect into them. Of course, the downside is that it relies on radiation, so ethically you can't be so cavalier as to CT scan just any living thing. If I'd been alive in 1976, CAT scanning would've blown my mind. Still, the image quality isn't super great here, there's not good resolution between materials of different densities, hence the grainy images.But since then, some really smart people have been hard at work to come up with new ways to get better resolution from computerized tomography scans, and the results are pretty amazing. To the left is a slice from a synchrotron CT scan of the MH1 Australopithecus sediba skull (Carlson et al. 2011, Supporting on line material, Fig. S10). You're basically seeing the fossil face-to-face ... if someone had cut of the first few centimeters of the fossil's face. Just like the movie Face Off.Quite a difference from the image above. Here, we can distinguish fossilized bone from the rocky matrix filling in the orbit, brain case and sinuses. Synchrotron even distinguishes molar tooth enamel from the underlying dentin (see the square). The post-mortem distortion to the (camera right) orbit is clear. It also looks as though the hard palate is thick and filled with trabecular bone, as is characteristic of robust Australopithecus (McCollum 1999). Interesting...Even more remarkable, the actual histological structure of bone can be imaged with synchrotron imaging. Mature cortical bone is comprised of these small osteons (or Haversian systems), that house bone cells and transmit blood vessels to help keep bone alive and healthy. Osteons are very tiny, submillimetric. To the right is a 3D reconstruction of an osteon and blood vessels, from synchrotron images (Cooper et al. 2011). The scale bar in the bottom right is 250 micrometers. MICROmeters! Note the scan can distinguish the Haversian canal (red part in B-C) from vessels (white part in B). Insane!Not only has image quality improved over the past few decades, but CT scanning is being applied outside the field of medicine for which it was developed; it's becoming quite popular in anthropology. What I'd like to do, personally, with such imaging is see if it can be used to study bone morphogenesis - if it can be used to distinguish bone deposition vs. resorption, and to see how these growth fields are distributed across a bone during ontogeny. This could allow the study the proximate, cellular causes of skeletal form, how this form arises through growth and development. If it could be applied to fossils, then we could potentially even see how these growth fields are altered over the course of evolution: how form evolves.ReferencesCarlson KJ, Stout D, Jashashvili T, de Ruiter DJ, Tafforeau P, Carlson K, & Berger LR (2011). The endocast of MH1, Australopithecus sediba. Science (New York, N.Y.), 333 (6048), 1402-7 PMID: 21903804Claveria, L., Boulay, G., & Moseley, I. (1976). Intracranial infections: Investigation by computerized axial tomography Neuroradiology, 12 (2), 59-71 DOI: 10.1007/BF00333121Cooper, D., Erickson, B., Peele, A., Hannah, K., Thomas, C., & Clement, J. (2011). Visualization of 3D osteon morphology by synchrotron radiation micro-CT Journal of Anatomy, 219 (4), 481-489 DOI: 10.1111/j.1469-7580.2011.01398.xMcCollum, M. (1999). The Robust Australopithecine Face: A Morphogenetic Perspective Science, 284 (5412), 301-305 DOI: 10.1126/science.284.5412.301... Read more »

Carlson KJ, Stout D, Jashashvili T, de Ruiter DJ, Tafforeau P, Carlson K, & Berger LR. (2011) The endocast of MH1, Australopithecus sediba. Science (New York, N.Y.), 333(6048), 1402-7. PMID: 21903804

Claveria, L., Boulay, G., & Moseley, I. (1976) Intracranial infections: Investigation by computerized axial tomography. Neuroradiology, 12(2), 59-71. DOI: 10.1007/BF00333121

Cooper, D., Erickson, B., Peele, A., Hannah, K., Thomas, C., & Clement, J. (2011) Visualization of 3D osteon morphology by synchrotron radiation micro-CT. Journal of Anatomy, 219(4), 481-489. DOI: 10.1111/j.1469-7580.2011.01398.x

McCollum, M. (1999) The Robust Australopithecine Face: A Morphogenetic Perspective. Science, 284(5412), 301-305. DOI: 10.1126/science.284.5412.301

September 18, 2011
09:06 PM
843 views

[insert clever quip about australopithecus hips]

by zacharoo in Lawn Chair Anthropology

A week and a half ago, Kibii and colleagues (2011) published reconstructions and re-analyses of two hips belonging to the 1.98 million-year old Australopithecus sediba. As with many fossil discoveries, these additions to the fossil record raise more questions than they answer. Unless the question was, "did A. sediba have a pelvis?" It did. Here's a good summary from the paper itself:Thus, Au. sediba is australopith-like in having a long superior pubic ramus and an anteriorly positioned and indistinctly developed iliac pillar...[and] Homo-like in having vertically oriented and sigmoid shaped iliac blades, more robust ilia, and a narrow tuberoacetabular sulcus...and the pubic body is upwardly rotated as in Homo. (p. 1410, emphases mine)So far as I can tell, the main way the hips are 'advanced' toward a more human-like condition is that the iliac blades are more upright and sweep forward more than in earlier known hominid hips. Here's the figure 2 from the paper (more sweet pics of the fossils are available here). NB that in both A. sediba hips much of the upper portions of the iliac blades are missing (reconstructed in white; this region is missing in lots of fossils), so it's possible they were more flaring like the australopith in the center photo.The authors' bottom-line, take-home point is that the A. sediba pelvis has features traditionally associated with large-brained Homo - but belonged to a small-brained species (based solely on the ~430 cc MH1 endocast). They argue that this means that many of these unique pelvic features did not evolve in the context of birthing large-brained babies, as has often been thought. They state that these features are thus "most parsimoniously attributed to altered biomechanical demands on the pelvis in locomotion," and suggest that this hypothetical locomotion was mostly bipedalism but with a good degree of climbing. Maybe, maybe not. This interpretation is consistent with the analysis of the A. sediba foot/ankle (Zipfel et al. 2011).The weird mix of ancient (australopith-like) and newer (Homo-like) pelvic features in A. sediba really raises the question of how australopithecines moved around. More intriguing is that the A. sediba pelvis has different Homo-like features than the ~1 million year old Busidima pelvis (Simpson et al. 2008), which has been attributed to Homo erectus (largely in aspects of the iliac blades). This raises the question of whether A. sediba is really pertinent to the origins of the genus Homo, and whether the Busidima pelvis belongs to Homo erectus or a late-surviving robust australopithecus (e.g. boisei, Ruff 2010).Also interesting is that the subpubic angle (in the pic above, the upside-down "V" created by the pubic bones just above the red labels) is pretty low in MH2. This is curious because modern human males and females differ in how large this angle is - females tend to have a large angle which contributes to an enlarged birth canal, whereas males have a low angle like MH2. But MH2 is considered female based on skeletal and dental size. This raises the additional questions of whether human-like sexual dimorphism had not evolved in hominids prior to 1.9 million years ago, and whether the sex of MH2 was accurately described.Finally, though the authors did a great job comparing this pelvis with those from other hominids, I think a major, more comprehensive comparative review of hominid pelves is in order. How does the older A. afarensis hip from Woranso (Haile-Selassie et al. 2010) inform australopithecine pelvic evolution? What about the possibly-contemporary-maybe-later hip from the nearby site of Drimolen (Gommery et al. 2002)? Given the subadult status of the MH1 individual, it would be interesting to compare with the WT 15000 Homo erectus fossils, or A. africanus subadults from Makapansgat, to examine the evolution of pelvic growth.Lots of interesting questions arise from these fascinating new fossils. "The more you know," right?ReferencesGommery, D. (2002). Description d'un bassin fragmentaire de Paranthropus robustus du site Plio-Pléistocène de Drimolen (Afrique du Sud)A fragmentary pelvis of Paranthropus robustus of the Plio-Pleistocene site of Drimolen (Republic of South Africa) Geobios, 35 (2), 265-281 DOI: 10.1016/S0016-6995(02)00022-0Haile-Selassie Y, Latimer BM, Alene M, Deino AL, Gibert L, Melillo SM, Saylor BZ, Scott GR, & Lovejoy CO (2010). An early Australopithecus afarensis postcranium from Woranso-Mille, Ethiopia. Proceedings of the National Academy of Sciences of the United States of America, 107 (27), 12121-6 PMID: 20566837Kibii, J., Churchill, S., Schmid, P., Carlson, K., Reed, N., de Ruiter, D., & Berger, L. (2011). A Partial Pelvis of Australopithecus sediba Science, 333 (6048), 1407-1411 DOI: 10.1126/science.1202521Ruff, 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... Read more »

Gommery, D. (2002) Description d'un bassin fragmentaire de Paranthropus robustus du site Plio-Pléistocène de Drimolen (Afrique du Sud)A fragmentary pelvis of Paranthropus robustus of the Plio-Pleistocene site of Drimolen (Republic of South Africa). Geobios, 35(2), 265-281. DOI: 10.1016/S0016-6995(02)00022-0

Haile-Selassie Y, Latimer BM, Alene M, Deino AL, Gibert L, Melillo SM, Saylor BZ, Scott GR, & Lovejoy CO. (2010) An early Australopithecus afarensis postcranium from Woranso-Mille, Ethiopia. Proceedings of the National Academy of Sciences of the United States of America, 107(27), 12121-6. PMID: 20566837

Kibii, J., Churchill, S., Schmid, P., Carlson, K., Reed, N., de Ruiter, D., & Berger, L. (2011) A Partial Pelvis of Australopithecus sediba. Science, 333(6048), 1407-1411. DOI: 10.1126/science.1202521

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., Quade, J., Levin, N., 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

Zipfel, B., DeSilva, J., Kidd, R., Carlson, K., Churchill, S., & Berger, L. (2011) The Foot and Ankle of Australopithecus sediba. Science, 333(6048), 1417-1420. DOI: 10.1126/science.1202703

September 12, 2011
11:24 PM
675 views

Test Tossed Tyrone

by zacharoo in Lawn Chair Anthropology

What's the secret to becoming a good father? What would William Cosby do?I for one have no idea BUT! a study published today in PNAS early edition finds an association between studly vs. paternal behavior, and levels of everyone's favorite hormone, testosterone (T).Using longitudinal data, researchers (Gettler et al. in press) found that, in general, a young guy with higher levels of circulating T is more likely than a guy with low T to become a father w/in a few years. MOREOVER! this erstwhile-high-T-and-now-father then experiences a relatively sharper decrease in T than would be expected simply because of aging. PLUS! fathers who interacted with their kids on a daily basis had lower T than fathers who didn't hang around their kids too often.One thing neat about this study is that it uses longitudinal instead of cross-sectional data. A cross-sectional version of this study would've sampled a bunch of dudes (hopefully somewhat randomly) only once. This can be problematic because it's then hard to interpret the results in light of the many sources of variation between people. This study, on the other hand, sampled a tonne (n = 694) of guys at more than one occasion, so they can tell how individuals' testosterone levels tend to change in paternal vs. free-spirited circumstances.The last line of the paper is pretty intriguing: "[these results] add to the evidence that human males have an evolved neuroendocrine architecture shaped to facilitate their role as fathers and caregivers as a key component of reproductive success." (Gettler et al. in press: p. 5/6) This is especially interesting in light of the Ardipithecus ramidus-related evidence for a great antiquity of humans' paternal proclivity (Lovejoy 1981, Lovejoy et al. 2009). Just how and why testosterone responds to/mediates this fatherly 'reproductive strategy' is mysterious to me. And of course, linking this hormonal phenomenon with anything as old as Ardi is a challenge I'm certainly not up to. Still neat, though.My personal circulating T levels are consistently through the roof. So in the event that I become a father, it will be interesting to see if the subsequent, astronomical hormone drop, predicted by this study, won't cause my entire body to collapse in on itself.ReferenceGettler LT et al. in press. Longitudinal evidence that fatherhood decreases testosterone in human males. Proceedings of the National Academy of Sciences... doi: 10.1073/pnas.1105403108Lovejoy, C. (1981). The Origin of Man Science, 211 (4480), 341-350 DOI: 10.1126/science.211.4480.341Lovejoy CO (2009). Reexamining human origins in light of Ardipithecus ramidus. Science (New York, N.Y.), 326 (5949), 740-8 PMID: 19810200Photo credit: google (image) "Bill Cosby Fatherhood"... Read more »

Lovejoy, C. (1981) The Origin of Man. Science, 211(4480), 341-350. DOI: 10.1126/science.211.4480.341

Lovejoy CO. (2009) Reexamining human origins in light of Ardipithecus ramidus. Science (New York, N.Y.), 326(5949), 740-8. PMID: 19810200

August 31, 2011
04:40 PM
729 views

How old is the Acheulian tool industry and why does it matter?

by zacharoo in Lawn Chair Anthropology

Two views of an Acheulian handaxe adorn the cover of this week's Nature (right). Always happy to see paleoanthropology stuff be classy, front-page news. The cover highlights Christopher Lepre's and colleagues' announcement of what may be the oldest Acheulian tools known.
To recap stone tools: The first good evidence of tool use by humans' ancestors are the Oldowan lithics from the 2.6 million year old site of Gona in Ethiopia (Semaw et al. 2003). McPherron and others (2010) reported 2 possibly-cut-marked animal bones from the 3.4 million-year old site of Dikika; but this latter evidence is a bit too scant for us to really be sure our ancestors had adopted technology this early. Anyway, the Oldowan was a very basic tool industry, consisting largely of crude flakes taken off cobbles. It may sound lame, but even the most basic stone-tool-making requires some skills, trust me, it's kinda hard. So stone tools appear roughly 2.5 million years ago, which is also about the time that we have fossils that might document the earliest members of our genus Homo. Sweet.
The legend goes that the next technological revolution doesn't come until about 1 million years later - until around 1.5 million years ago, stone tools were quite basic. But after a while we start seeing these "handaxes" or "bifaces" (cuz flakes are removed from both of the core's faces; see above) that have become kind of the hallmark of what's termed the Acheulian industry. I'm sure there are other key indicators but what do I know, I'm not an archaeologist. Arguably, the rise of the Acheulian from its humble Oldowan beginnings is a milestone in human cognitive evolution - a more complex tool should require a more complex brain, right? Lepre and team announced today that they have some Acheulian handaxes from the Kenyan site of Kokiselei-4, dating to 1.76 million years ago. The authors draw two conclusions: 1) the Acheulian (and thereby more advanced cognition) is a few hundred thousand years older than previously thought, and 2) the co-occurrence of Acheulian and Oldowan tools at this time indicates the presence of contemporaneous human species with different cognitive capabilities.
Now what's a bit odd here is that the presence of handaxes among otherwise Oldowan assemblages is not a new or unique thing. In her archaeological research at Olduvai Gorge in Tanzania, Mary D Leakey distinguished some assemblages as "Developed Oldowan." Here's a relevant blurb from a study by Y. Kimura (2002: 292-293):"Leakey recognized two distinctive industries, Oldowan and Acheulian, from Bed I through Bed III at Olduvai. The former was characterized by the presence of various choppers and attributed to Homo habilis sensu lato, whereas the latter was traditionally defined to contain bifaces more than 40-60% of the tools, and attributed to H. erectus sensu lato.The Oldowan was then classified into Oldowan (1.87-1.65 mya) and Developed Oldowan (1.65-0.6 mya) based on the increased light-duty tools, spheroids and bifaces in the latter. The Developed Oldowan coexisted with Acheulian" (emphasis mine)So the co-occurrence of Oldowan (i.e. choppers) and Acheulian (some handaxes) is known from other sites, albeit not until around 1.5 million years ago. Too bad I'm not an archaeologist nor know more about lithics, because I wish I could put the new Kokiselei-4 assemblage into this context - just how is it different from "Developed Oldowan"? As John Hawks pointed out before I did, "developed Oldowan" doesn't appear in the Lepre et al. discussion. Hrm. Then they make this statement:"Homo erectus is traditionally thought to be the first hominin to disperse from Africa, yet the oldest known out-of-Africa fossil hominin sites lack stone tools or preserve only Oldowan-style artefacts. ... Our data indicate that the earliest development of the Acheulian occurred in Africa at 1.76 [million years] ago and was contemporaneous with or perhaps pre-dated the earliest hominin dispersals into Eurasia (Lepre et al. 2011: 84).They then go on to suggest that two contemporaneous species lived in Africa in the early Pleistocene - one of these species invented the Acheulian and stayed in Africa, while the other species was too dumb to make anything beyond Oldowan, and instead these dullards left Africa to colonize the rest of the world. This silly scenario seems to stem from an under-appreciation of what Dmanisi demonstrates (possibly since the recent dating paper by Reed Ferring and others only came out a few months ago, probably after the Lepre et al. paper was in press). The Dmanisi fossils establish that hominins more primitive than later Homo erectus (Rightmire et al. 2006) had dispersed into Eurasia by around 1.85 million years ago (if not earlier), with mere Oldowan technology (Mgeladze et al. 2010, Ferring et al. 2011). So Lepre et al.'s claim that the earliest Acheulian "was contemporaneous or perhaps pre-dated" the first out-of-Africa dispersals just isn't true. And without that, there's no support for the silly scenario of a smart, techno-savvy but stationary species being contemporaneous with a colonizing but less crafty-and-cunning species.
It's really cool if the Kokiselei-4 tools truly represent the earliest record of the Acheulian. But, it should be clear by now that we can't simply equate technology and taxonomy. So how old is the Acheulian and why does it matter? I'm fine with a 1.76 million year date, but I also don't think it matters too much. (sorry to be so Dmanisi-centric)

ReferencesFerring, R., Oms, O., Agusti, J., Berna, F., Nioradze, M., Shelia, T., Tappen, M., Vekua, A., Zhvania, D., & Lordkipanidze, D. (2011). From the Cover: Earliest human occupations at Dmanisi (Georgian Caucasus) dated to 1.85-1.78 Ma Proceedings of the National Academy of Sciences, 108 (26), 10432-10436 DOI: 10.1073/pnas.1106638108
Kimura, Y. (2002). Examining time trends in the Oldowan technology at Beds I and II, Olduvai Gorge Journal of Human Evolution, 43 (3), 291-321 DOI: 10.1006/jhev.2002.0576
Lepre, C., Roche, H., Kent, D., Harmand, S., Quinn, R., Brugal, J., Texier, P., Lenoble, A., & Feibel, C. (2011). An earlier origin for the Acheulian Nature, ... Read more »

Ferring, R., Oms, O., Agusti, J., Berna, F., Nioradze, M., Shelia, T., Tappen, M., Vekua, A., Zhvania, D., & Lordkipanidze, D. (2011) From the Cover: Earliest human occupations at Dmanisi (Georgian Caucasus) dated to 1.85-1.78 Ma. Proceedings of the National Academy of Sciences, 108(26), 10432-10436. DOI: 10.1073/pnas.1106638108

Kimura, Y. (2002) Examining time trends in the Oldowan technology at Beds I and II, Olduvai Gorge. Journal of Human Evolution, 43(3), 291-321. DOI: 10.1006/jhev.2002.0576

Lepre, C., Roche, H., Kent, D., Harmand, S., Quinn, R., Brugal, J., Texier, P., Lenoble, A., & Feibel, C. (2011) An earlier origin for the Acheulian. Nature, 477(7362), 82-85. DOI: 10.1038/nature10372

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

Mgeladze, A., Lordkipanidze, D., Moncel, M., Despriee, J., Chagelishvili, R., Nioradze, M., & Nioradze, G. (2011) Hominin occupations at the Dmanisi site, Georgia, Southern Caucasus: Raw materials and technical behaviours of Europe’s first hominins. Journal of Human Evolution, 60(5), 571-596. DOI: 10.1016/j.jhevol.2010.10.008

Rightmire, G., Lordkipanidze, D., & Vekua, A. (2006) Anatomical descriptions, comparative studies and evolutionary significance of the hominin skulls from Dmanisi, Republic of Georgia. Journal of Human Evolution, 50(2), 115-141. DOI: 10.1016/j.jhevol.2005.07.009

Semaw, S., Rogers, M., Quade, J., Renne, P., Butler, R., Dominguez-Rodrigo, M., Stout, D., Hart, W., Pickering, T., & Simpson, S. (2003) 2.6-Million-year-old stone tools and associated bones from OGS-6 and OGS-7, Gona, Afar, Ethiopia. Journal of Human Evolution, 45(2), 169-177. DOI: 10.1016/S0047-2484(03)00093-9

August 24, 2011
05:13 PM
748 views

Back to the backbone of Homo erectus

by zacharoo in Lawn Chair Anthropology

Of course the title is referring to all of the back bones. An alternate title may be "The backbone's connected to the - what bone?" but that's also kinda lame. I'll do better next time.
Martin Hausler and colleagues (in press) report on newly identified vertebral fragments of the WT 15000 Homo erectus skeleton, perhaps the most complete of an early hominid (this one ~1.5 million years ago). This skeleton, and other early hominids (i.e. Australopithecus africanus), were described as having six lumbar (lower back) vertebrae; the modal number in humans is 5, and 3-4 in the great apes. The issue of vertebral formula (the number of cervical, thoracic, lumbar, and sacral verts) in hominids is interesting because it is unclear what the ancestral condition is: was ancestral pattern to have more lumbars (like australopiths) from which humans and apes lost verts, or is ape pattern is ancestral, and lumbars were gained then lost over the course of human evolution.
The fragments found by Hausler and team establish that the WT 15000 individual - and presumably all H. erectus - possessed only 5 lumbar vertebrae. In the past, the only evidence of the 6th-to-last pre-sacral vertebra was the vertebral body. It was unclear whether this vertebra would have had articular facets for ribs (like a thoracic vertebra) or not (like a lumbar vertebra). The pedicle fragments identified by Hausler and colleagues (figure to the right) have a rib facet, and so indicate that the 6th-to-last vertebra of this skeleton was thoracic. Thus, WT 15000 - and again presumably all Homo erectus - had a modern-human-like vertebral formula.
The evolution of the hominid spinal column is interesting. Hausler and team's results don't refute the hypothesis that the ancestral vertebral formula was higher than in modern great apes. The hypothesis of 5 lumbars in the great ape-human common ancestor, which became reduced independently in the Great ape lineages. The evo-devo of the spinal column is especially interesting because it seems to me that it may not be so outlandish to identify and test hypotheses about how spinal column development (segmentation) changed over the course of hominid and ape evolution. I need to think on this a bit, I'll hafta get back to you . . .* figures are from Hausler et al. in press
ReferenceMartin Haeusler, Regula Schiess, Thomas Boeni (2011). New vertebral and rib material point to modern bauplan of the Nariokotome Homo erectus skeleton Journal of Human Evolution : 10.1016/j.jhevol.2011.07.004... Read more »

Martin Haeusler, Regula Schiess, Thomas Boeni. (2011) New vertebral and rib material point to modern bauplan of the Nariokotome Homo erectus skeleton. Journal of Human Evolution. info:/10.1016/j.jhevol.2011.07.004

August 21, 2011
07:37 AM
368 views

eFfing Fossil Friday (another late edition)

by zacharoo in Lawn Chair Anthropology

I'm sitting at a cafe in Tbilisi, departing at 4:00 am tomorrow for America. Readers will notice that I've been MIA while working with the second annual Dmanisi Paleoanthropology Field School. I hate to say it but I'm glad I was too busy to blog all the goings-on (though sorry if it disappointed anyone). All in all it was another great year, and we found some great fossils (about which I don't think I have permission to say anything at all). Here's this year's class with their certification of badassery at the site on the last day:But Dmanisi won't be the subject of this belated eFfing Fossil Friday. I'd like instead to turn to the question of just what fossils are good for. I'm told that in China, fossil teeth were once interpreted as dragons' teeth, and so pulverized and sold as medicine. But what good are they to non-medical science? My recent research interests have come to focus on the relationship between evolution and development. Evolutionary developmental biology ("evo-devo") research has been dominated by studies of genes, gene expression, and model organisms like fruit flies and mice. In such an environment, the question of the relevance of fossils is especially poignant.
But this morning, while planning a human evo-devo course I hope to teach next summer, I stumbled upon a review paper by Rudolf Raff, titled "Written in Stone: Fossils, genes and evo-devo" (2007). I think the abstract sums things up pretty well:Fossils give evo-devo a past. They inform phylogenetic trees to show the direction of evolution of developmental features, and they can reveal ancient body plans. Fossils also provide the primary data that are used to date past events, including divergence times needed to estimate molecular clocks, which provide rates of developmental evolution. Fossils can set boundaries for hypotheses that are generated from living developmental systems, and for predictions of ancestral development and morphologies. Finally, although fossils rarely yield data on developmental processes directly, informative examples occur of extraordinary preservation of soft body parts, embryos and genomic information.It seems often that fossils are falling by the wayside. There's a sentiment that there's not much information to be gotten from fossils - they're too incomplete, too few, too inconvenient, at least as compared with extremely high-output data such as that coming from genomics. But Raff is right - we need fossils. Beyond the excellent points Raff raises in the review, I'm working on getting the most out of these seemingly data-poor fossil samples. Because modern computers are so powerful nowadays, I'm using their sheer processing power to test hypotheses about growth and development in fossil samples. These battered bunches of bones are too tiny to be analyzed by traditional methods. But one thing I think is important to take away from this computer-crazy Information Age, is that we now have machines that can handle almost any kind of question one can think to ask, and it's really inspiring. The sequencing and analyses of ancient Neandertal and Denisova genomes (Green et al. 2010, Reich et al. 2010) are excellent examples of the amazing research that can be done with computers and creativity (and probably also a horde of hard-working math majors).
So this eFFF (or Sunday) is not dedicated to any specific fossil or set of fossils, but rather to all fossils, even the crappy fragments. Gaumarjos, fossils: your secrets are not safe from us.
ReferenceGreen, R., Krause, J., Briggs, A., Maricic, T., Stenzel, U., Kircher, M., Patterson, N., Li, H., Zhai, W., Fritz, M., Hansen, N., Durand, E., Malaspinas, A., Jensen, J., Marques-Bonet, T., Alkan, C., Prufer, K., Meyer, M., Burbano, H., Good, J., Schultz, R., Aximu-Petri, A., Butthof, A., Hober, B., Hoffner, B., Siegemund, M., Weihmann, A., Nusbaum, C., Lander, E., Russ, C., Novod, N., Affourtit, J., Egholm, M., Verna, C., Rudan, P., Brajkovic, D., Kucan, Z., Gusic, I., Doronichev, V., Golovanova, L., Lalueza-Fox, C., de la Rasilla, M., Fortea, J., Rosas, A., Schmitz, R., Johnson, P., Eichler, E., Falush, D., Birney, E., Mullikin, J., Slatkin, M., Nielsen, R., Kelso, J., Lachmann, M., Reich, D., & Paabo, S. (2010). A Draft Sequence of the Neandertal Genome Science, 328 (5979), 710-722 DOI: 10.1126/science.1188021
Raff, R. (2007). Written in stone: fossils, genes and evo–devo Nature Reviews Genetics, 8 (12), 911-920 DOI: 10.1038/nrg2225
... Read more »

Raff, R. (2007) Written in stone: fossils, genes and evo–devo. Nature Reviews Genetics, 8(12), 911-920. DOI: 10.1038/nrg2225

Green, R., Krause, J., Briggs, A., Maricic, T., Stenzel, U., Kircher, M., Patterson, N., Li, H., Zhai, W., Fritz, M.... (2010) A Draft Sequence of the Neandertal Genome. Science, 328(5979), 710-722. DOI: 10.1126/science.1188021

Reich D, Green RE, Kircher M, Krause J, Patterson N, Durand EY, Viola B, Briggs AW, Stenzel U, Johnson PL.... (2010) Genetic history of an archaic hominin group from Denisova Cave in Siberia. Nature, 468(7327), 1053-60. PMID: 21179161

July 20, 2011
12:54 PM
342 views

New beef with boisei - maybe the dingo ate their babies?

by zacharoo in Lawn Chair Anthropology

Unfortunately, the title is not in reference to a study demonstrating that early hominids fell prey to wild dogs. But Elaine Benes would have appreciated it.
As part of my Latitudes Tour, I'm in Nairobi for a couple of days, hoping to spend some quality time with the young Australopithecus boisei kids at the Nairobi National Museum. Recall (that is, if I've mentioned it here?) that my dissertation research is on growth of the lower jaw, in Australopithecus robustus as compared to modern humans. The study of growth obviously requires analyzing individuals across different age groups (an "ontogenetic series" is the fancy term). Admittedly, then, the focus on A. robustus is chiefly because this species has the largest ontogenetic sample of any early hominid (tho at nearly 15 subadults, it's still not as large as one could hope). Also because A. robustus was totally badass.
Australopithecus boisei makes an important comparison for A. robustus, because the two species are allegedly evolutionary 'sisters' - the "robust" australopithecines (though I'm personally not convinced that these two are each other's closest relative). So their growth should be pretty similar. At the same time, though, A. boisei shows much greater adaptations to heavy chewing - they've been referred to as "hyper-robust." So comparing growth in these species should elucidate how their differences arise.
Problem is, there just aren't enough kids! It's like that song by Arcade Fire. Wood and Constantino (2007) published a pretty comprehensive review of A. boisei, including a 1.5-page table of the skulls and teeth attributed to the species. So far as I know, only 4 specimens in this table are subadult mandibles, and so far as I can tell, they're all about the same age (right around the age that the first permanent molar comes in). There are so many jaws of adult A. boisei (although many of these are abraded mandibular bodies lacking teeth) - so how can there be fewer subadults?!?!
A very preliminary observation of infant-child pairs in the two species suggests they both increase in size fairly dramatically between when they only have baby (a.k.a. "deciduous" or "milk") teeth and when the first permanent molar comes in. But this is just a preliminary observation based on 2 specimens of each species! Take with a grain of salt!
On second thought, maybe I'll propose the nearly untestable hypothesis that bone-eating hyenas ate the boisei babes, and that's why we don't have their jaws. What could have been nicely preserved subadult boisei bones are instead coprolites (fossilized poops). A little spectacular, yes, but it's also been hypothesized that many of the A. robustus fossils we know and love came to us as carnivores' scraps.
further reading:Wood, B., & Constantino, P. (2007). Paranthropus boisei: Fifty years of evidence and analysis American Journal of Physical Anthropology, 134 (S45), 106-132 DOI: 10.1002/ajpa.20732... Read more »

Wood, B., & Constantino, P. (2007) Paranthropus boisei: Fifty years of evidence and analysis. American Journal of Physical Anthropology, 134(S45), 106-132. DOI: 10.1002/ajpa.20732

June 27, 2011
04:08 PM
404 views

Bloodsport in Australopithecus africanus?

by zacharoo in Lawn Chair Anthropology

A few months ago in a post about the ilium and cannibals, I relayed a quote by Dr. Raymond Dart who was the first to recognize (and name) the hominid genus Australopithecus, back in 1925. I'd also mentioned that he was described [in a reference that escapes me] as "blood-thirsty." This macabre descriptor came to mind again, as I'm reading his (1948) description of the MLD 2 mandible, of a juvenile A. africanus from Makapansgat cave in South Africa (figure is from the paper):"[Individuals represented by MLD2 and another skull fragment] met their death by manually applied violence. The fractures exhibited by the mandible show that the violence, which probably occurred in fatal combat, was a localized crushing impact received by the face slightly to the left of the midline in the incisor region, and administered presumably by a bludgeon... this youth probably met his fate at the hands of a kinsman more expert than himself in the accurate application of directed implements" (p. 393-394)This rather fanciful hypothesis may reflect Dart's alleged bloodlust, and the condition of the fossil likely reflects damage that occurred after death during the sometimes abusive process of fossilization.
ReferenceDart, R. (1948). The adolescent mandible of Australopithecus prometheus American Journal of Physical Anthropology, 6 (4), 391-412 DOI: 10.1002/ajpa.1330060410... Read more »

Dart, R. (1948) The adolescent mandible of Australopithecus prometheus. American Journal of Physical Anthropology, 6(4), 391-412. DOI: 10.1002/ajpa.1330060410

June 8, 2011
02:45 PM
395 views

Earliest human migrations

by zacharoo in Lawn Chair Anthropology

One of my favorite paleoanthropological sites is Dmanisi, in the Republic of Georgia. It is the oldest securely dated hominid site outside Africa (just under 1.85 million years ago), and the hominids found there display a neat mix of primitive Homo habilis and derived H. erectus features. I consider myself lucky to have had the opportunity to excavate at Dmanisi last year, and to return to Georgia (lamazi Sakartvelo! [I hope I translated that correctly]) for more fieldwork next month.
Recently, Reid Ferring and others (2011) described the results of excavations of M5, a section of the site a bit aways from the area where the hominids were found. M5 is pretty cool because it presents a nice geological "layer cake," as Ferring described it to us: each of the strata (different layers of deposition) are nicely and evenly stacked on one another. Check out the labeled layers on the right of the figure, from Ferring et al. 2011:This is in stark contrast to the jumbled strata (like 'spaghetti') where the hominids were found. In geology and archaeology, there is a general "law of superposition," which states that the lowest layers in a sequence would have been deposited earlier than the layers above them. The A sediments at Dmanisi, as seen in the figure above, are thus older than the Bs. Hominids have only been found in the B sediments. But work at M5 has shown that stone tools are found in the older A sediments, meaning that hominids arrived at the site and used it continually, beginning just after 1.85 million years ago.
Tools from the site differ between the older A and slightly later (still older than 1.75 million years!) B sediments in both material and manufacture. As they say in the paper (p. 2/5), a major difference in tool manufacture between the strata A and B occupations could be that during the earlier A times, "either cores were more intensively reduced or selected flakes were made elsewhere and carried to the site." I'm not sure why this may be, but it is neat that within a fairly narrow time span, researchers can see habits change in our early ancestors.
The authors also note that the older tools from A sediments indicate "that Eurasia was probably occupied before Homo erectus appears in the East African fossil record" (from the paper's abstract). If only hominids also came out of the A sediments! The News is touting this as meaning H. erectus evolved in Eurasia and then some members of the 'new species' moved back into Africa, but I don't think this is necessarily the case. The Dmanisi hominids are described as H. erectus, but lack some key H. erectus apomorphies (most notably a large brain size) and really look pretty similar to contemporary hominids in Kenya (such as KNM-ER 3733) and Tanzania (such as OH 16). Plus, the E. African hominid fossil record around 1.9 million years ago leaves some tantalizing hints at hominids more erectus-like than habilis-like, such as the ER 2598 occipital fragment.
So while Dmanisi definitely demonstrates the presence of hominids outside Africa earlier than most well-accepted "Homo erectus" (or "ergaster") fossils in E. Africa, I don't think they necessarily indicate that the species arose in Eurasia. Rather, what the fossil record likely shows is the evolution of populations of early Homo, in Africa and Eurasia, toward the more 'advanced' H. erectus we know and love (due to gene flow w/in a widespread species, rather than parallel evolution of similar traits in different species).
ReferenceFerring R, Oms O, Agustí J, Berna F, Nioradze M, Shelia T, Tappen M, Vekua A, Zhvania D, & Lordkipanidze D (2011). Earliest human occupations at Dmanisi (Georgian Caucasus) dated to 1.85-1.78 Ma. Proceedings of the National Academy of Sciences of the United States of America PMID: 21646521... Read more »

Ferring R, Oms O, Agustí J, Berna F, Nioradze M, Shelia T, Tappen M, Vekua A, Zhvania D, & Lordkipanidze D. (2011) Earliest human occupations at Dmanisi (Georgian Caucasus) dated to 1.85-1.78 Ma. Proceedings of the National Academy of Sciences of the United States of America. PMID: 21646521

May 27, 2011
02:14 PM
923 views

Culinary trends in an extinct hominid

by zacharoo in Lawn Chair Anthropology

A few weeks ago I discussed a recent paper that analyzed the carbon and oxygen isotope ratios from Australopithecus boisei molars (Cerling et al. 2011). The major finding here was that an enlarged sample (n=24 more) corroborated earlier isotopic (van der Merwe et al. 2008) and tooth wear evidence (Ungar et al. 2008) that A. boisei probably did not subsist on as much hard foods as previously thought. Although this strange hominid probably ate mostly grass/aquatic tubers, some researchers think it may have looked something like this:Left, A. boisei reconstructed skull, from McCollum (1999, Fig. 1). Right, artist's reconstruction of what the individual on the left may have looked like during life.But looking at the numbers I'm wondering if the carbon isotopes reveal anything more about this curious hominid. If we plot boisei's carbon 13 values against the fossils' estimated age, there's a small hint of a temporal trend, of increasing carbon 13 levels over time (more C4 plant consumption). Fitting a line to these data does indicate an increasing C4 component over time, but the slope of the line is not significantly different from zero. The early, high value could be an outlier (not eating the same stuff as his/her peers?), although the lowest carbon 13 value of all that would support this trend is also much lower than the other values; it could be a more anomalous one. So while it's tempting to hypothesize dietary change over time in A. boisei, at the moment it looks like you can't reject the hypothesis that diet is consistent throughout the Pleistocene until the A. boisei's demise.In addition, Cerling and colleagues sampled at least one of each of the cheek teeth. Because teeth form in the jaws in a sequence (not all at the exact same time), the isotopic signatures from given teeth represent the dietary intake of carbon at certain different points in an individual's childhood. In the figure below I lumped upper and lower teeth together; the un-numbered "M" indicates molars unassigned to a specific position.The first molar crown starts to form right around birth, and note here that it's carbon 13 values are slightly higher than the other molars. The premolars and second molar start to form around the same time, so it is curious that each of these teeth show distinctly different ranges of carbon 13 levels. The sole P3 is also the lowest value (eating fewer C4 plants) in the entire sample, but the P4 has less negative values (eating more C4 plants). Not sure what's going on here, but maybe later analyses of more specimens will clarify the situation. Supporting dietary stasis, Ungar and colleagues (2008) reported similar molar tooth wear in specimens from 2.27-1.4 million years ago.
Our australopithecine ancestors and cousins have proven to be a rag-tag bunch of funny bipeds, and A. boisei has proven to be one of the weirder ones, in my opinion. Of course descriptions of of Ardipithecus ramidus and Australopithecus sediba skeletons have been recent reminders that we have lots left to learn about Pleistocene hominids. For my part, I'm interested in working out the deal with the group of "robust" Australopithecus.
ReferencesCerling, T., Mbua, E., Kirera, F., Manthi, F., Grine, F., Leakey, M., Sponheimer, M., & Uno, K. (2011). Diet of Paranthropus boisei in the early Pleistocene of East Africa Proceedings of the National Academy of Sciences DOI: 10.1073/pnas.1104627108
McCollum, M. (1999). The Robust Australopithecine Face: A Morphogenetic Perspective Science, 284 (5412), 301-305 DOI: 10.1126/science.284.5412.301
Ungar PS, Grine FE, & Teaford MF (2008). Dental microwear and diet of the Plio-Pleistocene hominin Paranthropus boisei. PloS one, 3 (4) PMID: 18446200
van der Merwe NJ, Masao FT and Bamford MK. 2008. Isotopic evidence for contrasting diets of early hominins Homo habilis and Australopithecus boisei of Tanzania. South African Journal of Science 104: 153-155... Read more »

Cerling, T., Mbua, E., Kirera, F., Manthi, F., Grine, F., Leakey, M., Sponheimer, M., & Uno, K. (2011) Diet of Paranthropus boisei in the early Pleistocene of East Africa. Proceedings of the National Academy of Sciences. DOI: 10.1073/pnas.1104627108

McCollum, M. (1999) The Robust Australopithecine Face: A Morphogenetic Perspective. Science, 284(5412), 301-305. DOI: 10.1126/science.284.5412.301

Ungar PS, Grine FE, & Teaford MF. (2008) Dental microwear and diet of the Plio-Pleistocene hominin Paranthropus boisei. PloS one, 3(4). PMID: 18446200

May 16, 2011
08:41 PM
779 views

Good olde dentistrie

by zacharoo in Lawn Chair Anthropology

I'm reading up on mandibular rotation, which is the change in orientation of the mandibular corpus relative to the rest of the skull during growth (the corpus is the horizontal part of your jaw that holds up your teeth; check out the shape changes in the mandibles in the blog header). So far as I can tell, the original classic paper on the topic is by Bjork (1955). Growth was studied by implanting metal pins into the jaws, then seeing how they move across ontogeny via X-rays (which were once called "roentgenograms," neat-o!) Here's a picture of the procedure, from Bjork (1955):HOLY GOD WHAT DID THAT KID DO TO DESERVE THIS?! And although there must be a third person there, it sorta looks like there's a three-handed dentist wielding a hammer, a nail, and a kid's face. No wonder so many people are afraid of the dentist.

ReferenceBJORK A (1955). Facial growth in man, studied with the aid of metallic implants. Acta odontologica Scandinavica, 13 (1), 9-34 PMID: 14398173... Read more »

BJORK A. (1955) Facial growth in man, studied with the aid of metallic implants. Acta odontologica Scandinavica, 13(1), 9-34. PMID: 14398173

May 9, 2011
08:08 PM
829 views

If imitation is the sincerest form of flattery

by zacharoo in Lawn Chair Anthropology

Life as we know it has taken some strange courses. Of all the things an animal could do with its time, pretending to be an ant is apparently pretty popular. According to a review article in the latest Current Biology, there are probably over 2000 abhorrent species of myrmecomorphs (ant impersonators), including spiders, caterpillars, mites, beetles, and other types of arthropod biodiversity I'm not familiar with, that have come to resemble ants in some form or another.
It's interesting how and why different life forms have come to p-ant-omime. For example, in the picture above, (Maderspacher & Stensmyr 2011, Fig. 3) on the left side is the crab spider (Aphantochilus rogersi) mimicking ant species in the genus Cephalotes - which the spider comes upon unawares and then feeds upon (getting pwned on the right side of the photo). If imitation is the sincerest form of flattery, then mimicry must be the most malevolent means of creepy.
Or here's a treehopper (Cyphonia clavata, an insect and not a spider like above) that doesn't just disguise itself as an ant, but rather has a whole ant-shaped appendage bursting from its back in a disgusting perversion of alien birth in the Alien series (Maderspacher & Stensmyr 2011, Fig. 1). It is quite remarkable that a surprisingly common yearning to be perceived as an ant has resulted in convergent evolution of an ant-ish figure in myriad of nature's more disgusting creations, not to mention in ants themselves.
ReferenceFlorian Maderspacher & Marcus Stensmyr (2011). Myrmecomorphomania Current Biology, 21 (9) : R291-293. doi:10.1016/j.cub.2011.04.006... Read more »

Florian Maderspacher, & Marcus Stensmyr. (2011) Myrmecomorphomania. Current Biology, 21(9). info:/doi:10.1016/j.cub.2011.04.006

May 7, 2011
11:15 AM
444 views

What the hell was Australopithecus boisei doing?

by zacharoo in Lawn Chair Anthropology

A little over 2 million years ago there a major divergence of hominids, leading on the one hand to our earliest ancestors in the genus Homo, and on the other hand to a group of 'robust' australopithecines, the latter group a failed evolutionary experiment in being human. In our ancestors, parts of the skull associated with chewing began to get smaller and more delicate, while the robust australopithecines increased the sizes of their crushin'-teeth and chewin'-muscle attachments...... Read more »

Cerling TE, Mbua E, Kirera FM, Manthi FK, Grine FE, Leakey MG, Sponheimer M, & Uno KT. (2011) Diet of Paranthropus boisei in the early Pleistocene of East Africa. Proceedings of the National Academy of Sciences of the United States of America. PMID: 21536914

McCollum, M. (1999) The Robust Australopithecine Face: A Morphogenetic Perspective. Science, 284(5412), 301-305. DOI: 10.1126/science.284.5412.301

Ungar PS, Grine FE, & Teaford MF. (2008) Dental microwear and diet of the Plio-Pleistocene hominin Paranthropus boisei. PloS one, 3(4). PMID: 18446200

April 25, 2011
10:58 PM
846 views

What big teeth you have indeed

by zacharoo in Lawn Chair Anthropology

If our friend Little Red Riding Hood was dumb enough to've thought a wolf in babushka threads was her grandma, well, she probably would have played Bingo with a grandmother-mimicking Australopithecus anamensis.... Read more »

Kunimatsu, Y., Nakatsukasa, M., Sawada, Y., Sakai, T., Hyodo, M., Hyodo, H., Itaya, T., Nakaya, H., Saegusa, H., Mazurier, A.... (2007) A new Late Miocene great ape from Kenya and its implications for the origins of African great apes and humans. Proceedings of the National Academy of Sciences, 104(49), 19220-19225. DOI: 10.1073/pnas.0706190104

Leakey, M., Feibel, C., McDougall, I., & Walker, A. (1995) New four-million-year-old hominid species from Kanapoi and Allia Bay, Kenya. Nature, 376(6541), 565-571. DOI: 10.1038/376565a0

Ward, C. (2001) Morphology of Australopithecus anamensis from Kanapoi and Allia Bay, Kenya. Journal of Human Evolution, 41(4), 255-368. DOI: 10.1006/jhev.2001.0507

White, T., Suwa, G., & Asfaw, B. (1994) Australopithecus ramidus, a new species of early hominid from Aramis, Ethiopia. Nature, 371(6495), 306-312. DOI: 10.1038/371306a0

White, T., WoldeGabriel, G., Asfaw, B., Ambrose, S., Beyene, Y., Bernor, R., Boisserie, J., Currie, B., Gilbert, H., Haile-Selassie, Y.... (2006) Asa Issie, Aramis and the origin of Australopithecus. Nature, 440(7086), 883-889. DOI: 10.1038/nature04629

April 21, 2011
11:24 AM
458 views

Humans, kinda like rabbits

by zacharoo in Lawn Chair Anthropology

Population size and expansion... Read more »

Hawks, J., Wang, E., Cochran, G., Harpending, H., & Moyzis, R. (2007) Recent acceleration of human adaptive evolution. Proceedings of the National Academy of Sciences, 104(52), 20753-20758. DOI: 10.1073/pnas.0707650104

March 9, 2011
01:35 AM
830 views

Have I uncovered an epigenetic conspiracy?

by zacharoo in Lawn Chair Anthropology

Nope! In an effort to reduce plastic water bottle waste, UM has been installing these badass water fountains around campus that automatically fill a bottle - I suppose it could fill a shoe, too - and tell you how many plastic bottles they've saved you from wasting. I have to say they're pretty convenient...... and repressive? I noticed the contraption is named "EZH2O." Of course, Elkay meant 'easy H2O,' but I just took an epigenetics seminar where we learned about EZH2, a key enzyme in the Polycomb Repressive Complex 2 (PRC2). EZH2 is key in catalyzing and maintaining the [tri-methylation if lysine 27 in the tail of histone 3 (written "H3K27me3")] during mitosis (Hansen et al. 2008). At least I think that's how it works (if anyone knows better, please correct me if I'm wrong!).
So, real quick, your chromosomes are made up of DNA wrapped around histone proteins. This is essential because with some 3 billion base pairs of DNA, if it weren't packaged up nicely by histones it would be a HUGE MESS inside your cells. Anyway, these histones have 'tails' sticking out that can be modified in ways that basically allow genes to be turned on or off. This is significant because all of your DNA full of the Commands for Life is in every single one of your cells - yet not all genes are expressed. The addition of methyl-groups (methylation) to histone tails (as well as to DNA itself) is associated with gene silencing.
So when your DNA replicates during mitosis, EZH2 binds to H3K27, and slaps that tri-methyl mark to it, effectively telling the gene(s) in the region to 'shut up' so they don't get transcribed (Hansen et al. 2008). This way, your liver cells stay hepatic, your kidney cells renal, and your soul cells funky. It's apparently also critical in silencing HOXD and other during early development (Tsai et al. 2010). (Again, I'm not a molecular biologist so please someone correct me if I'm wrong!)
Hopefully these new water fountains aren't part of a bigger epigenetic experiment in which someone's subtly altering people's gene expression through malevolent manipulation of methyltransferase...
InformantsHansen, K., Bracken, A., Pasini, D., Dietrich, N., Gehani, S., Monrad, A., Rappsilber, J., Lerdrup, M., & Helin, K. (2008). A model for transmission of the H3K27me3 epigenetic mark Nature Cell Biology, 10 (12), 1484-1484 DOI: 10.1038/ncb1208-1484
Tsai MC, Manor O, Wan Y, Mosammaparast N, Wang JK, Lan F, Shi Y, Segal E, & Chang HY (2010). Long noncoding RNA as modular scaffold of histone modification complexes. Science (New York, N.Y.), 329 (5992), 689-93 PMID: 20616235... Read more »

Hansen, K., Bracken, A., Pasini, D., Dietrich, N., Gehani, S., Monrad, A., Rappsilber, J., Lerdrup, M., & Helin, K. (2008) A model for transmission of the H3K27me3 epigenetic mark. Nature Cell Biology, 10(12), 1484-1484. DOI: 10.1038/ncb1208-1484

Tsai MC, Manor O, Wan Y, Mosammaparast N, Wang JK, Lan F, Shi Y, Segal E, & Chang HY. (2010) Long noncoding RNA as modular scaffold of histone modification complexes. Science (New York, N.Y.), 329(5992), 689-93. PMID: 20616235

Biology

February 27, 2011
11:27 AM
560 views

Got beef with worms?

by zacharoo in Lawn Chair Anthropology

Photo: {http://news.brown.edu/pressreleases/2009/09/bilateral}, by Eric Rottinger at kahikai.orgFlipping through the current issue of Current Biology, it sounds like someone has some serious beef with acoelomorph flatworms. Apparently these critters have been used as a model for the 'missing link' between simple-bodied cnidarians (like jellyfish) and bilaterians (bilaterally symmetrical animals like you and me and flies and fish, and really a good deal of animal biodiversity); and this may be problematic according to the commentary. The origins of bilaterians is a major development in the evolution of body plans, a topic about which I know nothing. But I'm sold on the title and a line of the summary:Title: A Soap Opera of Unremarkable Worms.From the summary: "...acoelomorphs might instead be degenerate deuterostomes..."Take that, you shifty bastard flatworms.Acoelomorph roastLowe CJ, & Pani AM (2011). Animal Evolution: A Soap Opera of Unremarkable Worms. Current biology : CB, 21 (4) PMID: 21334293... Read more »

Lowe CJ, & Pani AM. (2011) Animal Evolution: A Soap Opera of Unremarkable Worms. Current biology : CB, 21(4). PMID: 21334293

Anthropology

February 11, 2011
01:37 AM
655 views

Why Lucy, what sweet kicks you had

by zacharoo in Lawn Chair Anthropology

For decades people have debated whether Australopithecus afarensis was an obligate biped like us, or whether our ancestor was a little less lithe in life on land. They asked, sort of, "Would Lucy have rocked some sweet Air Jordans, or would she have put some flat-foot orthotics in her new kicks?"
Carol Ward and colleagues report on a new fourth metatarsal of Australopithecus afarensis from Hadar in Ethiopia, over 3.2 million years old. The foot bone shows that A. afarensis had the two foot arches that we humans enjoy today.
Metatarsals are the longbones comprising much of the foot right before your silly-looking toes. One exceptional thing about our metatarsals compared to our ape cousins is that they contribute to two arches, one running front-to-back and another side-to-side. The arches provide critical support to our foot for bipedal stance, and a little Fred-Astaire-springiness as our foot hits the ground and then lifts off again when walking and running and sashaying.
The new A. afarensis metatarsal (AL 333-160, right) shows that by 3.2 million years ago, our ancestors had these arches, too. The twisting and angulation of the shaft relative to the base show these arches are similar to humans and our later fossil ancestors, whereas apes' MT4s tend to be less twisted and angled. Such morphology was hinted at by the famous Laetoli footprints from Tanzania, around 3.7 million years ago, also attributed to A. afarensis. Other evidence from the skeleton suggested Lucy was a biped and nothing else, and so this new find from Hadar further solidifies the idea that some of our skeletal adaptations to bipedalism are ancient indeed. AL 333-160 image: Carol Ward and Kimberly Congdon (http://news.sciencemag.org/sciencenow/2011/02/lucy-had-a-spring-in-her-step.html?ref=hp)The PaperWard, C., Kimbel, W., & Johanson, D. (2011). Complete Fourth Metatarsal and Arches in the Foot of Australopithecus afarensis Science, 331 (6018), 750-753 DOI: 10.1126/science.1201463... Read more »

Ward, C., Kimbel, W., & Johanson, D. (2011) Complete Fourth Metatarsal and Arches in the Foot of Australopithecus afarensis. Science, 331(6018), 750-753. DOI: 10.1126/science.1201463

January 27, 2011
11:05 PM
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A species by any other name...would leave us with the same problem

by zacharoo in Lawn Chair Anthropology

This is a great big week for anthropology coverage. The sequencing of the orangutan (Pongo species) genome made the cover of Nature. It's grant-writing-dissertation-formulating-prelim-studying time for me so I haven't had a chance to read this one yet. Science has a couple paleoanthropology-related stories, including two by Ann Gibbons. The first is about recent research on ancient DNA, and how this informs the debate about 'modern human' origins. But there's also a short blurb on what the eff "species" means.
This is a great effing question! The textbook species definition is that proffered by Ernst Mayr: populations of actually or potentially interbreeding individuals, capable of producing viable (and fertile) offspring. Cool, so a dog and a cat are different species because if they mated (ew) no ungodly animal would come from this monstrous union. Expensive high-tech multivariate Scientific reconstruction simulations show the abomination would probably look like this:
But there are many "good" plant and animal species that do mate and reproduce successfully ('hybridize'). Very often these hybrids are sterile, but then very often they're not. This has led researchers to come up with scores of other ways to define species (Holliday (2003) has a great discussion on the matter).
Worse, there's no way to measure, genetically or morphologically, just how different things should be before they can be called different species. The late Morris Goodman and others (Wildman et al. 2003) argued that humans and chimpanzees are so genetically similar that chimps, now in the genus Pan, should be moved to our genus Homo to denote how similar we are. But any other, non-genetic comparison would put our chimp cousins in a very different group from us. Moreover, the effects of hybridization seem, to me at least, to be fairly unpredictable, at least superficially. That is, the outcome of hybridization is highly contingent on what animals are hybridizing, and on these lineages' own evolutionary histories (this is the intractable problem that made me abandon doing hybrid work for my dissertation. Some day though...).
A major issue relates to what I blogged about yesterday: both 'species' and 'hybrid' are terms we've found ourselves with, but they have no inherent meaning in themselves, other than whatever we give them. So it's funny to read this from Gibbons' story:In the real world, [Jean-Jacques Hublin] says, Mayr's concept doesn't hold up: "There are about 330 closely related species of mammals that interbreed, and at least a third of them can produce fertile hybrids."But is it Mayr's species concept that's flawed, or was it misguided to have put these hybridizers into different species in the first place? Should we delineate species based on our a priori conception about whether two things are different, or should a definition of 'species' determine what we call them? Or does it even matter?
To this end, Gibbons's other story describes the morphologically-unremarkable Denisova fossils as belonging to "a new type of human." Well, now what the eff does that mean? We're back to "The Species Problem" (the title of Gibbons's article), but with a new term. And pretend for a moment that the Denisovan fossils didn't yield DNA: the pinky and tooth probably would not have made headlines. Pretend they did have diagnostic cranial remains - would we have recognized them as being so distinct as their genes indicate?
For that matter, I wonder how many arguably 'modern' human fossils would still retain the modern moniker if we could analyze their genes...
ReferencesGibbons, A. (2011). The Species Problem Science, 331 (6016), 394-394 DOI: 10.1126/science.331.6016.394
Gibbons, A. (2011). A New View Of the Birth of Homo sapiens Science, 331 (6016), 392-394 DOI: 10.1126/science.331.6016.392
Holliday, T. (2003). Species Concepts, Reticulation, and Human Evolution Current Anthropology, 44 (5), 653-673 DOI: 10.1086/377663
Wildman, D. (2003). Implications of natural selection in shaping 99.4% nonsynonymous DNA identity between humans and chimpanzees: Enlarging genus Homo Proceedings of the National Academy of Sciences, 100 (12), 7181-7188 DOI: 10.1073/pnas.1232172100... Read more »

Gibbons, A. (2011) The Species Problem. Science, 331(6016), 394-394. DOI: 10.1126/science.331.6016.394

Gibbons, A. (2011) A New View Of the Birth of Homo sapiens. Science, 331(6016), 392-394. DOI: 10.1126/science.331.6016.392

Holliday, T. (2003) Species Concepts, Reticulation, and Human Evolution. Current Anthropology, 44(5), 653-673. DOI: 10.1086/377663

Wildman, D. (2003) Implications of natural selection in shaping 99.4% nonsynonymous DNA identity between humans and chimpanzees: Enlarging genus Homo. Proceedings of the National Academy of Sciences, 100(12), 7181-7188. DOI: 10.1073/pnas.1232172100

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