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Sunday, September 25, 2011

Pictures worth thousands of words and dollars

ResearchBlogging.orgLooking 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.

References
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

Teaching next summer

When I was working at Dmanisi this summer, I used a lot of my free time to develop a course on human evolutionary developmental biology, or evo-devo. I submitted this to my department, and I'm excited to announce that I'll be teaching this class at U of M in Spring 2012. So if you're at UM and want to take a badass class exploring the evolution and development of the human body, keep an eye out for this new anthropology offering (NB I need to come up with a catchy title for the class still).

The tentative textbook for the class will be Lewis Held's Quirks of Human Anatomy: An Evo-Devo Look at the Human Body, which I just got in the mail yesterday. It got very good reviews and should be an interesting read, and with just under 3000 references it has a pretty useful bibliography, too. I'm really looking forward to reading this, and even the first page of the preface points to something promising:
"In Chapter 13 of Origin, Darwin asserted that the evidence from embryology alone was strong enough to convince him of the principle of common descent. Human embryos make many structures we don't need, and we destroy others after we've gone to the trouble of making them. No engineer in his right mind would ever allow such idiocy."
I can't wait to read about these idiocies.

Teaching is an important part of my work, but I'll admit that sometimes I'd rather be doing other things than preparing lessons, assignments and such. I have to say, though, I've had a lot of fun preparing this class so far. I'll keep you posted about what I think of the book and how the course-planning comes along.


Sunday, September 18, 2011

[insert clever quip about australopithecus hips]

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.

ResearchBlogging.org

Lots of interesting questions arise from these fascinating new fossils. "The more you know," right?

References
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

Monday, September 12, 2011

Tess Tossed Tyrone

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.

ResearchBlogging.org
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.

Reference
Gettler 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.1105403108

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

Photo credit: google (image) "Bill Cosby Fatherhood"

Thursday, September 8, 2011

New Australopithecus sediba analyses

A slew of papers analyzing the brain, hands, feet, and pelvis of Australopithecus sediba were just published in the journal Science. I have not had a chance to read them yet - nor will I for a few days as I'm in a wedding Saturday [not mine :( ] and the partying starts in a few hours. So I'm afraid I won't be able to report on and interpret these on the blog for a while. Please stay tuned!
CT reconstruction, from Science (follow link above).

The exact same thing happened to me 2 years ago when the Ardipithecus ramidus skeleton was (finally) published. I remember waiting in the Detroit airport to board a flight to St. Louis to begin my platonic soul-mate's bachelor party, and I get a flurry of emails on my phone announcing the skeleton in the 15 year old closet.

So media beware - whenever I'm in a wedding, badass new fossil studies will be published.