Talk at UW Madison tomorrow

I’ve just flown some 7,000 miles for a 2-week stint in the USA. I’m first spending a week in Madison, WI as part of the faculty exchange between Nazarbayev University and the Unversity of Wisconsin Madison. Next week I will be in St. Louis for the AAPA conference, catching up with colleagues and presenting an analysis of brain growth in chimpanzees. Highlight of the trip so far: potable tap water (I can’t stress enough the importance of staying hydrated).

Image from Wolfram Alpha.

Image from Wolfram Alpha. Actual route is through Frankfurt, Germany.

Tomorrow I will be giving a talk here at UWM about wrangling important information out of a secretive fossil record. If you’re in the area, please come check it out! Here’s a flier with more info:


Shockingly alarming pedagogical discovery

You heard it here first: class attendance is correlated with test performance. The discovery was made in two undergraduate anthropology courses in Astana, Kazakhstan, though the findings can probably be replicated elsewhere. This result runs counter to the widely held consensus among undergraduate students, that it is not important to attend lectures.

Midterm exam scores (out of 32 points) plotted against class attendance (left) and participation grades (right). Participation is based on in-class quizzes over readings, and so measures students exposure to both lecture and reading.

Figure 1. Midterm exam scores (out of 32 points) plotted against class attendance (left) and participation grades (right), for one biological anthropology class. Correlations and regressions slopes are significantly higher than zero.

Highly paid scientists collected data on students’ midterm exam scores, the number of sessions students were physically present at a lecture (“attendance”), and how they performed on in-class quizzes (“participation”). As quizzes are based on course readings, participation measures active investment beyond simply attendance.

Figure 2. Same variables plotted as in the previous figure, but for a second class.

Figure 2. Same variables plotted as in the previous figure, but for a second class (exam out of 25 points). In addition to linear regression lines (solid black), polynomial regressions (dashed red) were also fit for this class. Polynomial regressions have slightly lower standard errors and slightly higher coefficients of determination. Linear regressions have slopes significantly different from zero while polynomial coefficients are not statistically significant. Either way, more investment generally translate into higher grades.

The researchers were shocked to find positive relationships between students’ exam performance and measures of course participation and active participation. “With the rise of unsourced information on the internet, we assumed students didn’t need to go to class – what could a professor possibly say in lecture that can’t hasn’t already been said on ‘the Net’,” said an out of touch analyst who wasn’t involved in the analysis. The lead investigator of the study remarked, “All college students are hard-working and motivated, so we figured they would read and come to lectures if they knew they’d benefit. Our findings hint that maybe they don’t know everything after all.”

Scientists think these findings have important implications for students everywhere. An empirical link between active participation in class and grades mean that a student’s chances of doing passing or even excelling in a class can improve dramatically with increased attendance. So take note, students: read and go to class! Who knows, you might even learn something from it.

* These are my students’ actual grades and attendance this semester. No undergraduates were harmed in this study.

A neonatal perspective on Homo erectus brain growth

The Mojokerto infant Homo erectus. The fossil as preserved is on the left, and on the right is the reconstructed brain based of CT scans of the fossil (Figure x from Balzeau et al., 2005). The fossil and endocast are viewed from the right side so the front of the fossil is to the right.

The Homo erectus infant from Mojokerto. The fossil as preserved is on the left, and on the right is the brain cast reconstructed from CT scans of the fossil (Figure 7 from Balzeau et al., 2005). The fossil and endocast are viewed from the right side so the front is on the right and back is on the left.

My paper (coauthored with Jeremy DeSilva) about brain growth in Homo erectus will be coming out soon in Journal of Human Evolution. I’ve been working on this study for a while now, so it feels good to’ve turned in the approved copy edits at long last. I’ve discussed this work a bit while it was in progress (here, here, and here), and the final version is a little different from what I posted back then, but I won’t rehash everything here. The take home message is that by around 1 million years ago, Homo erectus from Java probably had brain growth rates during early infancy in the modern human range. Really rapid early brain size growth is a unique feature of humans, and our analysis shows this trait, and many other correlates of it, were likely present early in our evolutionary history.

Our results are based on a custom resampling test, the codes for which I’ve posted here on my R Codes page. Now you can do this kind of analysis yourself!

Until the paper actually comes out, here’s the abstract:

The Mojokerto calvaria has been central to assessment of brain growth in Homo erectus, but different analytical approaches and uncertainty in the specimen’s age at death have hindered consensus on the nature of H. erectus brain growth. We simulate average annual rates (AR) of absolute endocranial volume (ECV) growth and proportional size change (PSC) in H. erectus, utilizing estimates of H. erectus neonatal ECV and a range of ages for Mojokerto. These values are compared with resampled ARs and PSCs from ontogenetic series of humans, chimpanzees, and gorillas from birth to six years. Results are consistent with other studies of ECV growth in extant taxa. There is extensive overlap in PSC between all living species through the first postnatal year, with continued but lesser overlap between humans and chimpanzees to age six. Human ARs are elevated above those of apes, although there is modest overlap up to 0.50 years. Ape ARs overlap throughout the sequence, with gorillas slightly elevated over chimpanzees up to 0.50 years. Simulated H. erectus PSCs can be found in all living species by 0.50 years, and the median falls below the human and chimpanzee ranges after 2.5 years. Homo erectus ARs are elevated above those of all extant taxa prior to 0.50 years, and after two years they fall out of the human range but are still above ape ranges. A review of evidence for the age at death of Mojokerto supports an estimate of around one year, indicating absolute brain growth rates in the lower half of the human range. These results point to secondary altriciality in H. erectus, implying that key human adaptations for increasing the energy budget of females may have been established by at least 1 Ma.

eFfing #FossilFriday: toolmakers without tools?

Matt Skinner and colleagues report in today’s Science an analysis of trabecular bone structure in the hand bones of humans, fossil hominins and living apes. Trabecular bone, the sponge-like network of bony lattices on the insides of many of your bones, adapts during life to better withstand the directions and amounts of force it experiences. This is a pretty great property of the skeleton: bone is organized in a way that helps withstand usual forces, and the spongy organization of trabeculae also keeps bones fairly lightweight. Win-win.

An X-ray of my foot. Note that most of the individual foot bones are filled with tiny 'spicules' (=trabeculae) of bone. Very often they have a very directed, or non-random, orientation, such as in the heel.

An X-ray of my foot. The individual foot bones are filled with narrow spicules (=trabeculae) of bone. Very often they have a directed, or non-random, orientation: in the calcaneus, for instance, they are oriented mostly from the heel to the ankle joint.

This adaptive nature of trabecular bone also means that we can learn a lot about how animals lived in the past when all they’ve left behind are scattered fossils. In the present case, Skinner and colleagues tested whether tool use leaves a ‘trabecular signature’ in hand bones, looking then for whether fossil hominins fit this signature. Their study design is beautifully simple but profoundly insightful: First, they compared humans and apes to see if the internal structure of their hand bones can be distinguished. Second, they tested whether these differences accord with theoretical predictions based on how these animals use their hands (humans manipulate objects, apes use hands for walking and climbing). Third, they determined whether fossil hand bones look more like either group.

Comparison of first metacarpals (the thumb bone in your palm) between a chimpanzee (left), three australopithecines, and a human (right). In each, the palm side is to the left and the wrist end of the bone (proximal) is down. Image by Tracy Kivell, and found here.

Looking at the image above, it’s difficult to spot trabecular differences between the specimens with the naked eye. But computer software can easily measure the density and distribution of trabecular bone from CT scans. With these tools, researchers found key differences between humans and apes consistent with the different ways they use their hands. Neandertals (humans in the past 100 thousand years or so) showed the human pattern, not unexpected since their bones look like ours and they used their hands to make tools and manipulate objects like we do.

What’s more interesting, though, is that the australopithecines, dating to between 1.8-3.0 million years ago, also show the human pattern. This is an important finding since the external anatomy of Australopithecus hand bones shows a mixture of human- and ape-like features, with unclear implications for how they used their hands. Their trabecular architecture, reflecting the forces their hands experienced in life, is consistent with tool use.

This is a very significant finding. Australopithecus africanus fossils from Sterkfontein aren’t associated with any stone tools; bone tools are known from Swartkrans, though it is unclear whether Australopithecus robustus or Early Homo from the site made/used these. In addition, in 2010 McPherron and colleagues reported on a possibly cut-marked animal bone from the 3.4 million year old site of Dikika in Ethiopia, where Australopithecus afarensis fossils but no tools are found. Skinner and colleagues’ results show that at the very least, South African Australopithecus species were using their hands like tool-makers and -users do.

This raises many fascinating questions – were australopithecines using stone tools, but we haven’t found them? Were they using tools made of other materials? What do the insides of Australopithecus afarensis metacarpals look like? What I like about this study is that it presents both compelling results, and raises further (testable) questions about both the nature of the earliest tools and our ability to detect their use from fossils.

Another small Middle Pleistocene person

Last year I brought up the implications of the small female pelvis from Gona, Ethiopia for body size variation in Homo erectus (see previous post). This individual was much smaller than other Middle Pleistocene Homo fossils, indicating size variation comparable to highly sexually dimorphic gorillas and unlike recent human populations. Before this pelvis, most known Homo erectus fossils were fairly large (comparable to living people), with only a few hints of much smaller individuals (e.g., KNM-ER 427000, KNM-OL 45500). Now joining this petite party, this tiny troop, this little lot, this compact cadre, etc., is KNM-WT 51261, a 750,000 year old molar from Kenya (Maddux et al., in press).

Occlusal area for hominin first molars. The tooth is from Fig. 2 and the plot from Fig. 3 in the paper.

Occlusal area for first molars in the genus Homo. The tooth image is from Fig. 2 and the plot from Fig. 3 in Maddux et al. Lookit how tiny it is!

This ‘new’ specimen substantially increases the range of size variation among early African H. erectus molars, although the expanded range isn’t remarkable compared with later Homo samples such as from Zhoukoudian cave in China or Neandertals. What is different, though, is that most of the highly variable samples show a fairly continuous range of variation, while the WT 51261 molar is a considerable outlier from the rest of the African Middle Pleistocene sample (a lot like the situation with the Gona pelvis). So this tooth re-raises an important question: were smaller specimens like Gona and WT 51261 as rare in life as they are in the fossil record, or was such great size variation common in the Middle Pleistocene? How we reconstruct what kind of animal Homo erectus was differs depending on the answer to this question.

Driving nails into the 2014 Lawn Chair

It’s that time again, when we come to bury the year we’ve just defeated, only to celebrate the zombie birth of a new onslaught of days to clobber. In the spirit of auld lang syne, let’s recap the highlights of Lawn Chair in 2014.Georgia dinos 2014

Osteology was everywhere: although I am wont to see bones everywhere in everyday life, this year I only wrote about it four times. First there were the baby bones in cafe upholstery in my hometown of Kansas City, then the giant sheep bones in my new home of Astana. I discovered that animal bones littered the landscape of desert Mangystau, and then I spotted a vertebra hiding in a helmet at a conference in Italy. I also tweeted about a false femur head from a karaoke bar in Astana. You can’t escape. 2015 is sure to be more osseous.BONES!
eFfing Fossil Friday reboot: This old series focusing on fossils furtively restarted on a plane, when I uncovered the conspiracy that the Australopithecus africanus cranium Sts 71 was actually the Kryptonian codex. I later wrote about the Sima de los Huesos skulls, Neandertal poop, the origins of feathers on badass dinosaurs, the 45,000 year old Ust’-Ishim femur and its delicious DNA, and facial flanges in early mammals and nearly modern baboons. Fossils are the best, and 2015 is bound to be as fossiliferous as last year.Ancient DNA was boss: In addition to the earliest ‘modern’ human DNA from Ust’-Ishim, 2014 also witnessed a swath of studies early on attesting to the success of paleogenomics. We also got a first glimpse into epigenetics of ancient humans, and the potential importance this will have in uncovering how our DNA makes us human. Along these lines, for 2015, I’d be keen to see more work on miRNA and other aspects of gene regulation in ancient genomes.

Screen Shot 2014-10-24 at 11.26.31 AMR codes: I’ve posted R code for the analysis from my paper that came out this year, comparing mandibular growth in humans and Australopithecus robustus (I didn’t get to talk about that paper when it came out because I was in the middle of the Rising Star Workshop. Things to look forward to in 2015…). I’ll also be posting code for the analysis of brain growth in Homo erectus once that paper is published, and I have already posted code for creating the pretty pictures from the paper.

Brain size data (left) and the average annual rates from birth calculated from pairs of specimens (right). Black=humans, green=chimpanzees, red=gorillas, blue=Homo erectus.
Body size variation in Homo erectus: A response to a response to a paper led me to reexamine sexual dimorphism in body size in our early ancestor – seems it was higher than has lately been appreciated, and there are many potential reasons for this. I presented the initial results of this investigation on the blog and at a conference, and am now writing this up for publication. This investigation is based on resampling statistics, nothing as new and flashy as in the growth studies. I will post code for these analyses on the R Codes page in due time.

Dimorphism ratios copy

Resampled ratios of dimorphism, calculated by dividing the average of six randomly selected male body masses by a randomly selected female mass. The blue star in each plot is the empirical ratio of average male mass/average female mass. For all species the average resampled ratio is almost identical to this empirical value. The red line marks the ratio of the six largest (male?) Homo erectus mass estimates divided by the estimated mass of the Gona (female?) pelvis. The Homo erectus male/female difference is rarely observed in chimps and humans, but is common in gorillas. Gorillas display high levels of sexual dimorphism, suggesting this may have been the case for Homo erectus as well.

Classroom lab activities: This year I added a lab components to my courses here at NU, and I posted up two of the lab activities I did in my classes this semester. Last spring, I got the idea for an activity in which students measure toe joint angles on digital images, to test whether Ardipithecus kadabba and other hominin toes can be distinguished from apes’. This semester, students in my human evo-devo class did this study, and generally found hominin toes to be more angled than apes’. Hypothesis tested. My Intro to Bio Anthro class tested whether their limb proportions fit expectations based on Allen’s Rule, and mystery ensued. My classes next term aren’t as conducive to lab activities, but if I come up with any good assignments I’ll be sure to post them.class models both copy

Now that 2014 is laid to rest, here’s to a bright and successful zombied 2015! Жаңа Жылыңызбен!

eFfing Fossil Friday: Funky facial flanges #FFF

David Krause and colleagues announced in this week’s Nature the discovery of a new species of extinct mammal, Vintana sertichi, that lived in what is now Madagascar between 66-72 million years ago. The species is based on a very well-preserved cranium of an early gondwanatherian (if you want to impress your friends this weekend, gratuitously use the word “gondwanatherian”). I don’t know much about early mammals like this, but it sounds like it was a weird creature (see the Stony Brook press release). Just looking at it’s face there’s something that sticks out as strange:

Ventana sertichi cranium (Reich et al. 2014, Figure 1a). Left is a 3D CT reconstruction, right is a line drawing highlighting all the individual bones (so many cranial bones). The view is from the right side, so the nose is on the right, the eye is the big hollow in the middle, and the back of the skull is on the left. The jugal flanges are the downward projections.

Vintana sertichi cranium (Reich et al. 2014, Figure 1a). On the left is a 3D CT reconstruction, and on the right is a line drawing highlighting all the individual bones (so many cranial bones). The view is from the right side, so the nose is to the right, the eye socket is the shadowy hollow in the middle, and the back of the skull is on the left. The jugal flanges are the downward projections.

Jutting downward from the sides of the jaw are ‘jugal flanges,’ projections of bone on the homologs of human cheeks. Projections of like these usually serve as muscle attachment sites, and the size of the projection generally reflects the size of the muscle. These facial flanges anchor the masseter muscle, a major chewing muscle that helps close the jaw. The size of this flange in Vintana suggests its chomp packed a punch. A debilitating bite. A face not even a mother could love (so now they’re extinct).

Vintana‘s bony tear-catchers caught my eye because most primates I’ve seen have, you know, less heinous faces. Scouring the internet, big jugal flanges are a fairly rare sight, but can apparently be found in glyptodonts (giant, armadillo-like mammals that lived tens of thousands of years ago) and various sloths. The closest thing I’ve seen to this gross bony flange in Primates are on the zygomatic bones of some extinct, baboon-like animals, such as Dinopithecus ingens:

Fragmentary skull, viewed from the top, of Papio (a.k.a. Dinopithecus) ingens, from Swartkrans, South Africa. Photo credit: CalPhotos.

Fragmentary skull, viewed from the top, of Papio (a.k.a. Dinopithecus) ingens, from Swartkrans, South Africa. As a punishment for its zygomatic excess, its face was confiscated. Photo credit: CalPhotos.

and Theropithecus brumpti

Theropithecus brumpti from the Omo basin. Photo credit: CalPhotos.

Theropithecus brumpti from the Omo Basin, Ethiopia. Photo credit: CalPhotos.

So some primates dabbled in jugal flangery like Vintana, but Natural Selection was having none of it. Anyway, Vintana overcame this craniofacial adversity with characteristic Mesozoic moxie, and is an important piece in the puzzle of mammal evolution. It will be interesting to see what other mammalian surprises the Mesozoic has in store for paleontologists.

My ESHE poster is Gona blow your mind

I’m in Italy for the annual meeting of the European Society for the Study of Human Evolution. It’s been a great conference, seeing interesting talks (check out #eshe2014 on Twitter), meeting old friends and meeting new ones, and enjoying excellent food and espresso. Here’s the poster I presented yesterday (download pdf):Screen Shot 2014-09-20 at 9.33.38 AM

It’s a follow-up to posts here and here. The long and short of it is, there was a substantial amount of body size variation (i.e., between males and females) in Homo erectus, on par with levels seen in modern day gorillas. This is interesting because H. erectus brain size (and brain size growth) would have required massive amounts of energy, so some have hypothesized a cooperative breeding strategy; sexually dimorphic species generally do not engage in such cooperative behavior. So I suggest that body size variation in H. erectus is an ecological strategy, with small female body size reducing the metabolic burden on mothers.

Osteology Everywhere: Literally

Last weekend, Kazakhstan celebrated Constitution Day. Rather than stick around for the festivities in the florid Capital city, some friends and I ventured out West to Mangystau, to the deserts flanking the Caspian Sea. Although much of the area is sprawling, barren desert, it’s geologically much more interesting than my home here in the White Tomb.

2014-08-30 17.31.29

A perfect camping spot here on Mars.

The purpose of the trip was ostensibly holiday, but in landscapes such as this my field training kicks in. While I made sure to take in the scenic views, my gaze was mostly directed downward, as on survey, in search for bones, lithics and other signs of paleontological promise.

One thing about Life is that it teems. I don’t mean the obvious, ubiquitous microbes or infinitesimal infestations on all our faces. Even the big stuff can thrive, even in seemingly inhospitable places.

This little buddy wants nothing to do with everything.

This curmudgeon puts the ‘turd’ in ‘turtle.’

Some buddies on their way to work.

These buddies are on their way to an important meeting at the office.

But what goes up must come down, the only promise is The End. As a result of this shared fate, many of the landscapes we encountered were literally littered with the bony remnants previous denizens. Sun-scorched and bleached, the calling cards of Tetrapods stuck out like sore thumbs among the dirt and scrub.

Hip off the old block.

Hip off the old block.

A horse doing its best impression of SK 46.

A horse doing a good impression of SK 46.

Mangystau boasts an embarrassment of turtle bones and shells.

Mangystau boasts an embarrassment of turtle bones and shells.

A small, noble beast.

Alas, this was a noble little buddy.

I will admit I have no idea what animal this comes from, but I would guess some small mammal. If you know, please tell!

I will admit I have no idea what animal this comes from, but I would guess some small mammal. If you know, please tell me.

But this surface smorgasbord of bones will not translate into a future fossil festival. Sitting on the surface, bones like these are likely to be scattered, trampled, disturbed by anthropology nerds. Most will not get the chance to sink into the Earth, soak up leaching minerals, and lie in wait for paleontologists of the future. In desert landscapes such as in Mangystau, ‘osteology everywhere’ is an ephemeral description.

eFfing Fossil Friday: Feathers & Ink

I’ve been traveling here and there lately, so I’ve missed a fortnight’s FFFs. So to atone, this post is a threefer.

Last week I was visiting my family in Kansas City, and was debating whether to get a badass dinosaur tattoo. Right on cue, the cover of last week’s Nature featured this feathery friend (right): the 11th Archaeopteryx skeleton. From the previous 10 skeletons, we know that this 150 million year old dinosaur had feathers on its upper limbs and tail. But this new specimen from China, described by Foth and colleagues, also has plush pennaceous plumage bedazzling its neck, lower legs and feet. So decked in down, this new fossil suggests that Archaeopteryx and other dinos originally evolved feathers for some function besides flight, such as social displays (some living birds have taken this to ridiculous extremes). Later species of winged theropods (i.e., birds) eventually adapted feathers for flying (the concept of exaptation).

Also, this closeup, under ultraviolet light, of the specimen’s wing (impressions) and phalanges shows how badass and clawed birds used to be. They just don’t make them like they used to.

Extended Data Fig. 4a-b from Foth et al., 2014.

Taking this Nature cover as a sign, I went ahead and got a different fossil permanently etched somewhere on my person:

Fig. 1a from Rauhut et al., 2012.

This, as described in the title of the 2012 paper, is an “exceptionally preserved juvenile” of the dinosaur species Sciurumimus albersdoerferi. This little buddy is one of the most complete dinosaur skeletons in existence, and even preserves some skin and “protofeathers” (not as full and feathery as in the Archaeopteryx described above). And that little bar beneath the lower jaw is the hyoid bone. THEY HAVE ITS HYOID! If only more hominin fossil juveniles were so well preserved (and badass).

Finally, although CNN is usually insufferable, Thursday they reported that more than 18 dinosaur skeletons that had been smuggled out of Mongolia and into the U.S. have been returned to where they belong. The coverage doesn’t really get into it, but for me this highlights a major paleontological problem – private collectors (and often a black market) make scientifically important fossils unavailable to researchers (many of the Mongolian fossils were very complete skeletons). Fossils are the only direct evidence of life in the past (would you ever believe that this was a real animal if there wasn’t physical evidence?), so the theft and private trade of such important evidence is problematic. This hit home in paleoanthropology with the announcement of Darwinius masillae five years ago (the fossil was purchased for scientific study for a large sum of money). I don’t know what the Mongolian government will do with their returned fossils, but their repatriation is probably good for paleontologists.