Why Lucy, what sweet kicks you had

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.
UPDATE: Thinking about this finding in the shower this morning, I recalled that buddies Jerry DeSilva and Zach Throckmorton recently published a study where they concluded, based on the morphology of the end of the tibia, that A. afarensis probably had at least a rear-foot arch. Interestingly, though, they found some hominid specimens probably had “asymptomatic flatfoot.” Lucy (AL 288) was among these, so maybe she’d be sporting orthoticized Jordans after all.
The Papers
DeSilva JM, & Throckmorton ZJ (2010). Lucy’s flat feet: the relationship between the ankle and rearfoot arching in early hominins. PloS one, 5 (12) PMID: 21203433

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

Australopithecus africanus (?) foot bone, and a small rant

Be forewarned, this summary of a recent article on an A. africanus fifth metatarsal also features a short rant. So feel free to stop reading after I start to sound preachy or crazy.

Friend and colleague Jerry DeSilva is part of a recent study of the fossil Stw 114/115, the earliest and most complete hominin fifth metatarsal (the bone forming the side “wall” of your foot just before your little toe). Probably it can be attributed to Australopithecus africanus. Lead author is Bernhard Zipfel of the University of the Witswatersrand. On an aside, Bernhard is the curator of the fossil collections at Wits, so if you’re interested in researching their collection, he’s the one to contact. I met him a few weeks ago, and he is very nice and friendly.

Back to the paper, the authors present a thorough description of the fossil foot bone, a thorough comparison of it to human and great ape homologues, and an exploratory multivariate analysis. The conclusion is that the fossil is decidedly human-like, indicating that the individual who possessed this foot (presumably A. africanus) had a lateral foot functionally identical to modern humans (read “obligate biped”). The authors infer from its overall form that feet of A. africanus (or, again, whatever species this fossil belonged to) had both a longitudinal and a transverse arch, just like humans (non-human primate feet only have the transverse arch).

I have to say, this is an excellent paper, especially compared to lots of studies I’ve read over the past few years. The qualitative description and comparison of the fossil points to many differences between human and ape fifth metatarsals, and similarities between the fossil and humans. Observations made with the eye are then corroborated and elaborated with a quantitative analysis. In contrast, many (but of course not all) studies today largely omit qualitative descriptions and comparisons, delving straight into quantitative analyses. I think this is in attempt to be “scientific” and objective. This zeal for being ‘scientific’ with regard to quantitative methods stands in curious opposition to a general lack of actual hypothesis testing in much of the literature. Of course, this is not a jab at exploratory and descriptive studies, which by their nature usually don’t have hypotheses to test.

I think it’s important to remember that not all questions can (or have to) be addressed by strictly quantitative studies (i.e. by numbers). For example, human metatarsals have a groove separating the head from the shaft—this feature relates to our increased ability to “dorsiflex” our toes when we walk (think of how your toes are oriented relative to the rest of your foot when on tip-toes). This groove is absent in apes. How can a quantitative analysis of human vs. ape metatarsals account for this? I suppose it could be scored as ‘present’ or ‘absent,’ or scored by the relative expression of the groove (i.e.0=absent, 1=weak, 2=deep, etc.). But, the former, dichotomizing scoring system fails to account for variation, while the latter can become quite subjective. On the other hand, I suppose a very complex geometric morphometric analysis could use an immense amount of landmarks to describe the shape of the metatarsal, including the groove (or lack thereof) behind the head. But then you get into the issue of comparing biologically non-homologous structures (although Bookstein and others have done a good—or rather ingenious—job developing methods for making ‘geometrically homologous’ semi-landmarks, and Klingenberg has recently described a way to compare features that are variably present or absent). The main point here is that by focusing/relying solely on ‘the numbers’ (or ‘the science’), researchers stand to miss some important anatomical information.

Sorry about the rant. Anyway, the paper doesn’t really miss anything. It’s a great example of the union of qualitative and quantitative analyses. My only comment is on their human reference sample of “Victorian British” people. I don’t know the sample, but they probably wore shoes. A more apt comparison might have been with humans that didn’t wear shoes, since shoes really affect our foot anatomy. Of course if this sample was habitually unshod, then this doesn’t really matter. And regardless, the Sts 114/115 Australopithecus africanus (?) fifth metatarsal shows great similarity to those of humans, and probably functioned like those of humans.


Zipfel B, DeSilva J and Kidd R. Earliest complete hominin fifth metatarsal—Implications for the evolution of the lateral column of the foot. American Journal of Physical Anthropology, in press. DOI 10.1002/ajpa.21103