I'm tired of cutesy foot-related titles

I don’t have a lot to say about the new footprints from Ileret, described by Matthew Bennett and colleagues. Seems like a nicely done study, particularly given the length constraints in Science.

With respect to the comparison with Laetoli, I think that the perspective article by Robin Crompton and Todd Pataky sort of hits the important questions:

Were the Ileret footprint makers' feet the first to function just like ours? Do the Laetoli prints represent more "apelike" foot function? Do all regions of a footprint record local maxima in foot pressure, or do some record how pressure changes over time, as braking forces change to propulsive ones? None of these questions can be answered at present. It is not even clear whether a nondivergent big toe is important for the extended push-off typical of human walking or just a by-product of other anatomical changes (1, 2, 4, 8). The effect of substrate recoil or of later abrasion on the reliability of footprint measurements must also be established (6-8). But the findings of Bennett et al. herald an exciting time for studies of the evolution of human gait.

Merely quantifying significant differences in the prints doesn’t really tell us much about australopithecine gait or foot function. My impression of footprints (har!) is that it’s tough to analyze them.

There’s much about adduction of the big toes in the press and the abstract of the paper. The text description doesn’t quite support the interpretation that Ileret is identical to recent human footprints, though:

The angle of hallux abduction, relative to the long axis of the foot, is typically 14 compared to, and statistically distinct from (table S4), 8 for the modern reference prints and 27 for the Laetoli prints (Fig. 4A).

They’re closer to Holocene people than to Laetoli, since the range of living prints overlaps with these. The statistics are trickier than they might look, since these are multiple trails, but each consisting of the prints of a single individual. So I’m skeptical that they really are statistically different from humans in their big toes.

But anyway, they’re in-between Laetoli and humans, so that makes a good evolutionary sequence!

I’m a bit skeptical of the body size estimation in the paper. Not the regression – that’s pretty straightforward. More the interpretation that the foot size is necessarily “Homo erectus/ergaster”, or that they’re a “perfect fit” for the Nariokotome skeleton.

The average foot length recorded for the FwJj14E trail is 258 mm. Two hundred fifty eight millimeters is not a very big foot – it’s a shade bigger than a U.S. men’s size 8. You can have a tall person with a size eight shoe, to be sure. But their height estimate of 1.75 m is not all that tall – it’s 5 foot 8 inches, which is around the 25th percentile for height for American men (and around the 90th percentile for American women).

Now, the question here is whether that’s sufficient to make them “Homo erectus/ergaster” prints, or whether they might be A. boisei. That depends on whether Australopithecus had big feet. It doesn’t seem to unlikely that a male A. boisei might be 1.4–1.5 m in height, and if they had relatively big feet, well then Katy bar the door!

I don’t have any strong feelings – at 1.5 million years old, these prints might be too recent to be A. boisei anyway. But it seems to me there is this question about body size estimation, when you don’t have any evidence about the body proportions.

References:

Bennett MR, Harris JWK, Richmond BG, Braun DR, Mbua E, Kiura P, Olago D, Kibunjia M, Omuombo C, Behrensmeyer AK, Huddart D, Gonzalez S. 2009. Early hominin foot morphology based on 1.5-million-year-old footprints from Ileret, Kenya. Science 323:1197-1201. doi:10.1126/science.1168132

Crompton RH, Pataky TC. 2009. Stepping out. Science 323:1174-1175. doi:10.1126/science.1170916