Footprints through time

A recent paper (Bennett et al. 2009) announced the discovery of 1.5 million year old fossilized footprints from Ileret, Kenya, almost certainly belonging to Homo erectus (see also this commentary article by Ann Gibbons). Homo erectus was already known from fossils such as the Turkana Boy to be very similar to modern humans below the neck, and completely adapted to bipedal locomotion. So it was no suprise when the footprint analysis showed that the owners of the Ileret footprints had a fully modern foot shape and were pushing off their big toes and shifting their weight exactly as modern humans do.

Answers in Genesis, of course, was delighted to report on this, claiming that it confirmed their belief that Homo erectus was a modern human (never mind the more primitive features of pelvis, shoulder and skull found in Homo erectus). So did the Institute for Creation Research. But AIG and ICR carefully avoided mentioning information from the paper that did not fit with their agenda.

There is another famous set of fossilized hominid footprints, the 3.7 million year old Laetoli footprints from Ethiopia, thought by scientists to belong to Lucy’s species, Australopithecus afarensis, or something closely related to it. Creationists in general, and Answers in Genesis in particular, have always claimed that these are same as small modern human footprints (e.g. here, or here). The new paper however contains some evidence against that claim.

Naturally, Bennett and his colleagues compared the Ileret and Laetoli footprints, and concluded that:

Bennett et al. wrote:

… these [Ileret] prints are also morphologically distinct from the 3.75-million-year-old footprints at Laetoli, Tanzania

A comparison of the instep width relative to the width in the metatarsal head region shows that the upper prints at FwJj14E [Ileret] fall within the modern human range and are distinct from the relatively wider insteps characterizing the Laetoli prints (Fig. 4C).

When compared to the Laetoli prints, the Ileret prints have a more contracted proximal mid-foot region, including a deeper instep (Fig. 4D), suggesting the presence of a medial longitudinal arch. The location of the narrowest point of the instep also lies farther forward (more distal) in the Laetoli prints than in both the modern and Ileret prints, possibly reflecting differences in foot proportions or a lack of definition of the instep.

In other words, contrary to the previous claims of creationists, the scientists found a number of significant differences between the Laetoli footprints and H. erectus (or sapiens) footprints.

And although the Ileret H. erectus individuals walked identically to modern humans, Bennett et al. did report one small anatomical difference between them and us:

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).

(The hallux is the big toe, and abduction is the action of pulling the toe away from the line of the foot. Not to be confused with the opposite action, which is called adduction.)

The online supplementary material for the paper also shows that the creationist spin on the Laetoli footprints is way, way oversimplified. There is a wide range of opinion about the Laetoli prints, only a part of which is consistent with the creationist interpretation:

Bennett et al. wrote:

The interpretation of the Laetoli footprints has been and continues to be a matter of debate over whether they represent an essentially modern bipedal gait (S5-S9), a primitive gait (e.g., bent-hip, bent-knee) or unique form of gait (S10-S12), or whether the evidence to date is ambiguous (S13). Debate also continues over the interpretation of anatomy from the prints, with some researchers arguing that they point to a primitive foot structure bearing a slightly abducted hallux, relatively long, possibly curled lateral toes, and lacking both a medial longitudinal arch and evidence of a medial weight transfer (S10,S11,S14). Others instead argue that the Laetoli prints show evidence of a relatively modern human-like foot anatomy with evidence of a medial longitudinal arch (S5-S8), and these researchers point to the considerable variation in footprint structure, including variations in the degree of hallucal abduction and longitudinal arch height in the prints made by habitually shod and unshod modern humans (S6). Our study supports the hypotheses that the Laetoli prints were made by a foot whose hallux was much more adducted than in apes, but slightly and significantly more abducted than that of modern humans (Fig. 4A), with little positive evidence of medial weight transfer prior to push-off, or a longitudinal arch comparable to that seen in modern humans (Fig. S16). There is little doubt that compared to the modern great apes (S11, S15) the Laetoli prints and the hard tissue anatomy of contemporary hominins show evidence of a foot adapted for bipedalism including a more rigid tarsus but debate continues over whether the Laetoli footprints provide evidence of a modern human-like longitudinal arch (S6,S11).

But, of course, Answers in Genesis readers won’t be hearing about any of that…