Voices from the Past (2)

By Bernard Wood
July 31, 2018

Louis Leakey’s presentation of the results of research at Olduvai was the focus of the The Origin of Man symposium sponsored by the Wenner-Gren Foundation for Anthropological Research, which was held between April 2nd- 4th, 1965, at The University of Chicago1. Although Louis Leakey’s presentation was characteristically provocative, the discussion that followed was not contentious, with most questioners seeking clarification about the geological context of the fossil evidence. The fireworks began in the next session, entitled Evaluation of the Olduvai Discoveries.

The first speaker was Garniss Curtis who, together with Jack Evernden, was responsible for applying the relatively new potassium-argon method to dating the igneous rocks that are interspersed among, or lie below, the sediments containing the hominin fossils. Curtis’ presentation is a master-class in explaining in simple terms the steps involved in identifying contamination, and the way the two geochronologists collaborated with Richard (Dick) Hay to identify the sources of the least contaminated tuffs.

Basil Cooke, a paleontologist, responded in a characteristically robust fashion, prefacing his remarks by stating—not very diplomatically—that “these dates worry me a good deal” (p. 23). His concern seemed to stem from what he perceived to be a mismatch between the ages of the minerals in the tuffs and lava flows, and the thickness of the sediments, suggesting that “if the dates are correct, the deposition must have been extremely intermittent” (ibid). Jack Evernden— who confessed that “understatement” was “not one of my failings” (p. 27)—mounted a robust defense of the dates generated by the Curtis/Evernden team. He also pointed out to Cooke and the audience that it is unreasonable to assume “that every interval of time from 1.76 million to 500,000 is represented by its increment of sediment,” and he confirmed that he and Curtis had concluded that large intervals of time” are “not represented in the sequence” (ibid). But the exchanges between Cooke and Evernden were just a “warm-up act” for what was to follow.

 

Robinson

As far as Leakey—and the attendees in the know—were concerned, the “elephant in the room” was John Robinson (pictured here, on the left, at Sterkfontein with Robert Broom). Remember that in the January 9th issue of Nature2, less than three months before the gathering in Chicago, Robinson had published a scathing critique of Leakey, Tobias and Napier (1964). In essence, he complained that Homo habilis was the result of conflating earlier fossils belonging to Australopithecus with later ones belonging to Homo erectus. Robinson’s contribution, and the inevitable ensuing exchange with Louis Leakey, must have been eagerly awaited.

In the event Robinson’s presentation, as captured by the transcript, is a model of civil discourse, and reasoned and careful argument. He began by complimenting “Dr. Leakey and his co-workers” on the “extremely valuable and exciting material that is becoming available from Olduvai” (p. 29). But in what should become a classic example of understatement, Robinson suggested that “there are some points of interpretation that one feels a bit bothered about” (ibid).

One of the contentious “points of interpretation” involved the relatively small size of the sample of hominins from Olduvai compared to the larger samples from southern Africa that Robinson was used to dealing with. Robinson reminded the attendees that when samples are small, there is an inevitable distinction between the range of variation observed in the fossils recovered, and the range of variation “in the original population from which the fossil sample was drawn” (p. 31). He also made the perceptive observation that there seemed to be more variation in the samples of southern African hominins assigned to Paranthropus than there was in similar sized samples of fossils allocated to Australopithecus.  Robinson also reprised the arguments he made in his Nature paper by suggesting that “there are better morphological grounds” for distinguishing the Bed II material attributed to Homo habilis from the Bed I material attributed to that taxon, than there are for “distinguishing either Bed I —material from South African Australopithecus or Bed II material from something like “Telanthropus”(=Homo erectus)” (ibid). For Robinson, at both Olduvai and at the southern African cave sites, the morphologically relatively invariant Paranthropus lived alongside a more variable second lineage. During the same period the former lineage shows little evidence of morphological change (i.e., it provides an example of stasis), whereas within the latter lineage there is more substantial evidence of morphological change, with Australopithecus evolving—anagenetically—into Homo erectus.

The first person to comment on Robinson’s presentation was Clark Howell, who said he “agree(d) completely with Dr. Robinson’s conclusions” (p. 33) and was of the opinion that the fossils from Olduvai captured the transition from Australopithecus to Homo erectus. Louis Leakey pushed back against both Robinson and Howell, suggesting that they had failed to recognize differences between the mandibular and premolar crown morphology of Australopithecus and Homo habilis. Robinson responded by suggesting that “the argument is not whether one can detect some difference but what the significance of the difference is” (p. 37). Louis Leakey’s irritation with Robinson’s alternative interpretation, also emphatically supported by Clark Howell, is evident from the back and forth between the protagonists.

What is striking about these exchanges is that they reflect differences in interpreting the hominin fossil record that are alive and well more than half-a-century later. True, methods for capturing and quantifying morphology are more sophisticated now than they were then, but when all is said and done we are still grappling with Robinson’s point that relatively small site samples of taxa do not capture the range of variation in the populations from which those samples are drawn.

As the Latin tag nihil sub sole novum suggests, truly there is “nothing new under the sun”!

https://cashp.columbian.gwu.edu/voices-past

2Homo ‘habilis’ and the Australopithecines. (1965) Nature, 205: 121-4.