White also predicted that “the Laetoli prints will eventually be shown to be subtly distinct from those left under analogous conditions by anatomically modern humans” (White and Suwa 1987, pp. 510, 512). But as far as anyone can see now, they are indistinguishable from those of modern humans. Even White himself once said: “Make no mistake about it. They are like modern human footprints. If one were left in the sand of a California beach today, and a four-year-old were asked what it was, he would instantly say that somebody had walked there. He wouldn’t be able to tell it from a hundred other prints on the beach, nor would you. The external morphology is the same. There is a wellshaped modern heel with a strong arch and a good ball of the foot in front of it. The big toe is in a straight line. It doesn’t stick out to the side like an ape toe” (Johanson and Edey 1981, p. 250).
And Tuttle (1985, p. 130) noted: “in all discernible morphological features, the feet of the individuals that made the G trails are indistinguishable from those of modern humans.”
11.11 Black Skull, Black Thoughts
In 1985, Alan Walker of Johns Hopkins University discovered west of Lake Turkana a fossil hominid skull stained dark by minerals. Called the Black Skull, it raised questions about Donald Johanson’s view of hominid evolution.
According to Johanson, Australopithecus afarensis
gave rise to two lines of hominids. This arrangement can be visualized as a tree with two branches. The trunk is Australopithecus afarensis. On one branch is the Homo line, proceeding from Homo habilis to Homo erectus to Homo sapiens. On the second branch are the australopithecines arising from Australopithecus afarensis.
Johanson and White claimed that Australopithecus afarensis
gave rise to Australopithecus africanus, which in turn gave rise to Australopithecus robustus. The trend was toward larger teeth and jaws, and a larger skull with a ridge of bone, the saggital crest, running lengthwise along the top. The saggital crest served as a point of attachment for the powerful jaw muscles of robust australopithecines. Australopithecus robustus then supposedly gave rise to the superrobust Australopithecus boisei, which manifested all the above-mentioned features in an extreme form.
In an article titled “Baffling Limb on the Family Tree,” Walker’s wife Pat Shipman, also of Johns Hopkins University, explained the evolutionary significance of the Black Skull, designated KNM-WT 17000.
The first specimens of Australopithecus robustus
were, it was thought, about 2 million years old (Johanson and Edey 1981, p. 283). But the Black Skull, with its Australopithecus boisei features, including the largest cranial crest of any hominid (Shipman 1986, p. 91), was 2.5 million years old. Shipman believed this meant that Australopithecus boisei and the boisei-like Black Skull could not be descended from Australopithecus robustus, as believed by Johanson and others.
So where does that leave us? Here is one possibility suggested by Shipman. On our hominid family tree, we could now go from Australopithecus afarensis
up one branch to Australopithecus africanus. Then from Australopithecus africanus could come two separate branches. On one branch is Australopithecus robustus and on the other Australopithecus boisei and the boisei-like Black Skull. In other words, instead of deriving Australopithecus boisei from Australopithecus robustus, both originate from Australopithecus africanus.
But perhaps not. “All known africanus
skulls share many features that are derived, i.e, advanced, relative to those of the new skull, such as a moderate flexion or angling of the base of the cranium and a deep jaw joint with a bony lump in front of it,” said Shipman (1986, p. 91).
So, according to Shipman, another possibility now emerges—that Australopithecus africanus,
although ancestral to Australopithecus robustus, might not have been ancestral to Australopithecus boisei and the boisei-like Black Skull.