Amongst other things, Filler explains how the design of the lumbar region (between the pelvis and the ribs) of modern humans - apparently adapted for a predominantly upright stance - closely resembles that of the 21.6 million-year-old ape Morotopithecus bishopi .

Chimps and gorillas don't have "a" different design but two different arrangements for bracing the back against sagging when on all-fours.

Had humans evolved from some quadrupedal ancestor we shared with chimps and gorillas, the latter two would be expected to resemble each other more and humans would be expected to resemble Morotopithecus less.

In fact, no predominantly quadrupedal apes close to human ancestry are known after Proconsul which preceded Morotopithecus.

The most shocking thing about this is the way the major lesson of this paper has been ignored since the material first appeared in his 1986 PhD thesis. It combines with other evidence - the lack of overlap between chimp/gorilla fossils (teeth tell little about quadrupedality and are highly variable anyway), and those of australopithecines - that all point to chimps and gorillas (and orangs) having become quadrupedal independently, and the line to humans having been continuously bipedal since sometime between Proconsul and Morotopithecus.

The commentary at...
http://www.amazon.com/Axi...
...for example fails to appreciate the basic lesson Filler tries to teach us about human bipedality. It is easy to see why the more casual palaeoanthropologists amongst us don't realise chimps and gorillas sprang from australopithecines since they've never been allowed to see the theory and don't know all the background, but why on earth do professionals, who should be well briefed on most aspects of the story, carry on believing that great apes and man came from common quadrupedal stock? (They must have heard of Gribbin and Cherfas' book "The First Chimpanzee", and there really is no convincing evidence that the chimp/human split was nearer six million year ago than four.) The situation is worse than that since the superior alternative is almost never mentioned in discussions on human evolution, almost as if it so dreadful as to be unscientific. While we should not underestimate the contribution fear of derision by other enthusiasts or those influential in the profession makes, the simple lack of understanding of what science is and how to choose between theories may well be the main culprit. People just don't know that the best theory is the one that explains or predicts the best - no more, no less. All those characters in museums and anthropology departments around the world who never mention the ex-bipedal great apes theory to their visitors and students, and worse still, those science editors who insist it is never mentioned, are simply advertising their ignorance either of the evidence or of the nature of science - in other words, they are not scientists in the modern sense. This whole business also highlights the paramount importance of philosophy of science to science. A scientist who gets their philosophy wrong can expect and will deserve to waste their day - or their entire career - as well as the money they're paid to do the job, and the efforts of those who trust them for guidance.


It's worth commenting on Filler's view that the developments in vertebral designs he details were in some sense crucial for whole lines of evolution to become possible, almost as if for example chimps would never have become quadrupedal if their particular vertebral modifications had not happened. On early mammals he says:
"This is an excellent candidate explanation for the odd pattern of total absence in the fossil record of any mammals much larger than one or two kilograms for the first 160 million years of the existence of this group followed by an explosion of diverse large body mammalian forms in the last 60 million years. Homeotic change that led to diminutive lumbar ribs in the early
mammals increased lumbar flexibility for sagittal excursion during symmetric gaits, but seems to have left these groups without the mechanical support in the lumbar region required for the
architecture of a large animal."
Many people will prefer the view that while a few mutations or adaptations play a leading in role in subsequent evolution - powered flight for example - more trivial details are simply what evolution happened upon first when a new niche opened up. When it became favourable for multiple branches of australopithecines to become quadrupedal, adaptations were quickly and simply adopted with the ease of a chimp walking up a tree.

Another thing that caught my eye in this paper was the way he describes the very high placement on vertebrae of lateral projections as characteristic of archosaurs' (birds, crocs, dinosaurs, pterosaurs, thecodonts) lumber region and elsewhere. In this design, tension applied between these lateral projections will tend to extend the spine (make it dorsally concave) and is a characteristic of bipeds. Now why would basal archosaurs want this?