David Pilbeam's Foreword to -

The Upright Ape:

A New Origin of the Species

           I first met Aaron Filler when I joined the Harvard faculty in 1981, and enjoyed interacting with this stimulating polymath as he wrestled with his doctoral research topic on the evolution of the variety of ways apes, humans, and their ancestors moved--through the trees and on the ground.  How animals move (or "locomote" in technical jargon) is critical to understanding a species' biology, for moving is vital to feeding, finding mates, and avoiding predators, and hence for survival and reproduction.  Aaron is now Dr. Filler, and a distinguished neurosurgeon.  But in the two decades since completing his doctorate, he has continued to think not only about what happened in the locomotor evolution of apes and humans (technically, "hominoids"), but how it happened developmentally, and why it happened in terms of selective advantage.

            After a century and a half of controversy, the evolutionary relationships of the few surviving hominoid species are well established through abundant genetic analyses of these living species.  Humans are closest relatives of the two chimpanzee species, while the African gorillas (which resemble chimps closely and look in many ways like enlarged versions of their smaller African cousins) are more distantly related.  The large Asian orangutan is still further removed, while the small and acrobatic Asian gibbons are the most distantly related of all the hominoids.  It is now believed that these living hominoids share a common ancestor that lived over 20 million years ago.  Although these relationships are now very widely (though not quite universally) accepted, almost every possible combination of relationships among the species had been proposed over the past century.

            There have been almost as many suggestions about the locomotor evolution of these species, but almost all have agreed that the defining feature of humans and their ancestors after the split from the chimpanzee lineage was bipedalism--habitual upright walking.  To be an habitual biped requires a whole suite of anatomical adaptations (special features shaped by natural selection).  The large apes--chimps, gorillas, orangutans, are occasionally bipedal, but also use many other movement patterns.  Among the hominoids, it is the small gibbons that are most frequent bipeds, although other ways of moving are more frequent in their repertoire.  Over a century ago, before our modern understanding of hominoid evolutionary relationships, the distinguished anatomist Arthur Keith proposed that bipedalism was a constant theme throughout hominoid evolution, and not just in the evolution of our own lineage.  This model has fallen out of favor, and it is now more widely accepted, though not universally, that the common ancestor of humans and chimps would have been quite chimp-like (and gorilla-like), moving in the trees by vertical clambering and arm suspension, and on the ground quadrupedally with feet flat and toes extended and fingers curled so that knuckles contact the ground; bipedalism would have been very infrequent.

            Dr. Filler brings a refreshingly contrarian approach to these questions.  His research involves careful anatomical observation, the analysis of critical fossils, along with developmental biology of the spine (indeed he was one of the very first to bring the then barely nascent field of evolutionary developmental biology to bear on a problem in human evolution), blending them into a novel theory.  Briefly, he argues that bipedalism has always been an important component of the locomotor behavior of all living hominoids since their common ancestor evolved such behaviors (along with corollary and  necessary anatomical and developmental adaptations).  Dr. Filler discusses in detail the anatomical and developmental bases for his argument.  As he points out provocatively, if some significant degree of bipedalism precedes the divergence of humans and chimps, this raises most interesting questions about the recognition, interpretation, and definition of the earliest possible human ancestors.

            This book is bound to stimulate; its arguments are challenging, may not be widely accepted, but will need to be taken seriously.

David Pilbeam

Henry Ford II Professor of Human Evolution

Peabody Museum

Harvard University   

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