The Adventures of Zakariah Khan

Preface

From Apes to Humans

It all started at the turn of the century, when the science of paleoanthropology was beginning to come into its own and fragments of fossilized hominids were being unearthed all around the globe. Initially, when these specimens were scarce, the general consensus among the paleoanthropologists was that the most important differentiating feature between apes and humans was the size of the brain. This was determined by various methodologies, ranging from crude assessments out in the field by pouring sand into the skull cavity and gathering it up in a measuring cylinder, to endocasts of crania obtained by the painstaking reconstruction of hominid skull fragments, isolated from lumps of petrified earth.

But, the subsequent rapid accumulation of relevant fossil evidence quickly made this viewpoint untenable and various alternative hypotheses were proposed to fill in the vacuum. A few decades of vocal debates ensued, which finally culminated in the conclusion that even though brain size was an important criterion, it occurred later on in hominid evolution and that it was, initially, the adoption of a fulltime upright stance that helped launch the human species on the road to success.

It was generally thought that the adoption of bipedalism was in part precipitated by major fluctuations in the world climate at about the 7 to 5 million year ago (mya) time span, wherein the dense forests in which our ancestors dwelled, rapidly gave way to grassy woodlands interspersed by wide open spaces. This perturbation of the environment was implicated as a major factor in the debut of a humanlike subspecies from a population of hominoids that had colonized this closed ancestral forest environment.

In the mid to late 1970’s, hominid fossils were unearthed both in the Hadar region of Ethiopia and at Laetoli in Tanzania, that were older than any other hominids then known. Before Don Johanson found Lucy (A. afarensis), in 1974, most anthropologists have accepted the ‘fact’ that the Taung baby (A. africanus), found in 1924, by Raymond Dart, was the original or first hominid. Then, in 1978, Mary Leakey found a trail of hominid footprints at the Laetoli site in Tanzania. These were dated to be more than 3.5 million years old and thus became the earliest evidence of upright walking by the hominid species.

Since these early hominid prints were made by upright humanids from the same species as Lucy (confirmed by the presence of other similar fossils found in the same region), the scientists now believe that full-time bipedalism in humans could have arisen even earlier, as the bipedal ‘stride’ evident in the Laetoli prints, is almost indistinguishable, from that of modern humans living today.

            The rationale for this type of thinking is that just as the human gait evolves, from the tentative first steps of a one-year old, to the firmer, more-confident stride of a four-year old, the first family of Laetoli fame, were already well-established in their adaptation to walking upright, fulltime. Based on this hypothesis, the early hominids may have adopted the bipedal gait as far back as 4.5 or even 5 mya.

            Recent discoveries in both Ethiopia and Tanzania, suggest that archaic Homo had existed for perhaps as much as a million years prior to 5 mya and that it was fairly well spread-out throughout East Africa, i.e. all that region east of the Great Rift Valley. Interestingly, this date matches remarkably closely with the split-date of 5 to 6 mya between humans and chimps, arrived at by the molecular geneticists, based on DNA analyses and blood-protein serological studies.

            Dr. Lovejoy believes, from a study of Lucy’s leg and foot bones that by the time Lucy was alive, the fulltime upright stance had been established for as long as two million years.  He also asserts that Lucy and her cohorts were ‘confident and effective’ on two legs and came from a long line of bipedal ancestors.

            The fossilized jawbones of A. afarensis have much in common with those of the great apes in size, shape of the teeth and the structure of the face.  The shape of the head is still relatively ape-like i.e. the face projected forwards, the brain is small (approx. 450 cc) and the canine teeth are quite large and curved.

            Proportionately, the legs were thought to be quite short and the arms, relatively long.  The fossil hand bones showed that A. afarensis was probably almost as dexterous as modern humans and the absence of grasping toes would have made Lucy, unable to climb trees, effectively.

            Lucy had the human-like characteristics of a full-time upright stance, arched feet and relatively long thumbs.  But, she also had the ape-like features of small size (less that 4 ft. tall) short legs, long arms, somewhat hunched shoulders and moderately curved fingers.  It had a small brain, did not speak in words and did not yet make stone tools.

So…was Lucy… human or just an upright, full-time bipedal ape?

What is it that truly differentiates us, humans from the rest of the great apes? Is it the fact that we are able to walk upright or is it our larger cranial capacity? Or is it our innate intelligence?

As it turns out, it is none of the above. There are many examples of upright walking in the animal world and quite a few of the mammals have larger brains than other creatures, but we still consider them, animals. Some species also display