How our species appeared on this planet has traditionally been a touchy subject. For centuries different religions pushed their creation myths as the answer to the persistent question “How did we come to be here?”, but as naturalists examined the world around them the less the “Book of Nature” fit with the classic stories. Now, through our understanding of evolution, we know that our species was not produced in some divine fiat but represents a lonely twig inextricably connected to all other life through our ancestry.
Despite what we have come to learn about the origin of our species, however, I would wager that few members of the public know very much about human evolution. It can be a blow to one’s pride to recognize the monkey in the mirror, and despite all the fantastic discoveries that have been made in recent years human evolution is a subject that many people seem content to avoid. For those who are not so offended at the thought of being closely related to chimpanzees, however, next month PBS is going to launch a three-part series called Becoming Human that summarizes our present state of understanding on human origins.
I have to admit that the first installment made me cringe almost immediately. “What set us on the path to humanity?” the narrator asks at the beginning of Part 1. Along with the concept of the “invasion of the land” associated with the origin of the first terrestrial vertebrates, allusions to some vaunted “path to humanity” is one of my pet peeves when it comes to the popularization of evolution. The phrase makes it sound as if some lowly Miocene ape decided that it wanted a better life and set off on a heroic journey to become human. It is an attractive concept, but it is one that places human exceptionalism over what we actually understand about evolution.
The “March of Progress” theme permeates the documentary, but I will not delay to dissect it any further. (If you feel in need of further enlightenment on the subject I suggest picking up something by Stephen Jay Gould.) With the introductory synopsis out of the way the documentary picks up with Zeresenay Alemseged and the discovery of “Selam“, an infant Australopithecus afarensis discovered in the Afar region of Ethiopia. The complementary profiles of the scientist and the fossil provide a good way to briefly introduce a recent important discovery and drive home the depth of the human fossil record.
Picking Australopithecus afarensis as a starting point might seem a little odd at first (why not start at the very beginning, or work backwards from the present?), but it makes sense. As Donald Johanson suggests in a soundbite, Australopithecus afarensis possessed a mosaic of archaic, arboreal adaptations and more specialized characteristics that related her closely with early members of our own genus, Homo. Thus Australopithecus afarensis allows the filmmakers to establish that traits we see in our own skeletons are actually millions of years old, bridging the anatomical gap between our ape ancestors and us.
This transitions into a discussion of how the ecology of eastern Africa changed over time, particularly the dwindling of rainforests and the expansion of more open habitats. This, of course, is meant to set the stage for a discussion of bipedalism. Chimpanzees are used as models for what the earliest hominins were like, something that the description of “Ardi” (which was released after this program was almost entirely completed) disputes, but walking on two legs is still treated as something of an exaptation. The earliest hominins could walk on two legs in a relatively inefficient manner, but bipedalism only became “locked in” as a human trait, the documentary suggests, because it was a more energetically cost-effective way of moving in the increasingly open world early hominins inhabited.
After a brief overview of how genetics changed idea about the relationship between apes and humans (namely, that we are apes) the documentary asks what the last common ancestor between chimpanzees and humans was like. Sahelanthropus, depicted as a knuckle-walker in the graphic despite what its discoverers suggest were bipedal traits, is introduced as a potential human ancestor. To its credit, the program does mention that not everyone agree about the anatomy or evolutionary relationships of this hominid, but it was disconcerting that Orrorin and Ardipithecus were not even given a nod.
After introducing Sahelanthropus and Australopithecus afarensis the documentary briefly surveys the diversity of extinct hominins. The primary purpose of his overview is to say that despite the diversity of early hominins, brain size, that most cherished of human traits, did not change very much among the australopithecines. Indeed, for the next portion of the show the focus is on the brain, and the documentary states that its enlargement heralded “our era”, the reign of our genus Homo, beginning with Homo habilis.
The emergence of our “big brains” is then correlated with fluctuations in the landscape during the time the first members of our genus lived. The implication is that cycles of drought and inundation would have somehow made our ancestors more adaptable and triggered the evolution of a more “human” type. A brief mention is made that other hominins lived during the time of these fluctuations, but it is suggested that intense climate change drove them all to extinction. The survival of the earliest members of our genus in the wake of climate change is deemed to be the result of better problem-solving abilities, but the show does not actually explain why this would be so. It underlines correlation but makes no effort to establish causation.
Despite my annoyance at the documentary’s underlying theme of a blessed road that guided apes to the celebrated human form, it is a fair introduction to early human evolution for those who know that “Lucy” is important for understanding our origins but cannot quite articulate why. There is plenty of interesting information that did not make it into the documentary, and some adaptive scenarios in the show should be considered critically, but overall it will provide a good starting point for those who wish to know more about human evolution. I will review Part 2 next week.