“The question is whether we humans are simply aÃ‚ÂÃ‚Ân extrapolation of evolutionary trends, or if there is something truly new about our Ã‚Âspecies, Homo sapiens,” said Ian Tattersall, curator at the American Museum of Natural History, last Wednesday. Brought to campus by the Oakley Center, Tattersall delivered the Richmond Lecture titled “Becoming Human: Patterns of Innovation in Human Evolution.”
Tattersall is an expert in physical anthropology, specializing in the human fossil record, origins of human cognition, the study of ecology and the systematics of lemurs. Tattersall is the author of Human Origins: What Bones and Genomes Tell Us About Ourselves, The Monkey in the Mirror and Extinct Humans, among other books.
Throughout the lecture, Tattersall continually emphasized that hominid history, like that of all other successful primate history, has been one of diversity rather than a “linear grind to perfection.” As Tattersall explained, several different types of hominids have tended to coexist at any point in time, and the single species of Homo sapiens today is the “exception rather than the rule.”
Tattersall began the lecture by showcasing a number of paintings, starting with a “rather attractive” piece by the chimpanzee, Congo, followed by another painting by the elephant Ruby.
Tattersall next exhibited a work by the abstract expressionist Willem de Kooning, quipping that “humans haven’t come such an awfully long way in the last five or six million years.” Nonetheless, Tattersall remarked that the creative spark was the “distinguishing” element between Homo sapiens and other species, highlighting one theme of the lecture.
Walking down the evolutionary trail, Tattersall explained that fragmentary fossil records of the earliest creatures who were exclusively human ancestors and not those of both humans and apes date from seven to four million years ago. Found in Africa, these early human ancestors shared a common upright posture and bipedalism.
The first well-documented species, however, was Australopithecus afarensis, dating from 3.9 to 2.9 million years ago. Despite the bipedalism of Australopithecus afarensis, Tattersall remarked that there was “very little to indicate that early hominids were functionally human in any respect,” pointing to the ape-like proportions of their skulls and cognitive abilities comparable to those of today’s apes. In contrast, modern humans have smaller faces tucked under brain cases.
Continuing to the first recognizable member of the genus homo, Homo habilis, Tattersall discussed the crude stone tools possibly used by this “handy man.” In addition, Homo habilis had a slight enlargement of the brain relative to early bipedal species, although the brain size of Homo habilis still did not differ significantly from that of modern apes with comparable body sizes.
This led to Tattersall’s crucial point that behavioral innovations “do not tend to be associated with new kinds of hominid,” comparing new hominid behaviors to contemporary technological inventions created by individuals differing little physically from their parents.
Still, Tattersall acknowledged the “considerable insight” required to strike one cobble against another in order to detach a particularly-shaped flake.
At around 1.9 million years ago, a new species arose with body build and size comparable to that of modern humans, Homo ergaster.
While early bipedal apes were only three to four feet high, the Turkana boy skeleton discovered in northern Kenya had modern body proportions enabling him to top over six feet. Homo ergaster were long-limbed and slender, built for life far from the early forest habitats to live in the open savannas. Nonetheless, stone tools used by Homo ergaster differed little from those of Homo habilis.
From here, Tattersall discussed several other examples of early human species, including Homo erectus, Homo heidelbergensis and Homo neanderthalensis.
Finally, anatomically modern Homo sapiens arose in the Levant region 200,000 years ago. Within 10,000 years, modern Homo sapiens in the form of Cro-Magnon man had entirely replaced Neanderthals.
This, as Tattersall recalled, was the greatest shift in human cognitive history. “These people were us, possessed of sensibility totally unprecedented in hominid history, an entity with a restless appetite for change and complex symbolic activity,” he said. “What this shows is that Homo sapiens are not an extrapolation of earlier trends. We’re not a better version but something qualitatively different.”
In closing his talk, Tattersall briefly discussed the legacy of Charles Darwin and Alfred Russel Wallace. Darwin argued that the human brain was the product of a long accretionary evolutionary process. Wallace, on the other hand, favored chance acquisition. In fact, both were right in some way,
Tattersall concluded – ourÃ‚Â immediate ancestor must have possessed a brain that had evolved to the point where a single change or group of changes, such as the advent of language, could elicit radically new potential.
While the brains ofÃ‚Â the earliest humans looked exactly like modern humans for upwards of 50,000 years, the “potential lay fallow until discovered by a cultural stimulus,” Tattersall said.