American Museum of Natural History
- Dr. Ian Tattersall pieces together the human past
- Seven million years of human evolution
- Understanding our past: DNA
- What is the evidence for human evolution
- Searching for Human Ancestors in East Africa
- Expedition Rusinga—uncovering our adaptive origins
- Quiz: Human evolution
- Exploration Questions: Human evolution
- Answers to Exploration Questions: Human evolution
"For many years human evolution was looked on as sort of single-minded slog from primitiveness to perfection," says Dr. Ian Tattersall, emeritus curator of anthropology at the American Museum of Natural History. "But as the human fossil record has grown by leaps and bounds, we've found that the pattern seems to have been one of experimentation from the very start. Rather than the culmination of a linear process, humans are much better viewed as the single surviving terminal twig on a very luxuriantly branching tree."
Groups of early hominins—the lineage that split from chimpanzees—first appeared in Africa some 6 or 7 million years ago. Following this, the hominins diversified considerably, but all eventually went extinct, with the exception of modern humans, or Homo sapiens. "That tells you there's something very special about Homo sapiens," says Tattersall. (Humans are not the only species that sits alone at the end of its branch, of course. For example, aardvarks, koalas, and tuataras are all the only representatives of their respective branches: order Tubulidentata for aardvarks, family Phascolarctidae for koalas, and order Rhynchocephalia for tuataras. However, most species share their branches with other living species.) "It is a very unusual situation for there to be only one hominin species," says Tattersall. He theorizes that its newly acquired ability to process information symbolically is what allowed Homo sapiens very rapidly to eliminate all hominin competition worldwide, following about 40,000 years ago.
How do we study the human fossil record?
Finding and analyzing fossils is a complex task that typically requires a team of paleoanthropologists (scientists who study the evolution of the human species), geologists, anatomists, and paleoecologists—to name just a few. To piece together the story of how ancient peoples lived and died, these experts analyze artifacts, sediments, plant and animal remains, and DNA evidence.
Noting that the process of studying ancient hominins is the same as for any other kind of mammal, Tattersall observes that luck is as important as logic when it comes to fossil hunting. For example, paleoanthropologists are currently hard at work at Dmanisi, a 1.8-million-year-old site in the Caucasus, the earliest place outside of Africa where a hominin presence has been documented—and "not a place where anybody would have imagined looking," he notes wryly. Dmanisi was the site of a prosperous town in the Middle Ages that was sacked by Mongols in the 13th century and abandoned. When archaeologists specializing in medieval history came along, they were astonished to find the ancient bones of much earlier inhabitants poking out of the walls of the basement pits used to store food.
Tattersall laments "the habit of complaining bitterly that we don't know enough and not appreciating that we have a fairly good fossil record, compared to many mammalian families." Fossils are almost invariably found in sedimentary rock, and the fact that humans typically lived near rivers and lakes, which give rise to sedimentary rock formations, helped protect their remains.
As the human fossil record expands, so does the need for standard descriptions and terminology. Along with his independent inquiries into modern human cognition, Tattersall has been working on a multivolume documentation of major hominin fossil finds that will serve as a database for further analyses of hominin systematics.
The challenge of early human history
Although exciting hominin finds are being made almost every year, much about human history remains controversial. There are currently several conflicting theories about the origin of the hominin family itself, "and frankly, we don't know what the earliest hominin should look like, so we'd have difficulty recognizing it if and when we find it," Tattersall comments. Paleontologists differentiate species by comparing the same skeletal elements across fossils from different places and periods. Since it's very rare to find complete skeletons, accurate comparisons are rare or nonexistent. Nevertheless, by comparing thousands of hominin bone fragments, paleoanthropologists generally agree that there are 15 or more known hominin species and have grouped them into about five genera, one of which is Homo.
What's a "human," anyway?
"People have been using the word 'human' since long before they knew they had extinct relatives or, indeed, any close living relatives. So it's really an arbitrary distinction," says the anthropologist. "But I think most scientists would apply the term human to any member of the genus Homo." The earliest fossils that significantly resemble Homo sapiens go back to around 200,000 years ago. Although the new species appears to have behaved much like other hominins of the time, it differed skeletally: It had a tiny face tucked under a very large brain case, while apes have a big face in front of a very small brain case. In contrast to other hominins, some species of which survived for over a million years, over the last 50,000 years this upstart rapidly populated the entire globe.
How did human consciousness evolve?
Along with the dubious distinction of having eliminated all the competition, the trait that most dramatically sets modern humans apart is their symbolic consciousness. Only humans can mentally recreate the world using symbols and manipulate these symbols to create abstract realms of thought. For the past several years, Tattersall has been wrestling with the question of how this nuanced awareness evolved. "Neurologists think about neurons, paleontologists think about fossils, archaeologists think about artifacts, and it's very difficult to put it all together when it comes to studying human consciousness," the anthropologist points out. "The main point to remember is that you've got a fish brain, a reptile brain, a primitive mammal brain, and primate and ape brains inside your head. We don't know exactly how each of these ingredients contributes to the functioning of the human brain, nor to what we subjectively experience as consciousness. But we function as we do only because of all those layers supporting consciousness from beneath."
An anatomical change paves the way
Calling the retraction of the face in Homo sapiens "a lucky confluence with a lot of implications," Tattersall points out that "you need a certain morphology of the upper vocal tract and upper airway in order to produce articulate language." Clearly, the emergence of Homo sapiens as a physical entity represented a major developmental reorganization, and in the anthropologist's opinion, this set the stage for a major developmental leap: Physiologically capable of speech, the first Homo sapiens were also neurologically capable of symbolic thought. But the new species had yet to discover its potential.
Drawing the analogy that birds had feathers for millions of years before using them for flight, Tattersall thinks that the potential for symbolic thought had to be released by a cultural stimulus. "My suggestion, which is not original, is that this stimulus was probably the invention of language—the ultimate symbolic activity," he says. It's a difficult theory to investigate, but anthropologists know that languages are spontaneously invented, and Tattersall's guess is that children could have invented them in the context of play. While no one knows when humans started speaking, archaeological evidence of symbolic cognition first appeared by at least 77,000 years ago. Such evidence includes engraved pieces of ochre from a site in South Africa. Evidence of symbolic cognition is indisputably present by 40,000 years ago, in the traditions of representational art long known from Europe and now represented in Indonesia as well.
However we arrived at our extraordinary cognitive abilities, as far as we know we are the only species in the universe capable of considering our own evolution.
Want to join the conversation?
- Based on reading the last paragraph, I was wondering if it would be possible for scientists to genetically alter our human traits to give us, like, less human or supernatural traits, like in those science fiction books. If they could, would we be able to pass that on to our offspring?(3 votes)