By Prof. Dean Falk, Department of Anthropology,
The State University of New York in Albany.
Several million years of natural selection has given human beings a prodigious ability for processing and communicating information. Because of their large size, intricate wiring, and delicate balance of neurochemicals, human brains are uniquely capable of abstracting, synthesizing, and interpreting vast amounts of stimuli. Unlike other primates, the mental ruminations of people are tempered by a keen sense of time and are easily communicated using representations constructed from linguistic, musical, and visual symbols. Consequently, human minds are capable of wonderful endeavours - like worrying about the origin of the Universe, finding the solution to a complex problem in an intuitive flash, or visualizing the face of a long-lost loved one.
But how are we to know about the brains, and minds of our early relatives, the australopithecines? Although this might seem like a hopeless task, at least until a time machine is invented, it is not. The outside portion of the brain, or cerebral cortex, is the part most responsible for the mental complexities that distinguish humans from other primates. For this reason, important clues may be gleaned from imprints left by the cerebral cortex on the inner surfaces of fossilized australopithecine skulls. Casts of such braincases (called endocasts) provide information about the size of specific lobes of the brain and their pattern of convolutions and blood vessels. Fossilized skulls are usually fragmentary, and an entire australopithecine endocast is a rare prize. Each new discovery of even a part of a fossilized braincase therefore has the potential for adding greatly to our knowledge about australopithecine cerebral cortices.
Several relatively recent discoveries of australopithecines have yielded parts of endocasts that were previously unknown for some of the species that lived in Africa; approximately 1.0 to 3.5 million years ago. My colleagues and I (Falk et al., 2000) have recently studied these endocasts with fascinating results. In one of the four australopithecine species that were studied, certain parts of the cerebral cortex appeared advanced compared to the brains of living great apes. Coincidentally, this species (Australopithecus africanus, commonly called gracile australopithecines) happens to be the first that was described by South African anatomist Raymond Dart, in 1925. Endocasts from A. africanus reveal that its brain size was, on average, within the range of living chimpanzees. The underneath surfaces of its frontal lobes and the anterior tips of its temporal lobes, however, appear to have evolved to a point that was intermediary between the forms seen in great apes and humans. In other words, the cerebral cortex of this species was unlike that of any living primate!
Because they have long been extinct, one can only speculate about what gracile australopithecines were doing (or thinking) with the swollen parts of their frontal and temporal lobes in light of the known functions of these areas in humans and chimpanzees. In both of the living primates, the part of the frontal lobe that is enlarged in australopithecines is important for keeping simple tasks in mind long enough to complete them. In humans, however, this area is also involved in much more complicated tasks such as undertaking complex initiatives, highly abstract thinking, and making plans for the proverbial rainy day.
Was A. africanus using its expanded frontal lobes to formulate abstract ideas and make plans that no chimpanzee could ever imagine? In both chimpanzees and people, the tips of the temporal lobes have connections with the frontal lobes, the left of which processes speech in humans. Interestingly, in humans, the tips of both temporal lobes are activated the instant a name is attached to a familiar face. Wild chimpanzees, of course, do not have a human-like language with which to name other individuals or concepts. Since naming of familiar faces is universally one of the first steps human infants take as they develop language for eg.mama, dada, the expanded temporal lobes of gracile australopithecines may be of special significance from an evolutionary perspective.
Could it be that the unique combination of features seen on gracile australopithecine endocasts reflect the first glimmerings (naming) at the beginning of a long and complex evolutionary journey that eventually led to present-day language, biotechnology, and space exploration? Although paleoanthropologists continue to engage in lively debates about which australopithecine species, if any, may actually have been a direct ancestor of Homo sapiens, the evidence from endocasts suggests that A. africanus is one of the more likely possibilities.
Falk, D., Redmond, J.C., Jr., Guyer, J., Conroy, G.C., Recheis, W., Weber, G.W. and H. Seidler. Early hominid brain evolution: A new look at old endocasts, J. Hum. Evol., In press.(2000)
Read a biography of Prof. Falk.
Maintained by Francis F. Steen, Communication Studies, University of California Los Angeles