If there’s one thing that paleontologists can say for certain about human evolution, it’s that we evolved from hominids who lived millions of years ago. We’ve all heard about the Neanderthals, Homo erectus and Homo sapiens, but can we ever be sure which of these species evolved from which? Which major species are we really descended from? And most importantly, what does evolution really show about the differences between modern humans and their ancestors, and what characteristics we can truly call “human?”
An approximately 3 million-year-old fossil of a skull, uncovered by quarrymen in South Africa in the 1920s, was initially accepted as a missing link between early hominids and modern man. But many doubted anthropologist Raymond Dart’s classification of the fossil as a completely new species, Australopithecus africanus, or the “southern ape from Africa. The species was supposedly related to both apes and men but was extinct with direct living descendants.
Early scans and reconstructions of the fossil revealed that it belonged to a three or four-year-old child with a small but complex brain and small teeth. This further weakened the initial claim that the Taung Child, as the fossil was soon dubbed, was truly an ancestor of modern day man. Existing research and fossil finds had determined that humans had begun to evolve as a separate species from as early as 30 million years ago, and the overwhelming belief of the time was that humans had large, heavily specialized brains. Thus, many scientists doubted that the historically young Taung Child could be related to modern humans.
Some members of the scientific community continued to accept that the Taung Child was an ancestor of Homo sapiens. However, a group of anthropologists and brain scientists have now published a study that reveals a distinct difference between the skulls of the Taung Child and modern human children and infants. Kristian J. Carlson, Ralph L. Holloway and Douglas C. Broadfield used computed tomography (CT) to “dissect” the skull electronically, revealing the lack of a persistent metopic suture and an open anterior fontanelle. These features are openings or temporary weaknesses in the skull, present in young human children, that allow it to expand, facilitating early and rapid brain growth. Their absence in the Taung Child shows that the development and expansion of the brains of Australopithecus africanus adapted differently from that of Homo sapiens, favoring certain characteristics over others.
The study implicates that the Taung Child’s brain did not experience an expansion of the prefrontal lobe, a brain area that is now considered unique and distinctive to humans due to its repeated linkage to human behaviors and intelligence. But does the lack of this development in Australopithecus africanus characterize it as a more modern one, unique to the most recent evolution of our species? Or does it suggest that humans did not actually evolve with a preference for larger prefrontal lobes and more specialized behaviors? Whatever conclusion is accepted, there’s definitely something new that scientists can agree on: The evolution of our species, and what makes us human, is much more complicated than we’ve assumed in the past.
