“The skull just goes along for the ride.” “We think that an expansion of the soft brain tissue changes the shape of the hard skull bones, not the other way around,” notes McBratney. What caused these changes? No one has any samples of ancient brains to know for sure, but Lieberman and his colleagues believe that the alterations follow from an expansion of the temporal lobes of the brain, the areas that sit between the temples. The flexion, which coincided with a forward extension of the cranial base, also moved faces under the front part of the brain and eliminated heavy brow ridges. Lieberman shows its location by poking his finger through an empty eye socket and touching the bottom of that bony platform.Īccording to him, a sharper downward bend in the platform at a position near the temples makes modern skulls rounder than those of Neandertals and more ancient species. The major change appears in the cranial base, the plate of bone that forms both the roof of our faces and the floor of our brain case. Their analysis, published last month in the Proceedings of the National Academy of Sciences, showed only a few differences between modern skulls, and those of Neandertals and earlier human ancestors. The scans provided three-dimensional images of the sites of skull growth, joints where individual bony plates that make up the skull come together. Lieberman, graduate student Brandeis McBratney, and postdoctoral fellow Gail Krovitz took CAT scans of 119 human skulls, ranging from modern men and women to those hundreds of thousands of years old. “We don’t look at differences in pelvises or jaws, for example, but what we have come up with is a simple pattern that is unique to modern humans.” He and his colleagues focus on crania, the skull minus the jaw. “The problem is that some skulls that are clearly modern don’t have all the modern features and a number of clearly archaic skulls have some of these features,” Lieberman notes. That’s because skulls vary in obvious ways and many have survived as fossils. Modern humans differ from archaic humans in many respects, but anthropologists have been trying to define our species, Homo sapiens, based on the features of their skulls alone. “Our faces are not only smaller than those of the first modern humans but also smaller than those of our ancestors’ who lived only 300 years ago,” Lieberman points out. In humans, chewing softer, processed food also has contributed to reducing face size by decreasing the largeness of our jaws and jaw muscles. As the severe climate of the ice ages ended, the bodies and faces of most large animals have gotten smaller. These early alterations were followed by a steady decrease in human face and body size, which has been occurring over the past 10,000 years or so. Those changes would also move the face under the brain case, retracting the protruding face of our ancient ancestors and decreasing the size of their prominent brow ridge.” Just a handful of changes could shift the oblong, football shape of a Neandertal cranium to the rounded, soccer ball shape we see all around us today. “But it turns out that you don’t need to change many things to go from one skull type to the other. “It has long been thought that our skulls are extremely different from those of our ancient ancestors,” says the Harvard professor of biological anthropology. So far Lieberman has found some good answers and has come up with some controversial ideas. The hollow eye sockets, ancient teeth, and empty skulls pose the same question every day: What made us different from our archaic ancestors? The collection of skulls on his office shelves come from chimpanzees, long-extinct humans, and modern men and women. (Staff illustration by Alec Solomita )ĭaniel Lieberman can see millions of years of human evolution at a glance. The change from the oblong skull and protruding face of ancient humans (right) to the modern rounder skull and retracted face is associated with a sharper bend in the floor of the brain case (lower left), thought to be caused by increased brain size.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |