Estimating Cranial Capacity Essay Example for Free

Estimating Cranial Capacity Essay Human beings share approximately 94% of their DNA with their closest living relative, the chimpanzee. Yet, when one compares the proliferation and accomplishments of these two closely related species, one finds huge differences: human beings have spread across every continent but Antarctica; erected towers and pyramids hundreds of meters tall; crafted millions of beautiful works of art, literature, and music; travelled far beyond the Earth’s atmosphere, and deep into the crevices of its oceans; and engineered enough weapons to wipe the whole world of life. In contrast, chimpanzees have remained largely confined to their jungle habitats, and amongst their greatest accomplishments is the discovery that twigs can poke insects out of holes. So, if humans and chimpanzees are so closely related, what can account for such a huge difference in their abilities? One needs not think very hard to realize that the answer is brain-size. The chimpanzee brain is about half the size of the human brain, and this difference, of about 600 cubic centimeters, is the difference between sticks and space shuttles. Thus, because larger brains confer such an overwhelming evolutionary benefit in hominids, it is safe to say that a study of hominine brain size is no less than a study of hominine evolutionary advancement, as illustrated in the graph below, which is indicative of the results obtained from such studies. Fig 1: Scatter graph typical of results obtained when comparing cranial capacities of various species of fossil hominid. Since brain tissue deteriorates over time, the only way paleontologists can approximate the brain-size of extinct species is by studying the capacity of their fossilized craniums. This is known as craniometry. Given that it is such an important area of investigation, study into craniometry has been widespread and diverse, encompassing research from such eminent and eclectic figures as the evolutionary biologist T. H. Huxley and the physician and anthropologist Paul Broca. Although such studies vary greatly in their scopes and applications, almost all utilize one of two standard craniometrical methods: the glass-bead technique (and variations like the lead-shot technique) and the caliper measurement technique. Because craniometrical researchers rely so much on these two methods, it is important that the accuracy of the methods is thoroughly investigated. Aim: The purpose of this practical is to use the glass-bead and caliper techniques to measure the cranial capacity of hominid skulls, and compare the two sets of results obtained in an attempt to determine their concord, and therefore their accuracy. Materials and Methods: The Glass Bead Technique: †¢ Measuring Cylinder †¢ Glass Beads (or items of similar size such as mustard seed or lead shot) †¢ Funnel †¢ Cotton Wool †¢ The following skull specimens: P. troglodytes (male and female specimens), G. gorilla (male and female specimens), P. pygmaeus (male and female specimens), H. sapiens (male specimen) To begin with, all of the foramina (holes) in the skulls, except for the foramina magnum, were plugged with cotton wool. Next, each skull was placed upside down. A funnel was then inserted into the foramen magnum of each skull and glass beads were poured into the cranial vault. Note that glass beads were used because they are small enough to approximate the viscosity of water, and large enough to prevent them falling through minor cracks in the skulls. When the cranial vault was completely packed with glass beads, they were transferred to a measuring cylinder, and their volume was recorded.