Tool Use and Culture The genus Homo was the first to leave clear evidence of toolmaking. Pebble tools of Homo erectus were described by Louis Leakey, and he named the collection of artifacts "Oldowan" culture, from the Olduvai Gorge where some of his most famous excavations were done. On the basis of his collection of African fossils dated to between one million and two million years ago, Leakey proposed a new species, Homo habilis, which would be intermediate between Homo erectus and Homo sapiens, but there were too few fossils from this critical period to make the sequence clear. In any case, the simple pebble tools of the earliest members of the human genus were gradually supplanted by somewhat more sophisticated implements made by chipping both sides, along with a growing preference for flint over softer stones. There are many more examples of flint tools than there are of actual bones of human ancestors from this period. The techniques used for making these tools were evidently handed down from generation to generation, and the patterns were quite conservative, so tools from a given culture can be identified wherever they are found. The tools and artifacts of the later members of Homo erectus are known as the Acheulian culture. The most characteristic tool of this culture is the hand axe, used for chopping, cutting, scraping, and possibly even as a weapon. The species to which modern humans belong first appeared between 200,000 and 300,000 years ago. In 1856, when the first example of Homo sapiens was discovered, it was named Neanderthal man because the skeleton was found in a cave by the Neander Valley near Dusseldorf, Germany. Neanderthals were a robust species with a somewhat larger brain than modern humans. They wandered widely, leaving their remains over much of Europe, Asia, and Africa. The name Mousterian culture was coined to describe their artifacts, which were much more sophisticated than Acheulian tools. Finally, perhaps as recently as fifty thousand years ago, Neanderthals were replaced by fully modern humans. The two groups can be separated into the subspecies Homo sapiens neanderthalensis and Homo sapiens sapiens. At about the same time the Neanderthals disappeared, the Mousterian artifacts were replaced by much more complex and widely varied implements of the Aurignacian culture. The explosion of cultural innovation-including cave paintings, carvings, and other artistic and technological inventions- had a remarkable effect on life. The first fossils of the sapiens subspecies were found in a limestone cliff atCro-Magnon in southern France in 1868. They and numerous later finds from the same period were given the name Cro- Magnon man, and from the very beginning, they were recognized as being fully modern in form.
How Hydrostatic Skeletons Work Although hydrostatic skeletons operate on the basis of fluid pressure, there are certain constraints as to how this pressure can be generated and on the makeup of the body wall resisting the pressure. First, sets of muscles that will exert the pressure on the body must be located external to the fluid compartment or tissue that will function as the hydrostatic skeleton. Second, there have to be reinforcement fibers arranged in a helical pattern around the hydrostatic tissue or space. If fibers are just arranged in a circular or longitudinal pattern, bending of the structure may cause the creation of kinks or possibly bulges in the wall, due to pressure exerted on the body wall. In both cases, deleterious effects can occur on body organs or an aneurysm may form in the wall that may lead to compromising the structure through its rupture. To prevent such adverse conditions, fibers are arranged in a helix around the body wall. This same type of reinforcement is seen in the construction of the walls of high-pressure hoses. Since the fibers are wound at an angle around the structure, bending does not cause an aneurysm to form and there is no chinking of the wall. This type of fiber arrangement is found in the walls of annelids, nemertines, and flatworms, among others. The fibers are often composed of collagen, a helical protein.
