Although other genera contain primate bipeds, the Australopithecine’s are considered to have the most and to contain the ancestor of the homo genus. Which Australopithecine that is the direct ancestor of the genus Homo is not yet clear. Candidates for direct homo ancestry include A. africanus, A. garhi, and Kenyanthrops platyops. Fossils of A. africanus were first discovered in 1924 by a colleague of Raymond Dart in Taung, South Africa. Dart noted the odd apelike characteristics combined with human traits including the base skull hole over the spinal column indicating bipedalism. This Taung Child’s (given her name by location and approximate age of three) fossils compare with the bones of a 9 year old human suggesting the growth rate was more similar to chimpanzees than modern Homo sapien. More recently, in 1999, a new species of genus Australopithecus was discovered in Ethiopia called A. garhi. Much more evidence is needed; however because of dental ratios of front and back teeth, and other dental indicators, it’s believed that A. garhi could represent the missing link between the genera Australopithecus, and Homo. Lastly Kenyanthrops platyops is a genus very closely resembling A. afarensis and in fact fossils may be incorrectly categorized in one or the other. Kenyanthrops has a small brain case, small molars, and a humanlike flat face which lead some to believe this is the direct ancestor to Homo.
Primate bipedalism was an advance which did more than allow the ape to walk upright. Bipedalism provided a platform on which other abilities could ignite. By walking upright evolution created a means to dissipate heat allowing the development of a larger brain. This larger brain, and the possibilities it created such as tool usage, gave rise to the evolution of genus Homo. As already implied, the brain size of genus Homo was remarkably larger than that of their Australopithecine ancestors. Stone tool usage, which began the Lower Paleolithic era (the first part of the Stone Age), dates back 2.6 million years ago. These are found in the same areas, and are dated around the same time, as the first emerging Homo, the H. habilis. The larger brain capacities found in Homo habilis is given credit for the imaginative creation of these tools. Tool usage, bipedalism, and an ever increasing brain size created Homo erectus.
Homo erectus was first discovered in 1887 by a Dutch physician Eugene Dubois. His passion was to find the missing link between humans and ape. After several years of searching he finally found fossilized remains seemingly both ape and human like in characteristics. The femur indicated bipedalism and was human in shape. Its brain size was much larger than apes, but not quite as large as found in modern humans. Dubois classified these skeletal remains as Pithecanthropus erectus, later reclassified as Homo erectus. Notable about the inside of H. erectus’ brain case is the highly developed speech area leading some to believe the possibility of the beginnings of lingual ability. At the very least this is strong evidence of H. erectus’ candidacy of being human ancestors.
The larger brain size in Homo erectus also allowed for a more advanced culture and learning than its predecessor. They created hand axe tools from flint which took into account the raw nature of the stone rather than preconceived patterns which proved less efficient and more costly in terms of resources. Their ability to think in this way is a tribute to their evolved mind. Homo erectus also used fire for protection and possibly even for warmth and cooking near the later stages of their evolution. Another tribute to H. erectus’ ability to think is their ability to organize and hunt for large animals. This ability is suggested from the remains of a 400,000 year old site in Spain, and at another site were animals were thrown into a swamp dismembered. At this later mentioned site, we have eliminated the possibility of natural disaster, and the amount of other large predators was negligible, and therefore it is believed H. erectus is responsible.
Fossil remains dated between 0.4 and 0.2 million years ago show a transitional phase between H. erectus, to H. sapien. The fossils indicate larger brain sized, and a mixture of features between the two species. During this transition a new technique evolved for tool making called the Levalloisian technique, a technique that yields a larger cutting edge. Around the same our ancestors began attaching these cutting edges to wooden handles to create knives and spears. Although it’s clear that H. erectus is our direct ancestor, how this transition occurred is debated. Two main theories exist on how H. erectus evolved into H. sapien. The first theory suggests that H. sapiens evolved in individual places simultaneously. Proponents of this theory mark the differences in H. erectus skeletal fossils between different localities, and the similarities of those differences to the diverse human populations of today. The other more recent theory is also supported by genetic evidence that H. sapien evolved from a single population of H. erectus from Africa, and then spread into other continents after the transition. Both theories have their merits.
Now that we have traced the path from Australopithecus to H. sapien, one question remains. Where do the Neanderthals fit in? Neanderthals on average contained a larger brain than modern humans. Some speculate that they were actually an extreme form of archaic H. sapien, and therefore should be classified as a direct ancestor to modern H. sapien. The conclusion to this debate should be very interesting.
The path from Australopithecine to Homo sapien is a fascinating story of geological, environmental, and cultural changes all contributing to our evolution. Had Africa not slammed into Eurasia, we may not (and probably would not) exist today. The conditions conducive for bipedalism may not have occurred, and therefore the bipedal advances making larger brain size possible could have never developed, if this collision did not happen. I wonder what happens in the story of our lineage. What will a civilization a million years from now categorize us as? If only I could leapfrog through time to find out!