The evolutionary relationships of Australopithecus and Homo are still argued today among top anthropologists. The direct human phylogeny is not certain, and many links to modern man from four million years ago are possible. What is not argued, however, is that the evolution of man was an evolution from the neck up, rather than from the neck down. After our transition from the arboreal region of Africa to the terrestrial area of the savanna, our physiology below the neck, for the most part, has not changed. As a result, differences among each hominid are not as distinct as some would hope.
In example, the comparison between Australopithecus africanus and Homo erectus can be classified as one of degree, not kind. A. africanus, the southern ape of Africa, inhabited the Africa region around 2. 6 to 2. 0 MYA, while Homo erectus, upright man, encompassed the land around 1. 6 to about 1/2 MYA. Despite over one million years of evolution, the differences between the two hominids is limited, and many physical, behavioral, and natural environment adaptations are shared. Instead, a slow, progressive evolution of man is represented between A. africanus and Homo erectus.
During the mid-nineteenth century, the great scientist Charles Darwin predicted human evolution to be in Eastern Africa. Sure enough, in 1851 a Dutch anatomist named Eugene Dubois discovered the remains of a hominid at the East African Coast that was classified Homo erectus because of its depiction of bipedalism. Other specimens that represented Homo erectus were excavated in Asia, and the Peking Man for a while, was thought to be the oldest descendant of man (Reader 91). This belief held up for a while until Professor Dart found the first fossil of A. africanus at Taung, South Africa in 1924.
This fossil was determined to be about one-million years older than the fossils of Homo erectus. Unlike Homo erectus, however, A. africanus did not move out of Africa. It was only conditioned to survive in the savanna of Southern Africa. On the other hand, remains of Homo erectus have been found in areas of the Old World such as Java, China, Near East, and Northern Africa. How is it that Homo erectus was able to survive the harsh glacier climate of Asia? This question can be answered by examining the physical and behavioral adaptations, most similar but a few important differences, that each hominid endured during its escapade on earth.
Even with approximately one million years of evolution, some adaptive physical characteristics between A. africanus and Homo erectus remain the same. There is no projection of bone where the chin would be in either hominid. The brain in both hominids is behind the face and each lack a forehead. This similar characteristic exemplifies the fact that the evolution of man from the neck up was an extremely slow process.
In the A. africanus, a clear tendency to the reduction of the jugate (paired) teeth and the growth of the front teeth show that A. ricanus could move its jaw not only up and down like a chimpanzee, but now sideways for better chewing purposes. The evenness of the canines with the tooth row in both A. africanus and Homo erectus indicate an omnivorous diet (Guilaine 34). In the movie Mysteries of Manhood by National Geographic, an electron microscope of tooth wear from an A. africanus compared to tooth wear of A. robustus, shows that the A. africanus must of ate soft foods, again indicating an omnivorous diet. Another physical characteristic that appears the same in both hominids is sexual dimorphism.
Although not as discrete as in apes and baboons, the difference in relative size between males and females remains definitive in A. africanus and Homo erectus. Finally, the most important similarity between the two hominids is their use of bipedalism in locomotion. The single most important distinction between ape and man is the characterization of bipedalism. During the transition from the arboreal region to the savanna, the ability to walk on two legs became essential. The idea of natural selection can be illustrated during the transition to bipedalism.
For example, physically, there was a change in balance where now the head must be above the spinal cord. Those certain hominids that possessed the genes for a better balance with the head and the spinal cord most likely lived longer and had a better chance of reproducing more offspring. Behaviorally, bipedalism provided hominids with a greater ability to manipulate the world around them. Field of vision was improved because of an upright position. Also, now hands were free to handle tools or even carry food from place to place. Undoubtedly, the first evolutionary change that man underwent was the transition to bipedalism.
The different adaptive physical characteristics range small, mostly due to the anatomy of hominids, that was already established. Height difference between the hominids is largely noticeable. The A. africanus was approximately four feet tall while a finding in Kenya by Richard Leakey of a twelve year old male suggested that this Homo erectus would grow to be about six feet tall. The height difference could be the result of many reasons. One, the diet among hominids was continuously becoming more concentrated in protein as the transition from an herbivorous to a more omnivorous diet was occurring.
Secondly, height was probably better for protection because the appearance to predators would be more intimidating. Thirdly, as Homo erectus moved out of Africa and into colder regions, the larger body size would be better suited for the conservation of heat (Wenke 88). Lastly, because the brain case was slowly increasing, a larger body was needed to hold up and balance the head. Also different between A. africanus and Homo erectus is that A. africanus showed no large eye brow ridge while Homo erectus, on the other hand, did show a large eye brow ridge.
Another difference can be seen in the reduction of the molars in Homo erectus from A. africanus. This is the cause of diet, and the more consumption of softer foods did not bring on the necessity for large molars. However, this difference is very slim and the mouths of both A. africanus and Homo erectus still remained ape-like. Finally, the most important difference physically between the two hominids was the size of the brain. The brain size of Homo erectus is significantly larger implying behavioral and social improvements within the group.
Culture is a major adaptive mechanism, and the shift in adaptive behavioral characteristics between the two hominids is a strong reason why one hominid is referred to as Australopithecus and the other Homo. Both hominids must have been social or their survival alone in the harsh savanna would be almost impossible. A. africanus, with its frail body had no way of defending itself against larger predators. To survive, A. africanus used the family structure for protection as well as intelligence. Food sharing among social groups most likely occurred in both A. africanus and Homo erectus.
This resulted in a constant improvement among kin within the social group. Although both groups of hominids were social, the more complex social relations among Homo erectus is a major distinguishing factor. Gestural and verbal communications were more complex with Homo erectus, because their brain capacity was increasing (Watson 77). More importantly, the use of fire is first seen with Homo erectus. This ability to manipulate fire allowed for many improving adaptations for man. They were now able to leave Africa and endure the colder regions of Asia. Fire softens food and can also hoard off predators.
Another importance is that fire lengthens the day and allows for more social interaction within the group. The longer the group is interacting, the more learning and exchanging of ideas is occurring. One other distinct difference between A. africanus and Homo erectus is the use of tools. For the first time, the definitive use of manipulated tools is seen with Homo erectus, not seen before with any other hominid. Although both A. africanus and Homo erectus used the technique of hunting and gathering, it is with Homo erectus where we find a true hunter that has specific uses of tools.
It is likely possible that A. africanus used simple tools such as a chimpanzee does with sticks and other objects to obtain food. However, the Homo erectus hunter had manipulated core tools referred to as Oldowan tools. Homo erectus was not yet sophisticated enough to take the flakes from the core stones and manipulate them into other tools for use, but still, the core tools were a giant leap for this hominid. The Acheulian hand ax is commonly found with the remains of Homo erectus, and the presumption is that these tools were used for chopping and digging.
Clearly, the use of tools for Homo erectus compared to A. africanus, is a major distinguishing factor between the hominids. One must remember that the path to modern man was in no way linear. Many of the hominids that reigned, coexisted. For example, Homo erectus was around during the period when A. robustus also existed. Why is it that we see Homo erectus as part of our human ancestry and not A. africanus? The reason lies in Darwin s theory of natural selection. A. robustus did not adapt to the surrounding environment as well as Homo erectus, and therefore, became an evolutionary dead end.
This theory can also be applied to the comparison of A. africanus and Homo erectus. The evolution of these two hominids can be linked to natural selection. Those individuals who could better adapt to the environment, either with their knowledge of tools or with their knowledge with fire for example, would have a better chance of living longer and passing those genes and knowledge onto their offspring. The slow process of adaptive learning is the real, underlying process of evolution that was exemplified between A. africanus and Homo erectus during the long journey to modern man.