Evolution of Man

Scientists continue to debate the history of man. It is generally agreed upon by the scientific community, however, that humans evolved from lesser beings, and this essay will function to provide evidence to support this claim. Several points will be outlined, including the general physical changes that occurred between several key species on the phylogeny of man, and a discussion of dating methods used to pinpoint the age of the fossils. This essay will begin with a brief discussion of dating techniques. In the study of hominid evolution, two main methods of dating are used: carbon-14 and potassium-argon dating. Carbon-14 dating involves the decay of radioactive C-14, which has a half life of 5770 years. This makes this method useful for dating of recent fossils, with good accuracy, up to 50,000 years back. After 5770 years, half of the carbon-14 in a fossil decays to nitrogen-14. Since the ratio of carbon-12 to carbon-14 in a living organism remains the same as in the environment around them because the organism constantly eats and replenishes it, if it were to die, the ratio would change greatly after many years. It is the difference between this ratio now and the time is died that allows a date for it to be established. Potassium-argon dating, another dating method, is possible due to volcanic ash and rocks found near many fossil sites. Rocks and ash created in this manner contain potassium-40, but no argon. As time passes, the potassium-40 decays into argon-40. In the laboratory, the sample is reheated, and since argon-40 is a gas, it is released. The ratio of argon-40 released to potassium-40 still present allows for a date to be assigned to objects near the sample. However, due to potassium's high half-life (1.3 billion years), it is only useful as a dating technique for finds older than 500,000 years old. Also, it is only useful where volcanic activity existed. Both these methods have error margins, ranging from a few thousand years in carbon-14 dating to tens of thousands of years, or more, for potassium-argon dating. However, thanks to scientific breakthroughs, these two processes can be used with reasonable security in establishing a time for fossils.

Humans have existed on the Earth for approximately 3.4 million years. At least, that's from when the oldest human ancestors have been found. The oldest known human is the fossil "Lucy," an Australopithecus, discovered by Donald Johnson and M. Taieb. Australopithecines looked more like primates than modern-day Homo Sapiens; they walked semi-upright, they had low, sloping foreheads, protruding jaws, almost no facial expressions, thick body hair, and were about three feet tall. Over three and a half million years, humans have evolved greatly. We have grown from 3 to almost 6 feet, lost most of our body hair, become slender and adapted to walking, and grown brains over three times as large as the first Australopithecines.

Besides all this, humans (Homo Sapiens) have developed an advanced material culture. Now, instead of living in trees and digging food from the ground with sticks, we live in vast cities of millions and buy our food from the local grocery store with money (another recent development). Humans have come a long way, from Australopithecus to Homo Sapiens. But we are also like the primates in many ways, too. We have the same basic body structure. Their hands are essentially just like ours, except that they don't have opposable thumbs. Their feet are similar to ours, only with longer toes for gripping. And our faces are very similar as well. Nevertheless, we still have come a long way from living in trees to living in cities. Slowly, through hundreds of thousands of years, we mutated time and time again, natural selection ensuring that no harmful mutations continued. From the slow process of evolution, four distinct species emerged and died out, each giving way to its successor: Homo Habilis, Homo Erectus, Homo sapiens Neanderthalesis, and finally, Homo sapiens Sapiens. We've come a long way over our brief (3.4 million years) existence on Earth. The first major step leading to Homo sapiens Sapiens was walking upright, or becoming bipedal. The Australopithecines were the first to do this, albeit rather clumsily. Their gait was, judging by their bone structure, was unsteady at best, and they probably mainly were quadrupedal (walking on all fours). They also retained the ability to climb trees. The oldest Australopithecus fossil is Lucy, an Australopithecus Afarensis. Over 40% of her skeleton was found intact, making Lucy one of the most complete Australopithecus finds as well as the oldest.

The Australopithecines had a brain about the size of an orange (400-550cc), prominent cheekbones, and heavily enameled molars. They were about three feet tall, and had small, underdeveloped thumbs. Their toes were also somewhat shorter than other primates. Australopithecines, while definitely possessing some human characteristics, were still much closer to the chimps and gorillas that we evolved from, so it is safe to assume that they lived similar lives to other primates. They probably, judging from arrangements of fossils at sites, lived in one place in small groups. It is assumed that, like gorillas, one male dominated a group of Australopithecines. We assume this because of their sexual dimorphism. Sexual dimorphism is a noticeable difference in the sizes of males and females in a species. It is usually the males who are larger; in the case of Australopithecines, the males were larger. We know they lived in groups because fossil groups of Australopithecines are often found with more than 5 individuals in the same place. One site had 13 dead in the same place. While Australopithecines are most likely direct ancestors of modern-day humans, they were still relatively unintelligent. Their tools, if any, were limited to sticks and rocks found on the ground. Australopithecines were vegetarians; even if they knew that animals were edible, they still had no reliable means of killing animals for food. That came with the evolution of Homo Habilis. About 2 million years ago, highly evolved Australopithecines made the fundamental realization that then can influence their environment; they made the first tools, began exploiting resources, and made the shift to Homo Habilis at the same time. Homo Habilis is the earliest known member of the Homo genus, and has been found only in Africa. Besides a brain size 50% larger than Australopithecus, Homo Habilis was taller, had an almost hairless face, and flatter nostrils. They were taller than Australopithecines, and were becoming omnivorous. Homo Habilis had, among other things, discovered that meat was edible. They began scavenging dead meat, and added it to their normal vegetarian diets. We know this because of their teeth. Homo Habilis had grown large incisors, just right for tearing chunks of meat. They