Evolution 101 Essay, Research Paper

Evolution is the process by which living organisms originated on earth and have changed their forms to adapt to the changing environment. The earliest known fossil organisms are the single-celled forms which resemble modern day bacteria. These single-celled organisms date back about 3.4 billion years. Evolution has resulted in successive radiations of new types of organisms, some of which have become extinct, but most of which have developed into the present makeup of the present world (Wilson, 17).

Evolution has been studied for nearly two centuries. One of the earliest evolutionists was Jean Baptiste de Lamarck. He argued that the patterns of resemblance found in various creatures arose through evolutionary reformations of a common ancestry. Naturalists had already established that different animals become adapted to different styles of life and environmental conditions. Lamarck believed that environmental changes evoked in individual animals and that direct adaptive responses could be passed onto their offspring as inheritable traits. Unfortunately, this generalized hypothesis of evolution by acquired characteristics was not tested scientifically during Lamarck’s lifetime.

A successful explanation of evolutionary processes however was later proposed by Charles Darwin. His most well-known book, “The Origin of Species” by Means of Natural Selection, is a turning point in human understanding of nature and evolution. Claiming diversity within species, Darwin mentioned that while offspring inherit a resemblance to their parents, they’re not identical to them. Furthermore, he noted that some of the contrasts between offsprings and parents were not due entirely to the environment, but were often inherited. Animal breeders were often capable to change the characteristics of domestic animals by selecting those individuals with the most desirable qualities for reproduction. Darwin reasoned that, in nature, individuals with qualities that made them adjust to their environments better, or gave them higher reproductive capacities would tend to leave more offspring; such individuals were said to have higher fitness. Because more individuals are born than survive, a natural selection-should occur, leading to a population that is well adapted to the environment it inhabits. This is also recognized as survival of the fittest. When environmental conditions change, populations require new characteristics to maintain their fitness. Either the survival of a sufficient number of individuals with agreeable traits leads to an eventual adaptation of the population as a whole, or the population becomes extinct. Evolution continues by the natural selection of well-adapted individuals over a stretch of many generations, according to Darwin’s theory(Microsoft 96).

Darwin’s theory however became difficult to test scientifically from a lack of knowledge about heredity itself. When the earlier genetic works of Gregor Mendel came to light, the primary rules of inheritance became known to science during the turn of the century. Mendel had discovered that characteristics are transmitted across generations in distinct units. It was then that the discovery was made that inheritable changes in genes could occur spontaneously and sporadically without regard to the environment. These changes are known as mutations. Since mutations were seen to be the only source of genetic alteration, many geneticists believed that evolution was motivated on by the random buildup of beneficial mutation changes. At the same time as Darwin, the leading evolutionary theory, the science of population genetics was being founded by Sewall Wright, and several other geneticists. They formed arguments to reveal that even when a mutation that is immediately favored appears, that its subsequent spread within a population depends on such variables as: the size of the population, length of generations within that population, the degree to which the mutation is favorable within those individuals, and the rate at which the same mutation will reappear in future descendants. Moreover, a given gene is favorable only under certain environmental conditions. If conditions alter, then the gene may be favored only in an isolated part of the population; if conditions change over time, the gene may become ordinarily unfavorable.

Because different individuals usually have different assortments of genes, the total number of genes available for inheritance by the following generation is usually quite massive, therefore forming an extensive collection of genetic variability also known as the gene pool. Sexual reproduction ensures that these genes are rearranged in each generation. This process is called recombination. Mutations provide the gene pool with an endless supply of new genes; through the process of natural selection the gene frequencies change so that useful genes occur in greater proportions (Ardrey 24).

As the new evolutionary theory came about, it became known as the synthetic theory. Three American scientists made contributions that were particularly influential. Ernst Mayr, a zoologist, showed that new species usually occur in geographic isolation, often following a genetic turn that quickly changes the contents of their gene pools. George Simpson, a paleontologist, proved that using the fossil record, rates and modes of evolution are correlated. A botanist, by the name of Ledyard Stebbins, showed that plants display evolutionary patterns similar to those of animals. Most importantly, this showed that plant evolution has established diverse adaptive responses to environmental pressures and opportunities. These biologists used a extended range of genetic, ecological, and systematic data to show that the synthetic theory was strongly supported by observation and experiment, assisting it to become widely accepted. During the formation of the synthetic theory of evolution, the science of heredity underwent another drastic change.

In 1953 James Watson and Francis Crick demonstrated that genetic material is composed of two nucleic acids, deoxyribonucleic acid (DNA) and ribonucleic acid (RNA). Nucleic acid molecules contain genetic codes that govern the manufacturing of proteins, and direct the biochemical pathways of development and metabolism in an organism. Natural selection thus helps to favor or suppress, if necessary, a particular gene according to how strongly its protein product contributes to the reproductive success of a certain organism.

Life originated more than 3.4 billion years ago, when the earth’s environment was much different from that of today. Especially significant, was the lack of considerable amounts of free oxygen in the atmosphere. Experiments have shown that rather complicated organic molecules, including amino acids, which arose spontaneously under conditions that are believed to have simulated the earth’s environment. The earliest organisms that still exist now would be cells resembling modern bacteria. These simple procaryotic forms were at first anaerobic, but later diversified into and array of adaptive types from which blue-green algae descended. Eukaryotic cells may have evolved through the combination of a number of distinct simple cell types. In order for complex animal communities to develop and survive, plants must first become established to support herbivore populations, which in turn will support carnivores and scavengers.

Plant life on land first appeared about 400 million years ago. Two hundred and Sixty Five years later dinosaurs and mammals came to share the land with them. Although the dinosaurs seemed more adapt, the mammals survived the wave of extinction that eliminated these giants about 65 million years ago. Perhaps these mammals were a bit more “fit.” Humans belong to an order of mammals, the primates, which existed before the dinosaurs became extinct, and still lived on after the dinosaurs were long gone. These early primates seem to have been tree dwelling. Many of the primate attributes, the short face, overlapping visual fields, grasping hands, large brains, and even alertness and curiosity, must have been acquired as needed adaptations. However, once out of the trees and onto the land, development of many of the unique features of the human primate, including erect posture and reduced canine teeth came to be(Schwartz, 1987).

The history of life as inferred from the fossil record displays a wide variety of trends and patterns. Lineages may evolve slowly at one time and rapidly at another time, they may follow one pathway of change for sometime only to switch to another pathway, and they may diversify rapidly at one time and then contract during another. The key to many of these patterns is the rate and nature of environmental change. Species become adapted to the environmental conditions that exist at a given time, and when change leads to new conditions, they must evolve new adaptations or become extinct. The extinction occurs when the environment undergoes a particularly rapid or extensive change. These are followed by waves of development of new species. The times of mass extinction are not yet well understood. Although the most famous extinction event is that of the dinosaurs, about 65 million years ago. Such events appear in the fossil record as far back as Precambrian time when it is believed that life first began. Ideas of mass extinction has been an issue of controversy between many geologists towards the idea that it is related to intermittent catastrophes such as the striking of the earth’s surface by a large asteroid or comet. Many paleontologists and evolutionary theorists reject such ideas and believe them to be unjustified. They feel that periods of mass extinctions can be accounted for by fewer spectacular evolutionary processes and by more earthbound events such as cycles of climatic change and volcanic activity, even perhaps a melting of the polar ice caps, causing another ice age, as we have seen in the past.

Whatever proposals may eventually prove to be true, it seems fairly certain that periodic waves of mass extinction do occur, and can very likely occur again. Species adapted to live in environments that are changeable in the short term have broad tolerances, which may better enable them to survive when extensive changes occur. Human beings are uniquely adapted in that they make and use tools and devices and invent procedures that give them extended control over their environments, such as medicine. Humans are also responsible for notably changing the environment itself. The effects are very perplexing, and misunderstood by all geologists alike and cannot be predicted, and yet the eventuality is that evolutionary patterns in the future will reflect the influence of the human species of today(Microsoft96).