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In the Beginning The theory of evolution, formalized by Charles Darwin, is as much theory as is the theory of gravity, or the theory of relativity. Evolutionary theory is a scientific theory dealing with scientific data, not a system of metaphysical beliefs or a religion (Wilkins). Biological theories, and especially evolution, unlike the theories of physics, have been argued long and hard in social and political arenas. Even today, evolution is often not taught in primary schools.
However, evolution is the binding force of all biological research. It is the unifying theme. Living organisms evolve through genetic changes over generations, and planets evolve through the processes of erosion and deposition. In paleontology, evolution gives workers a powerful way to organize the remains of past life forms, and better understand the one history of life. The history of thought about evolution in general, and paleontological contributions specifically, are often useful to the scientists of today. Science, like any iterative process, draws heavily from its history.
We live on an ancient planet. In the Western world, however, people have long believed that Earth had a relatively recent beginning. In 1650, James User, estimating from his close study of the Bible, calculated that Earth was created in 4004 B. C. (Feder 12). Although not everyone agreed with his calculations, until the nineteenth century most people in the Western world shared Bishop Users view that Earth was relatively young and that its entire history was chronicled in ancient texts. During the nineteenth century, geologists and biologists accumulated evidence that Earth was much older than previously suspected.
Their evidence for an ancient Earth came primarily from the fossilized remains of organisms found in sedimentary rocks. The geologists guiding concepts were simple: Rocks form slowly by piling up of sediments, and younger rocks are deposited on top of older ones. A great canyon carved into sedimentary rocks may have a visible record of more than a billion years (Levin 4). Preserved within some rocks were fossils the remains of organisms that lived while the sediments were accumulating. When older rocks are compared with younger ones, slight but significant differences can be observed among similar fossil organisms. The most famous example is fossil horses.
The animals show an increase in size and a reduction of side toes an increase in the height and complexity of teeth, and a deepening and lengthening of the skull (Levin 318). One of the triumphs of modern science has been the development of methods to date materials formed in the past. The discovery that unstable forms of familiar elements, such as carbon, decay at constant rates made it possible to date organic materials. The earliest known fossils have been dated, using the radiocarbon method, as being 3. 8 billion years old. This information, combined with data from the powerful telescopes used by astronomers and physicists, gives strong evidence that our planet is approaching its four-billionth anniversary.
We may never know the exact age of our planet to the day, or even to a specific year because our current methods are not precise, but the plethora of scientific evidence casts doubt on the theory of a six thousand year old planet. Evolution of a species proceeds through gradual changes in populations, not by the production of dramatically different individuals. The relationship of one species to another is determined by similar morphology, nutritional needs, and the amount of DNA they have in common. When a population of species is separated into two or more groups, they will mutate and evolve independently, eventually becoming separate species. A species is defined as a group of individuals who can mate and produce viable offspring (Purves 205). There can be mating between species, but these unions produce infertile offspring.
A horse and a donkey are different species. They can mate and produce offspring, and we call those offspring mules. Mules however, cannot mate and produce more mules because they are infertile. Genetic engineering has also been used to mate otherwise incompatible organisms. Seedless oranges, grapes, and bananas were created by crossing similar but unrelated plants.
Humans impose this kind of artificial selection to create desired characteristics in plants and animals. Natural selection, as observed by Charles Darwin, is an agent of evolutionary change as well. The early horse was accustomed to eating the leaves of trees and shrubs. Paleontolgic evidence shows that grass was spreading across the continent where these fossils were found. Grass is a harsh food for plant eating animals. The leaves contain silica, which quickly erodes enamel from teeth.
Horses that had high-crowned teeth (due to a random mutation of genetic material) were better able to cope with the problem of tooth wear from eating grasses. These horses were likely to have been well nourished and hence lived longer lives and were able to produce more offspring. Those individuals whose inherited characteristics fit them best to their environment are likely to leave more offspring than less fit individuals. In Darwin's own words, Can we doubt that individuals having any advantage, however slight, over others, would have the best chance of surviving and of procreating their kind? On the other hand, we may feel sure that any variation in the least degree injurious would be rigidly destroyed. This preservation of favorable variations, I call Natural Selection (73).
Although evolution is a general theory of the development of life, scientists are still testing many specific hypotheses that seek to explain particular aspects of how evolution operates. With time and fortuity, we may soon know every branch on the tree of life and our common ancestor that was the seed. Works Cited Darwin, Charles. On the Origin of Species by Means of Natural Selection.
London, 1859 Purves, William. Life: The Science of Biology. 5 th ed. Boston 1998 Levin, Harold. The Earth Through Time. 6 th ed. New York 1999 Feder, Kenneth. Human Antiquity. 3 rd ed.
London 1997 Wilkins, John. Evolution and Philosophy 1997. April 8, 2000
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