Thoeries of Evolution
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 resembling modern bacteria; they date from about 3.4 billion years ago. Evolution has resulted in successive radiations of new types of organisms, many of which have become extinct, but some of which have developed into the present fauna and flora of the world (Wilson 17).
Evolution has been studied for nearly two centuries. One of the earliest evolutionists was Jean Baptiste de Lamarck, who argued that the patterns of resemblance found in various creatures arose through evolutionary modifications of a common lineage. Naturalists had already established that different animals are adapted to different modes of life and environmental conditions; Lamarck believed that environmental changes evoked in individual animals direct adaptive responses that could be passed on to their offspring as inheritable traits.
This generalized hypothesis of evolution by acquired characteristics was not tested scientifically during Lamarck's lifetime.
A successful explanation of evolutionary processes was proposed by Charles Darwin. His most famous book, On the Origin of Species by Means of Natural Selection (1859), is a landmark in human understanding of nature. Pointing to variability within species, Darwin observed that while offspring inherit a resemblance to their parents, they are not identical to them. He further noted that some of the differences between offspring and parents were not due soley to the environment but were themselves often inheritable. Animal breeders were often able to change the characteristics of domestic animals by selecting for reproduction those individuals with the most desirable qualities. Darwin reasoned that, in nature, individuals with qualities that made them better adjusted to their environments or gave them higher reproductive capacities would tend to...