History of Evolution....

It is hard to say at what time before the nineteenth century that the idea of evolution in the animal kingdom was first raised. Several Greek philosophers thought that the living world was subject to transformations. Their conclusions were based on philosophical ideas and speculations.


In 1801, the French naturalist Lamarck became the first to introduce the concept of evolution. He published his work in a book called Zoological Philosophy. Cuvier, another French naturalist published History of Fossilized Bones" in 1812, in which he compared present day animals with fossils showing the existence of extinct species.


Charles Darwin (1809-1882), British naturalist, laid the foundation of the evolutionary theory with his concept of the development of all forms of life through the slow-working process of natural selection. After graduating from Cambridge in 1831, the 22-year-old Darwin was taken aboard the English survey ship H.M.S. Beagle.


He noted, for example, that certain fossils of supposedly extinct species closely resembled living species in the same geographical area. In the Galapagos Islands in Ecuador, west of South America at the equator, he studied some forms of life such as huge turtles and swimming lizards not found anywhere else in the world. Darwin saw that these animals were similar to more common forms. The similarities convinced him that the Galapagos animals were related to more common turtles and lizards. In Galapagos, Darwin saw finches that shared so many features, but differed mainly in their beak structures, eating habits, and their sizes. He thought they must have had a common ancestor. Each of the 13 famous finches of Galapagos was identified as a distinct species.


After returning to England in 1836, Darwin began recording his ideas about changeability of species in his Notebooks on the Transmutation of Species. Darwin's explanation for how organisms evolved was brought into sharp focus after he read An Essay on the Principle of Population (1798), by the British economist Thomas Robert Malthus, who explained how human populations remain in balance. Malthus argued that any increase in the availability of food for basic human survival could not match the large rate of population growth. The latter, therefore, had to be checked by natural limitations such as famine and disease, or by social actions such as war.



Malthus introduced the term "Natural Selection" that Darwin popularized. Darwin immediately applied Malthus's argument to animals and plants, and by 1838 he had arrived at a sketch of a theory of evolution through natural selection. For the next two decades he worked on his theory and other natural history projects.
Darwin's theory was first announced in 1858. In a paper presented at the same time by Alfred Russell Wallace, a young naturalist had come independently to the theory of natural selection. Darwin's complete theory was published in 1859, in The Origin of Species. Often referred to as the "book that shook the world," the book was sold out on the first day of publication and subsequently went through six editions.


Darwin's theory of evolution by natural selection is essentially that, because of the food-supply problem described by Malthus, the young born to any species intensely compete for survival. Those young that survive to produce the next generation tend to embody favorable natural variations (however slight the advantage may be) and these variations are passed on by heredity. Therefore, each generation will improve adaptively over the preceding generations and this gradual and continuous process is the source of the evolution of species. Natural selection is only part of Darwin's conceptual scheme; he also introduced the concept that all related organisms are descended from common ancestors in his second book, Descent of Man (1871).


In The Origin of Species, Darwin did not offer solid evidences of human evolution, only suggesting in the conclusion that in the future, "Much light will be thrown on the origin of man and his history." In the same book, Darwin described serious challenges to the whole concept of natural selection in three chapters with the following titles:
•         Difficulties of the theory, chapter 6.
•         Miscellaneous objection to the theory of natural selection, chapter 7.
•         On the imperfection of the geological record, chapter 10.


In his second book, Darwin presented his guesswork about humans and apes. He believed that humans were the products of biological evolution, and that they descended from primitive ancestors. His hypothesis did not state that humans descended from any of the great apes: orangutan, gibbon, chimpanzee, and gorilla. Both humans and apes descended from some common primate ancestors that are now extinct.


The reaction to The Origin of Species was immediate. Some biologists argued that Darwin could not prove his hypothesis. Others criticized Darwin's concept of variation, arguing that he could not explain the origin of variations. In fact, many scientists continued to express doubts for the following 50 to 80 years. The most publicized attacks on Darwin's ideas, however, came not from scientists but from religious opponents. The thought that living things had evolved by natural processes denied the special creation of humankind and seemed to place humanity on a plane with animals; both of these ideas were serious contradictions to orthodox theological opinion.