SECTION A

Introduction to Evolution

Evolution is the process of change in all forms of life over generations and evolutionary biology is the studey of how evolution occurs. before the 18th century, specification on the origins of organisms rested on mythology and superstitous not on any tetable scientific theory.

Early greek philosopher, notably xenophanes, empedocles and aristotle developed an early idea of evolutionary change. they recognized fossil as evidence of life in the past that they believed had been destroyed by natural catatrophe. despite their intellectial inquiry, the greeks failed to establish an evolutonary concept and the issue declined well before the rise of religion. the opportunity for evolutionary thinking become even more restircted as religious accounts of earth's creation became accepted as a principle of faith.

Lamarck's Theory

French biologist jean baptiste de lamarck (1744-1829) published the first complete explanation of evolution in 1809, the year that charles darwin was born. he made a convincing case those fossils were remains of extinct animals. lamarck proposed a theory; the inheritance of acquired characteristics that stated: organisms, by strivind to meet the demands of their environment,acquire adapations and pass them by hereditary to their offspring.

According to lamarck, the giraffe evoluted its long neck because its ancestors lengthened their necks by stretching to obtain food and then passed the lengthened neck to their offspring. over many generations, these changes accumulated to produce the long neck of modern giraffes. lamarck's concept of evolution is called transformational bacause it claims that as individual organism transform their characteristics through the use and disuse of parts, hereditary makes corresponding adjustment to produce changes(evolution). lamarck theory is now rejected because genetics studies show traits acquired by organism during its lifetime, such as strengthened muscles are not inherited by offspring.

Darwin's Concept

The understanding of evolutionary biology began with the 1859 publications of charles darwin's on the origin of the species by means of natural selection. darwin's evolutionary theory differs from lamarck's in being a variation theory, based on the distribution of genetic variation in populations. evolutionary change is caused by differential survival and reproduction among organisms that in hereditary traits, not by the inheritance of acquired characteristics.

Darwinism

1. perpetual change: this is basic theory of evolution on which the others are based: it stated that the living world is neither constant nor perpetually cycling, but is always changing. organisms undergo transformation across generations throughout time. this theory is vindicated by the presence of fossil records.

2. common descent: the second darwinian theory "common descentz" stated that all forms of life descended from a common ancestors through a branching of lineages. this theory has been supported by studies such as comparative anatomy, cell struture and macromolecular strutures(including those of the genetic material, DNA ) that have shown there is basic similarities among organisms, that resulted iin life's history that has structure of a branching evolutionary tree called a phylogeny.

3. Multiplication of species: darwin's third theory stated that the evolutionary process produces

4. gradualism: gradualism stated thhat the large differences in anatomical traits that characterized diverse species originates through the accumulation of many smalll incrementa changes over very long period of time

5. natural selection: Darwin's most famous theory: rest on four propositions: organisms varies, that is they are not exactly like their parents. these variation are or may be hereditary i.e they may be passed along to descendants,due to the dynamics of reproduction in all species there is a continual struggle for existance in nature. those best adapted to survive in a given environment will be the most likly to survive and should therefore leave the most descendants.