Theory Of Evolution By Natural And Sexual Selection


It is commonly thought today that the theory of evolution originated from Darwin in the

nineteenth century. However, the idea that species mutate over time has been around for a long

time in one form or another. Therefore, by Darwin�s time the idea that species change from one

type into another was by no means new, but was rejected by most because the proponents of

evolution could not come up with a satisfactory mechanism that would explain this change.

The most influential evolutionary theories prior to Darwin were those of Lamarck and

Geoffroy St. Hilaire, developed between 1794 and 1830. Lamarck suggested that species evolve

through the use or disuse of particular organs. In the classic example a giraffe that stretches its

neck slightly to reach higher leaves will gain in neck length, and this small gain would be passed

on to its offspring. Geoffroy, on the other hand suggested that the change was discontinuous,

large in magnitude, and occurred at the production of offspring. However, these theories of

evolution were based on a priori explanations that offered no demonstrated mechanism.

Darwin�s theory of evolution differs in that it is based on three easily verified observations.

�First, individuals within a species vary from one another in morphology, physiology, and

behavior. Second, variation is in some part heritable so that variant forms have offspring that

resemble them. Third, different variants leave different number of offspring�. Darwin than

proceeded to elaborate on the mechanism of evolution by suggesting that in the universal struggle

for life, nature �selects� those individuals who are best suited (fittest) for the struggle, and these

individuals in turn reproduce more than those who are less fit, thus changing the composition of

the population. In addition to natural selection, Darwin also suggested that species also evolve

through the complementary process of sexual selection. According to Darwin, in sexual selection,
one gender of a species develops a preference for individuals of the other gender who possess

certain features. The individuals who possess these features will than have a reproductive

advantage over others, resulting in a greater number of offspring, and thus, again, a change in the

composition of the population. Therefore, it was Darwin who made the theory of evolution

feasible by providing the mechanisms of natural and sexual selection.

Darwin�s Formative Years

Charles Darwin was born in England in 1809 and belonged to a wealthy and respectable

family. His grandfather, Erasamus Darwin, was a noted botanical expert in his day who published

two important books, Zoonomia, and the Botanic Garden. In these books, Erasamus speculated

about various evolutionary ideas that were dismissed as too radical (i.e., the nose of the swine has

become hard for the purpose of turning up the soil in search of insects and roots). Darwin who in

his youth read his grandfather�s books with admiration, later commented that his grandfather

�anticipated the views and erroneous grounds of opinion� of Lamarck. Nevertheless, Erasamus

may have unconsciously influenced Darwin in preparing the way for evolution by natural


In 1818, at the age of 9, Darwin entered the Shrewsbury school, which was ran by Dr. Butler.

Darwin later recalled that �nothing could have been worse for the development of my mind than

Dr. Butler�s school, as it was strictly classical, nothing else being taught , except a little ancient

geography and history. The school as a means of education to me was simply a blank�. He was

removed from the school in 1825, and was sent to Edinburgh to study medicine. There he studied

for two years before deciding that he didn�t like medicine. But before he left Edinburgh, he was

introduced for the first time to the theories of Lamarck. According to Darwin at the time he was

not very impressed with Lamarck�s ideas. In 1828, at his father�s suggestion, Darwin entered

Christ�s College in Cambridge to become a clergyman. To Darwin a good education meant

instruction in the methods and logic of thought. Therefore, Just about the only thing he enjoyed

studying there was Paley�s works on theology, because of their logic. For the rest, however, he

judged Cambridge to be just as much a waste of time as Edinburgh and Shrewsbury.

Nevertheless, in his spare time at