Charles Darwin was an English naturalist who was fascinated with nature. In 1831 he began a five year voyage on H.M.S. Beagle. It was a British navy mapping expedition but Darwin had ample opportunity to explore, observe, study and record the natural world. The Beagle sailed to south America and the Galápagos islands. Darwin eventually returned to England with his mind and notebooks filled with fantastic images and detailed recordings.

Charles
Darwin

The prevailing explanation of the enormous diversity of life in that period was the literal interpretation of Earth's creation as described in Genesis, the first book of the Bible. God created each individulal species of animals and plants about six thousand years ago, in what was essentially an instanteanous creation. And these species remained fixed and unchanged.

But for many scientists the origin of species was the 'mystery of mysteries' at that time. Darwin wanted to solve this mystery. So he addressed the main issues of biology such as the great diversity of organisms, their origins, relationships, similarities, differences, their geographical distribution and their adaptions to the surrounding environment. And his ideas became a cornerstone of modern biology.

H.M.S. Beagle

However, Darwin had to develop his ideas in private. He was reluctant to issue his theories, eventhough from the evidence he had gathered and the observations he had made he knew that living things are related and have changed over millions of years. But he knew his theories on evolution and natural selection went against established social and political order. Undermining scripture was not a popular thing to do. To confront the united establishment of science, politics and the church would get him into serious trouble. He could be charged with blasphemy or heresy, a serious charge in those times. His career and reputation could be destroyed even though he was a respected and well known scientist in his day.

Since many of his scientific peers believed that God created all animal and plant life, and these species remained unchanged since their creation, he repeatedly delayed publishing his ideas. He dreaded the controversy they would generate. But in 1859, after many many years of work he had the courage to go against the dominant belief of those days and he fundamentally changed the future of not only scientific thought, but also religious and theological thought.

Darwin. and many others, were aware that the fossil record revealed a history of change. His genius was to suggest a robust and plausible mechanisn by which such changes could come about. So in 1859 Darwin's book, Origin of Species by Means of Natural Selection, was published. A truly revolutionary idea from a revolutionary scientific thinker. His theory is one of the greatest contributions of our understanding of Science and life itself and serves as a foundation of the biological understanding of the natural world.

After publication in 1859, bitter controversy ensued. Darwin and his book were despised by many respected members of the church and scientific community. It dealt a massive upset to the biblical account of creation as well as against the assumption of the unique status of Man. However, there was a general acceptance of Darwin's ideas amongst the younger generations of scientists. And as they began to embrace his ideas and accumulation of fossil records intensified, the public became more prepared for the acceptance of earlier human species and of a world much older than 6000 years.

The Theory of Natural Selection

Darwin's observations were to contradict the 'Genesis' version of the creation of life. They led him to the conclusion that all species derived from a common ancestor through the process of natural selection. He observed that in any population of species, individuals are all slightly different from one another.

Individuals with a trait more suited to the environment are better able to survive and reproduce. These individuals are the ones that pass on these traits more frequently to the next generation.

Subsequently, their traits become more common in their descendents and in the population as a whole. So, over time, organisms better suited to the new environment will thrive. Organisms not ideally suited would become extinct. Given enough time a species may change enough traits to eventually become a totally different species.

But to go back to Darwin and natural selection. Darwin called this "descent with modification."

Natural selection is considered to be the main process, or the engine, driving evolution. It should not be regarded as a process just to weed out or kill off less suited individuals in the environment. Its consequences result in the enormous diversity of genomes, species and complex life forms we see around us today. The process is slow and relies entirely on variations in the genes of an organism resulting from random mutations. Variations do not arise because they are needed. It is an entirely random process governed by the laws of genetics.

The basic concept of evolution had been around the Scientific community before Darwin's time. However, until Darwin came along, it lacked any plausible mechanism to support it. Darwin realised that in a world with varied environments, as well as having a history of changing environments, different traits would be favourable in different environments. Individuals would evolve to suit their environment. They would occupy an ecological niche increasing their survival chances.

In summary, we can say the following about Natural Selection;

• The goal of life is to survive and reproduce, thereby passing on genetic information to the next generation. Many organisms tend to produce more offspring than the environment can support


• Resources such as food supply for individuals is key to survival. Lack of resources means increased competition between individuals which results in a struggle for existence and pressure on the population size of the individuals. Some individuals will not survive.


• The individual who die as a consequence of this competition were not totally random. Darwin found that those individuals more suited to their environment were more likely to survive.


• This resulted in the well known phrase survival of the fittest, where the organisms most suited to their environment have greater success in the struggle for existance


• Those individuals who are better suited to their environment exhibit desirable characteristics Through the process of reproduction will contribute disproportionately more to the offspring that make up the next generation


• So the population of the next generation will be disproportionate. It will consist of a higher proportion of individuals that possess whatever traits enabled their parents to survive and reproduce. These favourable traits will tend to accumulate in the population.

It should be noted that for natural selection to occur and a population to evolve, two requirements are essential:

• There must be a heritable variation for some trait such as beak size for birds


• There must be differential survival and reproduction associated with the possession of that trait, that is a difference in reproductive rate from one generation to the next. So a greater reproductive rate due to a particular trait within a species will not lead to evolution if this trait is not heritable