His ideas have had a great impact on a wide array of human endeavours than any scientific advancement of the past 150 years.His research work on evolution provided the first scientific explanation for the diversity of life. His explanation of how evolution works has attracted more controversy than most scientific ideas. This is because it has affected not only science but also philosophy, religion and human attitudes. Charles Robert Darwin (1809-1882) was an English naturalist.
At the age of eight, his interest in observing the natural world was manifested. At that age, he was an enthusiastic but haphazard collector of shells. At ten, his interest shifted to the habits of insects and birds., At fifteen, he preferred hunting, fishing and observing the natural world to doing his schoolwork.
At the university, he could not complete his study of medicine, because that was not his area of interest. He later graduated from Cambridge University as a clergyman but was still interested in natural history.
At the age of 22, one of his professors at Cambridge University, John Henslow arranged for him to take part in a training expedition led by an eminent geologist. Henslow had earlier noticed and respected Darwin’s real interest in natural history. He therefore arranged that he be offered the position of naturalist in the ship they were about to sail in. Do you know that right from the 1770s naturalists had always been posted on all British voyages to distant lands? The aim was to gather more knowledge of nature to add to the store of human knowledge .
The ship they boarded was called H.M.S. Beagle the main aim of the voyage was to complete an earlier work of mapping the coastline of South America. While on the expedition, Darwin had chances to study many diverse forms of life on the islands where they stopped, near mountain ranges and along rivers. He returned to England in 1836, after nearly five years at sea and he began a long life of study and contemplation.
When Darwin came back to England, the question that disturbed him was, ‘What could explain the remarkable diversity among organisms?’ Luckily, field observations he had made during his voyage enabled him later to recognise two clues that pointed to the answer.
First, while the coast of Argentina was being mapped, he repeatedly got off the ship for exploratory trips inland. On these trips, he made detailed field observations and collected fossils. He saw for the first time many unusual species, including an armadillo. Among the fossils were remains of the now extinct Glyptodonts were very large animals that closely glyptodonts. resembled the living armadillos.
Darwin became puzzled and started wondering: If both kinds of animals had been created at the same time, if they lived in the same part of the world, and if they were so much alike, then why were armadillos still moving about while the glyptodonts were long gone and buried? Nothing else in the world resembled either animal. Although nobody including Darwin had ever seen one species evolve into another, he later wondered whether armadillos were descendants of glyptodonts.
Second, he had observed that populations of similar kinds of organisms that lived in different geographic regions often showed remarkable differences in some of their traits (that is, characteristics). For instance, Darwin saw giant land tortoises on the Galapagos Islands which were off the coast of Ecuador. To his surprise, all the tortioses were not identical. It was recorded that even natives of those islands and the sailors could tell which island a particular animal had come from just by looking at it . Darwin reasoned that perhaps all those species descended from the same ancestral form and had become slightly modified after they became isolated on different islands.
Darwin again wondered how such modification could occur. He got a clue from a book published by Thomas Malthus in 1798. The title of the book was ‘Essay on the Armadillo Glyptodont principles of population’. According to Malthus, ‘any population tends to outgrow its resources and its members must compete for what is available’. This statement struck Darwin and he thought about all the populations he had observed during his voyage. He thought about how the individual members of those populations had differences in body size, form, colouring and other traits. It then dawned on him that some traits could lead to differences in the ability to secure scarce resources.
Furher more , Darwin got a clue of how modifications could occur from Thomas Malthus’s ‘Essay on the principles of population’. With that clue, Darwin declared that it was natural selection, that is nature selecting the ‘fit’ and rejecting the ‘unfit’ that led to modifications in members of a species. He described the process of natural selection as follows :
If there were struggles for existence (competition) within a population, then individuals that possess superior physical, behavioural or other attributes might have an edge in surviving and reproducing. In other words, Nature would select individuals with advantageous traits and eliminate others — and so a population could change. Favoured individuals would pass on the useful traits to offspring, their offspring would do the same and so on.
Gradually, descendants of the favoured individuals would make up most of the population, and less favoured individuals might have no descendants at all. Darwin published his work in 1859 and it caused an immediate sensation. Many people were very disturbed because the theory implied that humans probably evolved from apes, monkeys, etc, since all share similar characteristics.
Surprisingly, in 1858, Darwin received an essay from a young English naturalist named Alfred Russel Wallace (1823-1913). The essay was on ‘Theory of evolution by natural selection’! What a coincidence! Both of them had independently reached the same conclusion about evolution.
However, Darwin was given the credit of propounding the theory because of the amount of evidence he marshaled out. Thus, Darwin’s theory of evolution is one of the main unifying themes of the biological sciences. It provides an explanation for three main sets of facts about life on earth, which we observe . These are:
i. The incredible display of different types of living things we see about us.
ii.The different degrees of likeness among the living things. The likeness could be anatomical or molecular.
iii. The fossil record that shows a sequence in the kinds of organisms that have lived on earth over billions of years
