The father of evolutionary biology, Darwin's contribution to science is significant. Darwin Day is celebrated on February 12 every year.

Survival of the fittest, struggle for existence, and natural selection, these catchphrase come to mind when we think of Darwin. Charles Robert Darwin was one of the most significant individuals in the history of science and is considered as the father of evolutionary biology. He published these revolutionary theories in his book The Origin of Species in 1859. The expedition on the ship HMS Beagle in 1830s to various places around the world gave him a chance to document several aspects of biology, geology and anthropology that resulted in his book Voyages of the Adventure and Beagle (1839). Darwin's ideas were inspired by the experience and observations he had on the famous Beagle Voyage.

He developed his theory of evolution by natural selection through his four observations. His first observation was that all organisms are capable of producing more offspring than are needed to replace their parents. For example, frogs produce hundreds of eggs but all of them do not fertilize, hatch, and become adults. Also, a single tree produces thousands of seeds and all of them do not grow.

Darwin's second observation was that the population of several different species of animals and plants have a tendency to stay fairly constant over long periods of time. For example, herds of many animals live on the plains of Africa such as wildebeest, zebra, gazelles etc. Each year many of the females give birth, but the overall population sizes of these species stays the same. Competition for food, predation and disease are some of the factors which keep the population size stable.

His third observation was that all living things vary slightly in colour, shape, size or behaviour. For example, Malabar Giant Squirrel which occurs in southern Western Ghats, India, has a dark body coat, whereas, in northern Western Ghats and Eastern Ghats it is slightly paler with white tail tip. Similarly, a group of frogs from the genus Philautus occurs in the Western Ghats and shows quite a lot of variation in their body colour.

Darwin's fourth observation was that many features are passed on from the parent to offspring. Some inherited characteristics are quite easy to see in humans such as eye and hair colour. However, some characteristics, like blood group, are not visible to the naked eye.

Based on these observations, Darwin came to two main conclusions. Every organism on earth is involved in a struggle for survival and some individuals of a species are better adapted than other individuals to their environment. The individuals that are better adapted to their environment are most likely to survive and have a chance to reproduce, hereby, passing on their useful adaptations to the next generation. Those who are less well adapted do not survive long enough to breed. These ideas formed the basis of Darwin's theory of evolution by natural selection.

Darwin concluded that natural selection could explain how organisms gradually change and evolve into new species. When Darwin published his theory, he found it difficult to get it accepted by the scientific community, especially, on how individuals pass their characteristics to the next generation. In the 1930's, after the rediscovery of G.H. Mendel's pioneering work on genetics, Darwin's theory was broadly accepted. Since then advancement in genetics has provided several evidences to support Darwin's theory, however, modern day biologists working on evolution deal more at the gene level and not at the morphological level.

The author can be contacted at jegan@ncf-india.org

Charles Robert Darwin was born on February 12, 1809, in England. Darwin Day is celebrated in memory of Darwin's birthday and to highlight his contribution to science as well as to publicise science in general. Workshops, symposia, lectures, debates and several other events are conduced related to Darwin's work all over the world on this day. For more details visit www.darwinday.org

Although Darwin is best known for his The Origin of Species, he also published other interesting and important books such as Fertilization of Orchids (1862), Descent of Man (1871), Insectivorous plants (1875) and Forms of Flowers (1877). For access to Darwin's complete scientific works and a virtual bookshelf of his books visit http://www.darwin-online.org.uk/