Darwin’s Theory of Evolution

Darwin made important observations and drew inferences from them, which helped him in developing his theory of evolution.

The commonness of many features from anatomical to molecular is a clear indication that all organisms evolved from a common ancestor. Darwin concluded that living forms were not created but evolved by descent with modification from ancestral forms going back all the way to the earliest life more than 3.5 billion years ago.

Darwin’s next question that needed an answer was - What is the mechanism by which the origin of species by descent with modification could take place? Darwin suggested two very important points with regard to evolution:

  1. All living beings are related through ancestry.

  2. The mechanism which causes diversification of species from ancestors is Natural Selection.

Darwin made four important observations on his travel on the ship HMS Beagle:

  1. All organisms tend to produce more offspring than can possibly survive. For example, only a few frog’s eggs survive and become frogs.

  2. In fact, population numbers tends to remain fairly constant over long periods of time.

  3. Also, organisms in a species show wide variation in characteristics.

  4. Some of the variations are inherited, and so passed on to the next generation.

From these observations Darwin made two following deductions:

  1. Since most offspring do not survive, all organisms must be going through a struggle for survival, being eaten, suffering from disease and competition. The struggle for existence cause large number of individuals to die.

  2. The ones who have characteristics that allow them to survive and reproduce better (i.e. possess most useful adaptations for surviving in the environment) will pass on these characteristics to their offspring. In other words, Nature selects the fittest individuals of the population. Natural Selection is the same as the famous phrase "survival of the fittest" coined by Herbert Spencer. Organisms with slightly less survival value will probably perish first, leaving the fittest to pass on their genes to the next generation.

Therefore, the best adapted individuals were selected by nature to survive and leave offspring for the next generation. Darwin called this mechanism Natural Selection.

In Darwin’s time it could not be demonstrated that Natural Selection was the mechanism by which organisms evolved, but later scientists were able to find support for Darwin’s theory in nature as well as in laboratory experiments.

Charles Darwin (1809 - 1882)

Charles Darwin is, like Isaac Newton in Physics, a giant in Biology, whose theory of evolution revolutionized our understanding of life and its diversification on earth.

Darwin was born in Shrewsbury, England on February 9, 1809. He developed a passion for nature from early childhood, a trait he probably inherited from his grandfather Erasmus Darwin. His father wanted him to study medicine at Edinburgh but Darwin did not have the aptitude for it. He also did not pursue studies to become a cleric, his father’s second choice. Darwin was offered the position of a naturalist on board the ship HMS Beagle which he accepted with excitement and enthusiasm.

The voyage on HMS Beagle was a major turning point in Darwin’s life. During the five years (1831-1836) of its voyage he discovered rare fossils in Andes Mountains, collected fascinating animals and plants in Atlantic rain forests of Brazil and made observations on the geographic variation in the famous Darwin’s finches on Galapagos Islands. Darwin gained from all these experiences valuable insights and scientific support for the theory of evolution he was formulating.

Upon return to England, Darwin started accumulating more scientific material in support of his theory of evolution through a mechanism that he called natural selection. Darwin’s famous book on "Origin of Species" was published in 1859.

Darwin died in 1882 at the age of 73. He was given state funeral and was buried in Westminster Abbey next to the grave of Isaac Newton.