Take a moment and try to observe your surroundings. What will you find? You might see different types of plants around you. All the plants are so similar yet so distinct from each other. Similarly, you might resemble your parents a bit but look so different from your friends and colleagues. How is it possible? How does this diversity arise? The answer to all these unique questions might have some underlying evolutionary phenomenon. Evolution refers to the study of changes taking place in a species over several generations. Charles Robert Darwin is credited to be the ‘Father of Evolution.’ Darwin was a naturalist and a biologist who was born on 12th February 1809, in The Mount, Shrewsbury, Shropshire, England. He focussed on understanding the origin of life on the earth and also wrote extensively about it. Charles Darwin put forth the theory of evolution in his widely acclaimed book, ‘The Origin of Species‘, published in 1859.
Today, we are going to discuss the theory of evolution.
1. The Theory of Common Descent
According to the theory of common descent, Darwin stated that all the organisms, which live on earth, have descended from a common ancestor. With time, the organisms started accumulating some changes and grew different from each other. These changes were beneficial for their survival with the changing environment. Different species arose by the process of speciation. However, only those species survived which had a certain degree of adaptation present in their organization and were reproductively fit. The history of life, right from the beginning, is represented in the form of a branching tree known as phylogeny. The most important example of common descent is the similarities, in the pattern of bones of forelimbs of whales, bats, Cheetah, and humans share.
Homologous features: When different species share a physical feature, it is possible that this particular feature might have been inherited from a common ancestor; for example, vertebrate hearts and brains have evolved from a common ancestor.
Analogous features: Interestingly, the physical features which look so similar might not have evolved from a common ancestor. Such features are known as analogous features; for example, flippers of penguins and dolphins have similar functions but have evolved from different ancestors.
2. The Theory of Gradualism
Gradualism explains that new species arise with slow and gradual changes in the population and not the sudden production of new organisms. Darwin’s theory of gradualism defied the principle of the sudden appearance of species. The minute changes that are continuously occurring in the populations of organisms are called the ‘raw material’ for the evolution of new species. The accumulation of changes governs the origin and evolution of new species. With some time, when different changes accumulate continuously and result in adaptation, the species are said to have evolved. Darwin stated that the accumulation of quantitative changes leads to qualitative changes. Therefore, evolution can be rightly referred to as a ‘gradual process.’ 
3. Multiplication of Species
Once the new species arise, they split up into daughter species. The multiplication of species follows the principle of common descent. A branch point in the phylogenetic tree is an indication that the ancestral species has split into two new and different species. Darwin proposed that the new species result because of the genetic variations in the species of the geographically separated populations. Since evolution is represented as the branching process, therefore, the number of new species increases with time. Various reproductive barriers prevent different species from interbreeding. The most interesting example is that of Darwin’s finches. Darwin observed small black birds, which he referred to as Darwin’s finches, on the Galapagos islands. There were many varieties of the finches which evolved on the island only. Many different varieties arose from the seed-eating original species of bird. The new varieties had modified beaks depending upon their eating habit.
4. The Theory of Natural Selection
One of the most important aspects of Darwin’s theory of evolution is ‘natural selection.’ It encompasses all kinds of developmental, behavioral, anatomical, and physiological adaptations which enhance the ability of an organism to utilize environmental resources for survival and reproduction. It is the nature which has the power to select the most beneficial adaptation and amplify the survival rates of those organisms with the beneficial adaptations. One of the common examples of natural selection is the decrease in numbers of white-winged moths during the industrialization in England in 1920. Before the era of industrialization in 1850, the number of white-winged moths was more as compared to the dark-winged moths. However, after 1920, the number of dark-winged moths increased. This happened because the trunk of the trees turned darker due to industrial soot and smoke. The predators could easily spot the white-winged moths against a dark background whereas the dark-winged moths were harder to spot. However, before industrialization, white-colored lichens thickly covered the trees in England; making the dark-winged moths easy to spot and rendering selective advantage to the white-winged moths.
