Evolution is the natural process by which an organism evolves from one form to another gradually. It is a complex biological process in which an organism inherits different features of its ancestors. It can be also seen as the way how a living being responds to the environmental changes around him. It is just the nature’s way of defining the rule 'survival of the fittest'. According to a few researchers, all living forms on earth, evolved from a single ancestor called LUCA (Last universal common ancestor), which lived approximately 4 billion years ago.
There have been many theories on evolution, but the one described by Charles Darwin in his book ‘On the Origin of Species’ is observed to be the foundation of evolutionary biology. In this work, Darwin described his scientific theory of how the population evolved by a process of natural selection along the generations. In this book he justified how diversity of life evolved from a single ancestor. There were a few modifications made to this theory of natural selection in the early 20th century named as the modern evolutionary synthesis after which the importance of natural selection was accepted by the other branches of biology. To get an in-depth knowledge about the topic, read these famous evolution quotes.