On the Origin of Species By Charles Darwin(Free)

Charles Darwin was not the first to come up with the concept of evolution. Many scientists, including Darwin’s grandfather, had accepted that plants and animals on Earth had changed form over time. Already in 1809, Jean-Baptiste Lamarck had argued that modern animals, including humans, had descended from other species. Lamarck promoted the idea of “inheritance of acquired characteristics” as the mechanism governing this evolution. For example, Lamarck argued that the neck of a giraffe stretching for food would eventually lengthen slightly, a physical characteristic that would be passed to its offspring.

In On the Origin of Species by Means of Natural Selection, better known as On the Origin of Species, Darwin achieves two things that Lamarck does not. He gathers detailed evidence to support evolution and offers a different, and ultimately workable, mechanism to govern it. This mechanism, natural selection, has been supported by later research, whereas Lamarck’s idea of inheritance of acquired characteristics has not. Natural selection is believed to be the major (but not only) force driving species evolution.

Natural selection is a simple concept. Consider animals. First, individuals of any species vary in size, coloration, behavior, and other characteristics. Second, these variations tend to be passed on to an individual’s offspring. Third, more offspring are born than those surviving to reproduce. Fourth, any characteristic (such as coloration) that allows one individual to survive better than others will help that individual reproduce more. Fifth, this characteristic will increase in frequency in the species over time.

Natural selection has been observed in many species. The finches of the Galapagos Islands provide a good example. The Galapagos finches are a group of closely related bird species that helped Darwin discover natural selection. These birds differ primarily in behavior and in beak size and shape. In dry years, heavier-beaked finches survive and reproduce better because they can open bigger seeds. Average beak size can change dramatically over a single breeding season. This illustrates natural selection.