The history of evolutionary thought has endured from antiquity, since the idea of biological evolution has derived as a philosophical idea since the Ancient Greek and Roman eras. Scientific formulations of the idea did not arise until the 18th and 19th centuries, when scientists such as Lord Monboddo and Erasmus Darwin, Charles Darwin's grandfather, proposed that living organisms were derived from a common ancestor. A hypothesized mechanism for biological descent with modification was proposed by Jean-Baptiste Lamarck, who suggested that organisms inherit the characteristics acquired by their parents during the course of life. This since-discredited hypothesis is referred to as inheritance of acquired characteristics. The modern theory referred to as Darwinism was first publicly put forth by Charles Darwin and Alfred Russel Wallace and discussed in great detail in Darwin's later publications, including his most famous exposition of the theory, On the Origin of Species. Darwin emphasized the difference between two main points: establishing the fact of biological evolution, and proposing the theory of natural selection to explain its mechanism
Although Darwin's theory offered a substantive explanation of a wealth of biological observations, the mechanism of biological inheritance was not yet known at the time of his work; although the person commonly considered the originator of modern genetic theory, Gregor Mendel, was a contemporary of Darwin, Mendel's work was largely neglected until the early 20th century. The combination of the Darwinian proposal of natural selection with classical genetics is known as the modern synthesis. Later work identified the gene, or the basic unit of inheritance in organisms, as encoded in DNA molecules carried by all living cells; subsequent work in molecular genetics has led to additional work in evolutionary theory such as the neutral theory of molecular evolution, which presents a role in biological evolution for genetic drift as well as natural selection.