Many years ago, some pre-Socratic philosophers were among the first to propose that one kind of animal could come from a different animal. These include Greek philosophers such as Empedocles and Anaximander. In contrast, Aristotle had an understanding that all natural things were imperfect actualizations of varying fixed possibilities, namely species, forms or ideas. Titus Lucretius Carus, a Roman philosopher and poet suggested the likelihood of evolutionary modifications of organisms. During the middle ages, the dissimilarities of this idea grew to become the general understanding and were incorporated into Christian learning. However, Aristotle didn’t suggest that real animals were related one-for-one with the same metaphysical forms and specific examples was given to show how new form of living things would come into existence.

In the seventeenth century, Aristotle’s approach was rejected by the new method for modern science. As of such, explanations were sought for natural phenomena as it pertains to the laws of nature, which were similar for all visible things. However, the new approach took roots slowly in the biological sciences and became the final support for the idea of fixed natural types. In addition, Carolous Linnaeus introduced a biological classification in 1735 which look at fixed species as part of a divine plan.

Later on in 1842, Charles Darwin recorded his first sketch of “On the Origin of Species”. There were other naturalists during this period who were speculating on the evolutionary modification of species overtime based on the natural laws. In 1751, Maupertuis wrote about natural changes taking place during reproduction and growing throughout many generations to create new species. Erasmus Darwin suggested that warm blooded animals could descend from one filament or micro-organism. Buffon proposed that species can degenerate into many different organisms. Lamarck transmutation theory during 1809 was the first full-grown evolutionary scheme that envisaged generations producing simple life forms continually and spontaneously to develop more complexity in similar lineages with a natural progressive tendency. There was also the belief that these lineages would adapt to the environment on local levels by inheriting the changes caused by disuse or use in parents.

Some established naturalists condemned those ideas as speculations which lack empirical support. The crucial break from the idea of fixed species in biological science started when Charles Darwin formulated the evolution theory by natural selection. Darwin noted that the growth in population would cause a struggle for survival where favorable variants could prevail while others perished. In every generation, a number of offspring would die before reaching the reproduction age due to limited resources. From this perspective, one could understand the diversity of plants and animals from one common ancestry based on the notion that the natural laws are working the same way for all things.

Moving along from 1838, Darwin was working to develop his natural selection theory until he received a similar theory from Alfred Russel Wallace in 1858. The two men presented separate work to the Linnean Society in London. Charles Darwin’s On the Origin of Species publication came out in the later part of 1859 with an in-depth explanation of the natural selection theory. To some extent, this contributed to a wide acceptance of the Darwinian evolution. Darwin’s philosophies were applied to humans by Thomas Henry Huxley when he used paleontology and proportional anatomy to give strong evidence that apes and humans shared one common ancestry. This disturbed many because it was implying that humans didn’t have a special standing in the universe.

Since there were no findings to show the origin of the new traits and accurate reproductive heritability mechanisms, Darwin developed a short-term theory of pangenesis. Gregor Mendel noted that traits were inherited predictably through independent collection and separation of elements (genes). The inheritance laws from Mendel eventually superseded most of the pangenesis theory. August Weismann made an important distinction between somatic cells and germ cells (eggs and sperms) to show that heredity is only passed throughout the germ line. Darwin’s pangenesis theory and Wiesman’s soma & germ cell distinction was connected by Hugo de Vries who proposed that the pangenesis were concentrated in cell nucleus and they could enter the cytoplasm to make changes to the cells structure when expressed. De Vries also believed that Mendelian traits were connected to the transfer of inherited variations throughout the germ line. Moreover, De Vries formulated a mutation theory to explain the origin of new variants and this caused a temporary rift between his supporters and those who agreed with the Darwinian evolution.

At the turn of the twentieth century, the foundations for evolution were set on a strong statistical philosophy by population genetics pioneers, such as Ronald Fisher, J.B.S. Haldane and Sewall Wright. This reconciled the false contradictions between Mendelian inheritance, Darwin’s theory and genetic mutations.

During the 1920s and 1930s, natural selection, Mendelian inheritance and mutation theory was connected by a modern evolutionary synthesis to form a unified theory that would be generally applied to any area of biology. This modern synthesis explained the patterns detected across species in the populations through fossil changes in palaeontology and complex cellular systems in developmental biology.

In 1953, Francis Crick and James Watson introduced a publication about the DNA structure to demonstrate a physical origin of inheritance. In addition, advancements in phylogenetic systematics showed the mapping of traits transition into a testable and comparative structure through the publication and the usage of evolutionary trees. Theodosius Dobzhansky, an evolutionary biologist, noted in 1973 that except for evolution, nothing makes sense in biology.

The modern synthesis was extended further since then to explain the biological occurrences across the complete and integrative spectrum of the biological hierarchy, starting from the genes to the species.