Evolution

Evolution is the way living organisms change over time, driven by natural selection.

A revolutionary insight put forward by Charles Darwin in On the Origin of Species in 1859, the concept of natural selection was also touted by another British naturalist, Alfred Russel Wallace, who had come up with the idea at the same time.

The two men hit upon a mechanism for evolution: all organisms vary and some variations are more beneficial than others, helping individuals thrive and preferentially pass them on to the next generation. In other words, these variations are naturally selected. (Darwin later outlined a similar mechanism, “sexual selection” whereby variations considered more attractive to the opposite sex are more likely to be passed on.)

Natural selection requires that beneficial characteristics be passed from one generation to the next intact. It was not clear to Darwin how this might happen. However, at around the same time an Augustinian monk called Gregor Mendel was conducting experiments that held the answer. In 1866, he published results from studies of inheritance in pea plants, marking the birth of modern genetics. His discoveries went unnoticed for over three decades. Not long after they were rediscovered, genes were identified as units arranged along the chromosomes inside the cell’s nucleus. And in 1937, the “modern synthesis” brought these ideas together, defining evolution in genetic terms as the “change in the frequency of an allele [gene variant] within a gene pool”.

Though it was made famous by Darwin, the idea of evolution actually predates him. By the early 19th century, developments in geology and mining had revealed Earth to be inconceivably ancient. It was also found to have changed over time, along with the forms of life that lived on it. One of the first people to try to explain how new species formed was Erasmus Darwin, Charles’s grandfather. Another influential early evolutionist was the French naturalist Jean-Baptiste Lamarck, whose “transmutation of species” theory famously argued that change occurs when characteristics acquired during an organism’s lifetime are passed on to its offspring.

In recent years, the theory of evolution itself has evolved. The idea that it is entirely driven by natural selection is challenged by new discoveries in genetics, epigenetics and developmental biology. There is growing evidence that genes do not have sole control over development and heredity, and that organisms play active roles in their own fate and that of their descendants. As a result, a growing number of biologists believe we need to extend our ideas of how evolution works.

Evolution also faces a challenge from the rise of the religious creationist movement, which believes in the Bible’s account of the origins of life of Earth, and rejects evolution on this basis.