The theory of evolution, recognized today as a process of changethat develops living things over time, was presented by Charles Darwin in his1859 book On the Origin of Species.
Darwin was an English naturalist whose father was a physician and whosegrandfather was also a physician and a philosopher who pondered the developmentof species. In his 30s, the younger Darwin travelled on the ship, the HMS Beagle, to South America and spent muchtime in the Galapagos Islands studying finches and tortoises. He was struck byhow slightly different the animals were on each of the many islands of the archipelago,specifically the beaks of the finches seemed adapted to the shape of their foodsource. “How does this change take place?” he wondered. He posited that theform of the birds changed over generations, because in each generation thebirds with the beaks most closely matched to their food source were more ableto provide food, attract mates, and reproduce, thereby pass their beak-shape tothe next generation. Birds with unfavorable beak shapes would fail to thrive,in general have a harder time attracting a mate, and were less likely to passtheir beak-shape to the next generation. In fact, the title of Darwin’s book inits entirety is On the Orgin of Speciesby Means of Natural Selection, and introduces the term ‘natural selection’to explain how desirable traits, programmed at birth but selected for by mates,are passed on to the next generation.
The theory is also referred to as the ‘survivalof the fittest’ because traits that make an individual successful in life aregenerally the most desired by mates. At some point, Darwin observed, thefinches became significantly enough different or isolated from their originalrelatives that they were no longer able to or interested in interbreeding, thetypical inception of a new species. Darwin wasn’t sure of the biologicalprocess for passing on or affecting the beak-shape of the next generation; thatwas left for future theorists. Prior to Darwin’s theory, rumination of the differences in livingthings goes back to Greek philosophers in about 600 BC. Anaximander ofMiletus suggested that humans must have developed from animals of another sortbecause they need such care and nursing as infants. Plato believed in speciesas Forms that aspire to be of a perfect, defined shape and that those Forms don’tchange over time. His student, Aristotle (384-322 B.
C.), presented ideas thatare the most well-preserved and well-developed of the time. He described hisidea as a ladder or “scale of life” with insects and plants at the bottom(simple, or less perfect) and mammals and humans at the top (complex or moreperfect). He believed that the number of species and their forms, which wereconstant over time, were fixed rungs of the ladder with each having its ownpurpose and place in nature, an idea later referred to as the Great Chain ofBeing. This idea was generally accepted for almost 2000 years, regularlyintertwined with religion, that species were designed by God when He createdthe earth, and were ordained for specific roles in life as determined byHim. In the 1700s, the Swede Carl Linnaeus developed the idea oftaxonomy, the naming and classification of similar species into a tree of relatedness.By the late 1700s, several scientists, Comte de Buffon and Erasmus Darwin, werethe first to explore the idea that species changed over time. Their ideas werenot formally published because of the pushback they feared from the church andreligious followers who still subscribed to the ordained and unchanging rolesof Great Chain of Being.
Transmutation, or transformation, was the dominant theory of theearly 1800s as proposed by Jean-Baptiste Lamarck in his Philosophie Zoologique (1809). The fully-formed evolutionary theorybuilt on the Great Chain of Being idea, and included the tenant thatindividuals adapt physically to their environment within their lifetime and passthose adaptations on to their offspring via a “life-force” fluid. The majordifference between transmutation and Darwin’s theory was that it didn’t includebelief in the existence of a common ancestor, instead that living things haveparallel (separate but similar) paths of evolution over time, families whosemembers graduate up the Chain of Being. About the same time as Darwin’s famous publication, Wallace alsopublished his ___ theorizing ___.
Although the ideas presented by Darwin and Wallace went against commonthought at the time, within about ten years evolution was generally accepted asfact by the scientific community and a large part of the public.