Not long ago, it was thought that God created all species. That changed in 1858, with the remarkable “Theory of Evolution”. It is the most revolutionary concept in the history of science. Nothing else has more radically changed our understanding of the natural world and ourselves. A theory is an idea about how something in nature works that has gone through various testing and observations with experiments designed to prove the idea right or wrong. When it comes to the evolution of life, various philosophers and scientists proposed different aspects of what later would become evolutionary theory. But evolution did not reach the status of being a scientific theory until the famous Charles Darwin, published his book On the Origin of Species in 1859. This article covers the path that led Darwin to the theory of evolution, what ideas he built on, who all added to these theories of evolution and how was this concept accepted by the scientists during those times.
The English naturalist Charles Darwin's "Theory of Evolution" was once described as "the single best idea anyone has ever had”, which proposes that all life including humans, is related and is descended from a common ancestor. Before Darwin's theory, published in "On the Origin of Species" in 1859, it was believed that man came from an archetype created by God, and was set apart from animals. His theories showed creation had taken longer than the Biblical seven days and that man was likely to be descended from apes. Darwin with his scientific contemporary, Alfred Russel Wallace, proposed that evolution occurs because of a phenomenon called natural selection. Although, before this discovery of modern evolution, several Greek writings and some theories of evolution emerged during the mid-16th century.
Charles Darwin, carbon-print photograph by Julia Margaret Cameron, 1868.
Image: Courtesy of the International Museum of Photography at George Eastman House, Rochester, New York
Evolutionary concepts were first seen in early Greek writings, for example, in the work of Anaximander and Empedocles. The former proposed that animals could be transformed from one kind to another, while the latter speculated that they could be made of various combinations of pre-existing parts. However, for several years subsequent theories were restrained from developing and challenging the belief of special creation, due to the restraining influence of the Church. Although, the growth of scientific observation and experimentation led to some theories of evolution beginning to emerge after the mid16th century.
Pierre-Louis proposed the spontaneous generation and extinction of organisms as part of his theory of origins, but it didn't advance to the evolution part. Erasmus Darwin, grandfather of Charles Darwin, offered some evolutionary predictions in his book Zoonomia, but it had no real influence on further theories. A clearly stated evolutionary theory was presented by Jean-Baptiste Lamarck, which was although disapproved strongly then but later came to be known as ‘The Inheritance of Acquired Characteristics' and was used in further studies. After this came Charles Darwin who revolutionized the concept of Evolution with his 1859 book “On the Origin of The Species”, although another naturalist Alfred Wallace had also hit upon the idea of natural selection independently, but his view differed from Darwin’s, most notably in that he did not believe that natural selection was sufficient to account for the origin of humans, but divine intervention had been required.
Charles Darwin’s Theory
The founder of the modern theory of evolution was Charles Darwin. On December 27, 1831 he sailed as a naturalist aboard the HMS Beagle on a round-the-world trip that lasted until October 1836. The discovery of fossil bones from large extinct mammals in Argentina and the observation of extensive species of finches in the Galapagos Islands were among the occurrences credited with challenging Darwin’s interest in how species originate. The intellectual challenge was to explain the origin of distinct species of organisms and how new ones adapted to their environments. Darwin considered natural selection, over his demonstration of evolution, his most important finding and designated it as “my theory,” a denotation he never used when referring to the evolution of organisms. Until his death, he dedicated to substantiating natural selection and its other postulates, mainly the universality of hereditary variation and the enormous fertility of organisms, which greatly exceeded the capacity of available resources.
Fourteen species of Galapagos finches that evolved from a common ancestor.
Image: Encyclopedia Britannica, Inc.
Alfred Wallace: a distinction with a difference
Wallace is famously given credit for discovering natural selection as the process accounting for the evolution of species, separately than Darwin. In 1858, he came upon the idea of natural selection as the explanation for evolutionary change. He was not interested in explaining design but rather in accounting for the evolution of species and also thought that evolution proceeds indefinitely and is progressive. Darwin, on the contrary, did not believe that evolution would necessarily represent progress or advancement, nor did he believe that evolution would always result in structural change over time; rather, he knew of the existence of “living fossils,” that had
remained unchanged for millions of years.
On the Origin of Species
The evolution written by Darwin is due to two factors. The first factor, he argued, is that each individual animal is marked by slight differences that distinguish it from its parents. Darwin, who called these differences “variations,” understood their effect but not their cause; the idea of genetic mutation, and the study of genetics, was not raised fully until the early 20th century.
The second factor, Darwin argued, is that although variations are random, some of them result in
distinct advantages – superior camouflage, a livelier constitution or greater speed that would help the creature to adapt better. A greater chance of survival allows for more chances to breed and pass on advantageous traits to a greater number of offspring.
Over time, this trait spreads throughout a species which eventually makes the species more likely to sustain and reproduce. Thus, over the course of many generations, small changes occur and accumulate, eventually leading into bigger changes and maybe even a new species. The publication of the Origin of Species produced considerable public excitement. Scientists, politicians and notables of all kinds read and discussed the book, defending or disdaining Darwin’s ideas.
Title page of the 1859 edition of Charles Darwin's On the Origin of Species
Image: Library of Congress, Washington.
What lacked in Darwin's theory?
The most serious difficulty faced by Darwin’s evolutionary theory was the insufficiency of an adequate theory of inheritance that may account for the conservation through the generations of the variations, on which natural selection was imagined to act. Contemporary theories of “blending inheritance” proposed that offspring merely struck a mean between the characteristics of their parents. But as Darwin became aware, blending inheritance (including his own theory of “pangenesis,” during which each organ and tissue of an organism throws off tiny contributions of itself that are collected within the sex organs and determine the configuration of the offspring) couldn't account for the conservation of variations, because differences between variant offspring would be halved each generation, rapidly reducing the primary variation to the standard of the preexisting characteristics.
The idea of Evolution bought above by Charles Darwin can indeed be defined as a magnificent idea as it enlightened as with the fact that all forms of life, including humans are related to each other and have descended from a common ancestor. With Darwin's discovery of natural selection, the origin and adaptations of organisms were brought into the domain of science. The adaptive features of organisms could now be explained as the result of natural processes, without help of an Intelligent Designer.
Therefore, theory of evolution accounts for the “design” of organisms, and for their immense diversity, as the result of natural processes, the gradual collection of spontaneously arisen variations (mutations) sorted out by natural selection. The characteristics that will be selected depends on which variations happen to be present at a given time in a given place. This in turn depends on the random process of mutation and previous history of the organisms. Mutation and selection have together driven the wonderful process that, starting from microscopic organisms, has yielded plants, birds, and humans.
The theory of evolution thus conveys chance and necessity, randomness and determinism, jointly tangled in the stuff of life. This was Darwin's fundamental discovery, that there is a process that is creative, although not conscious.
Department of Biochemistry and Biotechnology
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