The Origin of Species

"On the origin of species by means of natural selection, or the preservation of favoured races in the struggle for life" is the title of the book in which Charles Darwin explains his theory on evolution by means of natural selection, first published in 1859.   Darwin published the book as an abstract to a planned more voluminous work, which would list all the evidence in favour of the theory that he had collected. Nevertheless, The Origin summarizes a vast number of facts and observations, collected by the author and friends like Joseph Dalton Hooker and T.H. Huxley, which convincingly illustrate the idea of evolution. Unlike many great works of science, often made inaccessible through the use of technical jargon and advanced mathematics, The Origin is a very readable book, which greatly benefits from Darwin's obvious enthusiasm for the great wealth of forms and organisms in nature. This, among other reasons, made it a great success with the general public of the time.

For details on the conception of the theory and the events that led to the publication of The Origin see the main article on Charles Darwin.

Contents of The Origin of Species

The book starts with a short introduction which briefly explains why Darwin published the book, the purpose of its form (being an abstract to a larger work) and the basic elements of the theory as well as the major sources of evidence in favour of the idea. In later editions a historical sketch was added, in which Darwin enlists, in a reaction to his critics, over thirty people who before him formulated ideas about evolution and the origin of species.

The first two chapters of the book deal with the presence of variation in all organisms. First he deals with the presence and selection of variation in domesticated plants and animals by humans and explains that through this process new varieties arise. The second chapter then shows that similar variation exists in nature and briefly discusses under which circumstances the variablity of a species may increase.

The third chapter applies the ideas of Robert Malthus, about population growth and food supplies, to all natural populations and explains that this must lead to a struggle for existence. The struggle is however not just between members of the same species, but must be fought between all species because of the intricate relations that links each species to the others. In this sense Darwin could be seen as one of the founding fathers of the, then not yet existing, science of ecology, as he firmly establishes his theory within the framework of the interspecific interactions that are the object of ecological studies.

After having established that variation (termed divergence of character) exists in all organisms and that these organisms must compete against each other in order to survive, the fourth chapter explains that the forms that are better adapted to their circumstances will be selected to produce offspring, simply by being more vigorous then all the others. The struggle for life will cause less well adapted forms to go extinct and leaves the better forms to continue adapting (unconsciously and without direction) to their environment.

The Origin was published prior to the work of Gregor Mendel and there was little or no knowledge available on genetics, so the fifth chapter discusses the laws of variation in relatively vague terms and basically covers the correlations of growth, the fact that different developmental stages should affect each other and that specific traits are more variable than generic traits are.

From Chapter Six onwards Darwin discusses the difficulties with his theory, concentrating subsequently on instinct, hybridism, the geological record, geographical distribution of organisms and finally the difficulties of classification of organic beings and the existence of rudimentary organs, trying to awnser each problem as justly and adequately as he could.

In his chapter on instincts Darwin explains that not only physical traits, such as the length of a limb, are affected by natural selection, but also the mental capacities of animals. He gives the interesting example of how the complex structure of the hive of the hive-bee, which is apparently the most economical structure possible in the use of wax, could have evolved from the simple sherical structures still made by humble-bees. Additionally, from the examples of neuter individuals in insect groups, but also the slave making habits of some ant species, Darwin clearly makes a case for mulltilevel selection, a point which was later also advocated by Stephen Jay Gould.

After lengthy discussion of these difficulties, Darwin recapitulates these in the final chapter and than briefly discusses the causes of the then widespread belief in the immutability of species and remarks on the scope within which the theory of natural selection can be applied. In order to reach a broad public Darwin included a short glossary of scientific terms, which was produced by W.S. Dallas.

Reactions

How extremely stupid not to have thought of that - T.H. Huxley

For more reactions on The Origin see the main article on Charles Darwin.