Darwin set out his main arguments in Chapters 2 and 3 of The Origin of Species. He stressed a number of key aspects: the struggle for existence, variation, natural selection, extinction and species divergence. These ideas are woven into a very readable and perceptive text that gives an account of his biological knowledge and his experience of the breeding techniques of pigeon fanciers and farmers.
A few short quotations from the Origin are given below which give the core of the theory. They are taken from Darwin’s first edition of 1859.
Owing to the struggle for life, any variation, however slight and from whatever cause preceding, if it be to any degree profitable to an individual of any species, in its infinitely complex relations to other organic beings and to external nature, will tend to the preservation of that individual, and will generally be inherited by its offspring. (p115)
The preservation of favourable variations and the rejection of injurious variations, I call Natural Selection. Variations neither useful nor injurious would not be affected by natural selection, and would be left a fluctuating element... (p131)
It follows that as each selected and favoured form increases in number, so will the less favoured forms decrease and become rare. Rarity, as geology tells us, is the precursor to extinction. (p153)
According to my view, varieties are species in the process of formation, or, as I have called them, incipient species (p155)
This results in a ‘branching-tree’ view of evolution, rather than a step-ladder of progress, or a series of isolated ‘special creations.’ The key ingredients in the scheme, then, are:
Variations occurring spontaneously, not themselves directly produced by the environment
Competition for resources, so that only the best adapted survive to reproduce
Therefore, ‘selection,’ by the environment, of which variants will survive and increase in number.
A few short quotations from the Origin are given below which give the core of the theory. They are taken from Darwin’s first edition of 1859.
Owing to the struggle for life, any variation, however slight and from whatever cause preceding, if it be to any degree profitable to an individual of any species, in its infinitely complex relations to other organic beings and to external nature, will tend to the preservation of that individual, and will generally be inherited by its offspring. (p115)
The preservation of favourable variations and the rejection of injurious variations, I call Natural Selection. Variations neither useful nor injurious would not be affected by natural selection, and would be left a fluctuating element... (p131)
It follows that as each selected and favoured form increases in number, so will the less favoured forms decrease and become rare. Rarity, as geology tells us, is the precursor to extinction. (p153)
According to my view, varieties are species in the process of formation, or, as I have called them, incipient species (p155)
This results in a ‘branching-tree’ view of evolution, rather than a step-ladder of progress, or a series of isolated ‘special creations.’ The key ingredients in the scheme, then, are:
Variations occurring spontaneously, not themselves directly produced by the environment
Competition for resources, so that only the best adapted survive to reproduce
Therefore, ‘selection,’ by the environment, of which variants will survive and increase in number.
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