Neo-Darwinism / R.J. Berry.

  • Berry, R. J. (Robert James)
Date:
1982
Catalogue details

Licence: Attribution-NonCommercial 4.0 International (CC BY-NC 4.0)

Credit: Neo-Darwinism / R.J. Berry. Source: Wellcome Collection.

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    DARWIN'S OWN ANSWERS 5 produced by the attempts of animals to increase the development of their own organs, and thus modify their structure and habits - has been repeatedly and easily refuted by all writers on the subject of varieties and species, and it seems to have been considered that when this was done the whole question has been finally settled; but the view here developed renders such an hypothesis quite unnecessary, by showing that similar results must be produced by the action of principles constantly at work in nature . . . (For example) the giraffe did not acquire its long neck by desiring to reach the foliage of the more lofty shrubs, and constantly stretching its neck for the purpose, but because any varieties which occurred among its antetypes with a longer neck than usual at once secured a fresh range of pasture over the same ground as their shorter-necked companions, and on the first scarcity of food were thereby enabled to outlive them.' 'We believe we have now shown that there is a tendency in nature to the continued progression of certain classes of varieties further and further from the original type - a progression to which there appears no reason to assign any definite limits . . . This progression, by minute steps, in various directions, but always checked and balanced by the necessary conditions, subject to which alone existence can be preserved, may, it is believed, be followed out so as to agree with all the phenomena presented by organised beings, their extinction and succession in past ages, and all the extraordinary modifications of form, instinct, and habits which they exhibit.' 1.2.3 The essence of evolutionary mechanism Both these papers clearly contain the three facts and two conclusions which are commonly taken as the simple summary of Darwinism evolution: the potential of all species to increase greatly in numbers, coupled with an approximate constancy of numbers, implies that there is л struggle for existence', and when variation is added to this, it is clear ihoXnaturalselection must operate. It was the ease with which these propositions could be understood that helped the fact of evolution to be generally accepted. In fact Darwin devoted more than half of the Origin to different lines of evidence that evolution has occurred: he has two chapters on the fossil record, two on geographical distributions, and one each on morphological likenesses (including comparative embryology, the interpretation of vestigial organs, and the meaning of classification), behaviour, and domestication. He devoted later books specifically to the origin of man and sexual selection, domestication, and adaptations in plants for pollination, insect-eating, and climbing. All these were parts of the book Darwin had originally intended to write before being forced into print by Wallace. 1.3 First series of objections: Darwin's own answers In Chapters 6 and 7 of the Origin Darwin deals with 'difficulties' and 'mis¬ cellaneous objections' to his theory. His main points concern the nature of species and questions about the efficacy of selection. In a later chapter, he discusses the imperfections of the fossil record. Darwin knew that the