Neo-Darwinism / R.J. Berry.

  • R. J. Berry
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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    THE EVIDENCE FOR EVOLUTION 55 6.5 The evidence for evolution We have already noted that Darwin convinced those of his colleagues prepared to accept evolution by putting forward a believable mechanism for change as well as by the weight of evidence (section 1.2). We have further seen that the evolutionary syntheses of the 1930s and 1970s depended mainly upon the interpretation of known data rather than the discovery of new facts. Indeed, it is intriguing how little the actual evidence for evolution has featured in the recurring controversies since 1858. Nevertheless it is obviously necessary to ask if the evolutionary interpretations described so far are based on real evidence of evolutionary change. The fossil record in 1858 was poorly known, but the basic outline of the succession of life was well established. Darwin knew that trilobites were confined to the Palaeozoic and dinosaurs to the Mesozic, and many other features of the history of life. When palaeontologists had their eyes opened by Darwin, they turned the known but vaguely defined succession of life in the fossil strata into phylogenies; the classification of animals and plants was reorganized to reflect their evolution, and so-called phylogenetic or natural classifications were proposed for many groups. Darwin sought and largely failed to find evidences of gradual change in fossils, and missing links between groups. He blamed the incompleteness of the fossil record. Several hundred 'missing links' are now known, but it is still true that we have more gaps than transitional forms. However, we now interpret this as the consequence of new species often arising from small populations in isolated areas (section 6.2.2), which is not unlike the answer Darwin himself gave to the problem (section 1.3.1). To some extent, it is possible for palaeon¬ tologists to estimate the degree of incompleteness of the fossil record; when this is done. It is clear that we have an adequate record of most preservable groups and that this supports phylogenies and replacements built from molecular, morphological, and biogeographical data. Nevertheless the record has to be read, and it is susceptible to an interpretation based on work with living populations as far as the nature and speed of particular evolutionary events are concerned (see section 6.2.2). Standard textbooks on evolution devote much space to a discussion of 'homologies' (including vestigial organs), i.e. organs or processes in different groups which have a common origin. Common examples are the constancy of the DNA code, animal cell membranes, the structure of such macro-molecules as haemoglobin, mouthparts of insects, planktonic larvae of marine inverte¬ brates, pentadactyl limb of vertebrates, flower parts of angiosperms, and the gametophyte stage of land plants. These all provide strong circumstantial evidence for evolution, and in toto as convincing a case as any of Sherlock Holmes's. But morphological homologies by themselves have never been very convincing. The problem is that morphology can often be explained by more than one hypothesis; different workers may differ about particular relationships and therefore weaken their use as evolutionary evidence. For example, the structures of lung fish have been a recurring subject for disagreement. However, the enormous mass of evidence from comparative morphology.
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