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 IS EVOLUTIONARY BIOLOGY TRUE?
 

What would happen if Darwin's theory of organic creation were refuted? One of the immediate consequences would be that Bowlby's theory of Attachment would be proven false.

So, what about performing an epistemological exercise whereby we challenge Darwin's theory and contrast it with 3 other rival theories, and see how it fares?

The first great epistemological revolution in biology was undertaken by Lamarck, who advanced the first evolutionary model of organic creation. Before Lamarck the only belief which was held as valid was that of the Bible. There it is asserted that mas was created as man, and each other living species had been created by God just as we can see them today. The Bible (actually the Book of Genesis) certainly denies both parts of the evolutionary hypothesis, transformation of species and the common ancestry of life.

But there is an alternative to the Biblical account, a hypothesis that asserts that species do not change through time, that all species have in the past always looked as they do now; and that species have a separate origin. This is known as the theory of separate creation. Something very loke it was held by the geologist Charles Lyell in the early editions of his work "The Principles of Geology (1830-3)".

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We have already stated that evolution means that all modern species have descended from a single common ancestral species; species have thus changed in appearance as they have descended and diversified through time. According to the theory of evolution, life originated only once and species are not immutable. The present diversity of forms has been produced from one ancestor by the splitting of the species.

It could be that species do change, but that life has originated more than once. Species might change into new species without splitting; the single lineage might las indefinitely, without ever going extinct. Lamarck thought that species never go extinct and speculated that species slowly change into more progressive forms through the mechanism of inheritance of acquired characters. (So did Freud, see his "Totem and Taboo"). The history of life would have been independent creations followed by transformations within each lineage. The transformations would have been the result of adaptations to the environment passed onto the next generation by inheritance. This is known as 'transformism'.

We now have, apart from the Biblical account of the origin of the world (creationism), 3 theories of the history of life. They differ in their answers to the questions of whther species are fixed in appearance or can change over generations; and whether there has been a single ancestor of modern species or several. Separate creation states that species do not change and that there were as many origins of species as there have been species. Trnsformism states that species do change, but that t have been several origins of life. Evolution states that species change, and split into more than one species, and that present-day species are the descendants of a single ancestor.

The best evidence for evolution for evolution would be to see it in action. This has been achieved under both natural and artificial conditions (Maynard Smith 1975). A well known case is that of the peppered moth in Great Britain. This moth exists in two main forms, a dark one and a light one. Before the Industrial Revolution the light form was much the commoner; but throtugh the nineteenth century, in industrial areas, the dark form gradually increased in numbers, to become the commoner form. A comparable degree of evolutionary change has been studied in many other species (Wilson, 1975). In all of them, the appearance of the species has changed through time: they have evolved and been seen to evolve. Similar changes can be produced artificially. A new generation that differs from its predecessor can easily be produced by breeding selectively from certain forms in a population. If one breeds, for example, from only the larger mice of a population, the next generation will have a larger average weight. The evolutionary change can be watched as it takes place. The observation will thus favour the theories of evolution and transformism, but will count against separate creation.

A second argument for evolution comes from taxonomy. Species are classified together if they share certain traits which are called homologies. The era.bones of mammals are an example of an homology. They are homologous woth some of the jaw-bones of reptiles. The ear-bones of mammals did not have to be formed from the same bones as form the jaw of reptiles; but in fact they are. If reptiles and mammals evolved separately, we should not expect to find this similarity. But if mammals evolved from reptiles, we should expect to find otherwise unintelliglible similarities. Clearly the ear-bones evolved from the jaw-bone. THe fact that species share homologies is an argument for evolution, for if they had been created separately, there would be no reason why they should show homologous similarities.

The sheer number of homologous similarities among species kakes a powerful argument for evolution: a giraffe's neck has the same number of vertebrae as the neck of a mouse; a penguin's wing has the same joint structure as a knagaroo's front paw. Take the famous case of the Galapagos finches (Maynard Smith, 1975). There are, on the different islands of htat archipelago, 14 different species of finch. The 14 species fill many of the roles we should expect -on another continent- to be played by other, unrelated birds. One of them, for instance, is a woodpecker finch. It has evolved a long woodpecker-beak but not a long tongue; it therefore makes use of a twig, held in its beak, to extract insects from bark (Speakley, 1989).

If all the 14 species had been created separately, why are they all finches? If a woodpecker would serve as a woodpecker in the rest of the world, why should it be a finch that acts as a woodpecker on the Galapagos? But the facts makre sense if the species all evolved from a common ancestor. If a single finch colonized the Galapagos and then speciated into the present 14 forms, we should expect them all to be finches: they all descended from a finch. The fact that they are finches is known from the homologies that define a finch. If they had been created separately, we should not expect them to share all th finch-homologies. The woodpecker would be the same woodpecker as anywhere else in the world; it would not have finch-defining traits. The Galapagos finches, therefore, provide evidence of evolution.

We now come to the final argument for evolution: the fossil record. The fossil record offers two candidate arguments for evolution. One is the direct of evolutionary change over geological time. Because geological time lasts longer than the life of any human being, we might hope that he fossil record would show more extensive evolutionary change than those cases of directly observed evolution that we have dealt with. The second kind of of geological argument steps back from observations of single evolutionary lineages to consider the pattern of the fossil record as a whole. This leads to the argument from what Darwin called -in a chapter title- "The Geological succession of Organic Beings". Let us consider the two in turn.

The fossil record of evolutionary change within single evolutionary lineages is very poor. If evolution is true, species originate through changes of ancestral species: one might expect to be able to see this in the fossil record. In fact it can rarely be seen. In 1859 Darwin could not cite a single example. He attributed the absence of examples to the incompleteness of the fossil record (cf. Mendelejeff's account on the elements' table). Thus the chapter of the Origin of Species in which he considers this first geological argument is entitled 'On the Imperfections of the Geological Record'. There are now some cases in which evolutionary change can be seen in the fossil record. A few dozen could be listed. But the most striking thing about them is their rarity. This being so, the first geological argument cannot provide a strong plea for evolution. With the accumulation of evidence it may become a powerful argument; but at present it is not. Nor, of course, is the rarity of observable evolution in the fossil record an argument against evolution. That rarity is exactly what an evolutionist would expect if the fosssil record contained many gaps: and it is known that the fossil record is very incomplete.

The second geological argument is more successful. For this argument we retreat from the evolutionary change of single lineages to look instead at the distribution of the main animal groups in time. Take the vertebrates as an example. Fish first appear in the fossil record before amphibians, amphibians appear before reptiles, reptiles appear before mammals, with a clear sequence of progressively more mammal-like reptiles, in the right order, in between; the first mammals appear before the smaller subgroups of mammals, such as apes; humans appear only a million of years ago. This sequence is exactly what the theory of evolution predicts. In order for a mammal to evolve from a fish it would have to go through amphibian, then reptilian, and the mammal-like reptilian stages; the evolutionist therefore expects these groups to appear in the fossil record in the order they do. Conversely, he would be very worried if they appeared in some other order. The pattern of geological succession, as a whole, fits evolution quite well.

It does no fit the theory of separate creation. If fish, amphibians, reptiles, mammal-like reptiles, and mammals had been created separately, it would be too great a coincidence that they should appear in the fossil record in exactly the order predicted by evolution. If mammals and fish had separate but contemporary origins, why are no mammals at all found in the fossil record as early as fish? There is one possible reason. Something like the theory of separate creation was held at one time by Charles Lyell. Lyell was a geologist, well aware of the pattern of the geological succession. He tried to reconcile it with separate creation by arguing that the groups that were common at a particular time were those favoured by the prevailing environmental conditions. Changes in which groups were common -he supposed- were caused by changes in the environment. Thus amphibians came after fish because the environment so changed as to enable amphibians to become relatively more abundant, and therefore relatively more likely to leave a fossil record.

Lyell's explanation of the geological succesion might stand up if the geological succession were the only argument for evolution (Leakey, 1977). It is a forced argument, but difficult to refute decisively. The main reason for supposing that Lyell was wrong -and it is the reason why he himself changed his mind in the 1860s- is that we have abundant other reasons for supposing that evolution, rather than separate creation is true. Once we accept evolution we can abandon Lyell's forced argument more confidently. The geological succession fits the theory of evolution.

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