The
UNEXPLAINED
Mysteries of Mind Space and Time
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The
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Does the neo-Darwinian theory of natural selection really conflict with the biblical account of creation? Can it account for the astonishing variety of living things? RUPERT SHELDRAKE examines the arguments THE THEORY OF EVOLUTION, in its most general terms, states that new species of plants and animals are descended from species that existed before them. This is what used to be called the theory of descent, or transformism. It was widely known and discussed for two generations before Charles Darwin published his Origin of species in 1859; indeed, one version was proposed by his grandfather, Erasmus Darwin, in 1794; another was put forward by the French scientist Jean Baptiste Lamarck in 1809. Darwin's theory conflicted with the view of the leading philosophers of the ancient world, most notably Aristotle, that species were eternally fixed and unchangeable. In the light of this classical philosophy, the biblical account of creation in the book of Genesis was interpreted to mean that God directly created all the different species of plants and animals, and that they remained unchanged thereafter. The theory of evolution by descent was opposed throughout the 19th century - and is still opposed - by biblical fundamentalists. However, among scientists it has been widely accepted for decades, and is generally taken for granted. But to accept that species have evolved from other species - what is often referred to as the 'fact' of evolution - raises the questions of why species should have changed, and of how they do so. This is an area of much controversy within science. In his famous book, whose full title was On the origin of species by means of natural selection, or the preservation of favoured races in the struggle for life, Charles Darwin put forward a particular theory of the way in which evolution occurred. In doing so, he made the notion of evolution by descent much more credible than it had been before, because he was able to suggest a plausible mechanism - natural selection - for the transformation of species. Thenceforth the general theory of evolution by descent and Darwin's theory of natural selection became closely associated with each other. However, it is important to realise that it is possible to accept the idea of evolution without accepting Darwin's explanation of it. Although the arguments for evolution are well-known, it seems worth reminding ourselves of them. The first depends on the fossil record, in which the remains ofvast numbers of animals and plants are preserved, often in layers that indicate the sequence in which they were laid down. These fossils show that many of the different kinds of animals and plants that once existed on the Earth have become extinct. The best-known are the giant reptiles, such as the dinosaurs, which died out about 70 million years ago.
Since in many cases new types of organism resemble ones that existed before them, it is reasonable to suppose that they were descended from pre-existing species. For example, the birds and mammals appeared long after the reptiles had become established, and share many anatomical features, such as having two pairs of limbs with five digits at the end, which in spite of their different modifications in the wings of birds, fingers of men, and flippers of whales, show a common underlying pattern. The second reason for thinking that evolution occurs is provided by the many different breeds and varieties of domesticated animals and plants. Think for example, of the differences between dogs such as grey-hounds and Pekinese. The fact that these have been produced by selective breeding from similar ancestral stock shows that the form of the species is not rigidly fixed, but can change with time. Thirdly, the geographical distribution of certain species of plants and animals suggests that they have evolved by descent. An example that greatly impressed Darwin was that of the finches native to the Galapagos Islands, off the coast of South America. Distinct species, adapted to different methods of feeding, occur on these islands within short distances, while on the mainland there are closely related finches. The simplest explanation of these facts is that a few finches migrated from the mainland to the islands, and that some of their descendants evolved into new species adapted to the local conditions. Many other similar examples have been described.
Lastly, the fact that animals and plants can be grouped together in hierarchical systems of classification supports the notion of descent. For instance, the human species is grouped with the primates, together with monkeys and apes; the primates are grouped with other mammals; and the mammals with other vertebrates. The similarities within each group are most easily explained in terms of descent from common ancestors; the bigger the grouping, the more remote the ancestral links. The only alternative to the evolutionary interpretation of the evidence is to suppose that species were specially created from nonliving matter at frequent intervals over a long period of time, in such a way that new species resembled species that had been created before them, and in the same geographical areas. This seems extremely implausible, but some people feel bound to adopt this theory in an attempt to harmonise the factual evidence with one particular interpretation of the accounts of creation in the book of Genesis. But this is completely unnecessary, even for those who accept the authority ofthe Bible. In fact, there is surprisingly little conflict between modern scientific theories of the development of the Universe and the sequence of events described in the first chapter of Genesis. The Universe is generally supposed by physicists to have originated with an enormous primordial explosion. As the Universe began to cool down after this 'big bang', matter in the form of atoms condensed from the incandescent plasma, and vast gas clouds gave rise to galaxies of stars. Relatively small bodies of hot matter were then captured by the gravitational pull of the stars and became planets orbiting around them. One such was the Earth. As the Earth cooled, the water vapour condensed and gave rise to the seas. Life originated in the water, and among the earliest living organisms were plants capable of photosynthesis. Animals arose first in the sea, and later colonised the dry land. From these land animals in the fullness of time, Man evolved.
The first chapter of Genesis describes a similar sequence: first the separation of light from darkness - or in other words, of radiation from matter. Then the separation of the Earth as a single mass from the heavens, and the subsequent appearance of the seas and dry land. Then the origin of plants, then of animals in the sea, then of land animals, and finally of Man. These two descriptions of the origins of things differ in that the scientific one supposes that the time scale was of thousands of millions of years, whereas the Bible speaks of the different stages as taking place on different days. If the term 'day' is interpreted to mean an age, there need be little conflict between the two accounts. The main discrepancy is that in Genesis, the Sun and Moon appear only on the fourth 'day'. But this in itself is significant in that it shows that the term 'day' is not to be taken literally, for it could not possibly have a literal meaning if the Sun, by the rising or setting of which days are measured, did not yet exist, according to the very same text. Moreover, other passages in the Bible make it perfectly plain that human measurements of time are not the same as divine ones. 'One day is with the Lord as a thousand years, and a thousand years as one day.' In the end, it seems that the protracted controversy between biblical fundamentalists and evolutionists, so often portrayed as a dramatic confrontation of science and religion, comes down to little more than a dispute over the meaning of the word 'day' in a context that provides no basis for assuming that a day must consist of 24 hours. Thus there seem to be no good grounds, even-religious ones, for rejecting the theory of evolution by descent. However, a new series of controversies springs up as soon as we accept this theory. Once again, underlying many of them are religious and philosophical questions, although on the surface they may seem to be purely scientific.
The most important of these controversies concerns the Origin of new species: do they come into being gradually, or as a result of sudden 'sports' or jumps? This question has been hotly debated for over a hundred years. The two schools of thought are usually referred to as gradualism and punctuationalism. Darwin himself was a gradualist, and so are his modern followers, the neo-Darwinians. Their reasons for adopting this point of view are more philosophical than scientific. Even before the publication of Origin of species, several writers pointed out that the theory of evolution did not contradict the idea of the creation of species by God, because God might just as well make a new species by transforming an existing one as by forming it directly from non-living matter. On this view, the Creator was continually guiding the evolutionary process and making new species through it. One advantage of this interpretation was that it supplied a ready explanation for the relatively sudden appearance of new kinds of animals and plants. On the other hand, those who espoused the philosophy of materialism had to try to explain the process of evolution in terms of the laws of matter alone, and were at pains to reject anything that smacked of the miraculous. Darwin himself favoured gradualism because of his materialist presuppositions, and rejected the idea of sudden changes because, as he wrote in Origin of species, it seems to me to enter into the realms of miracle, and to leave those of science'.
Although such philosophical views have continued to play a hidden but important role in the debate, there is no real reason for the belief in a Creator to lead to a denial of the gradual evolution of new species, or on the other hand for a materialist to deny sudden jumps in evolution. Surprisingly the two concepts can be reconciled. There are in fact theologians who argue that God created the different forms of life by setting up the Universe and the laws of nature, including the possibility of random genetic change, in the first place in such a way that evolution was bound to occur exactly as neo-Darwinians think it does. By contrast, some materialists accept the idea of sudden large changes, but regard them as random.
Now, leaving aside these philosophical questions, we can turn to the factual evidence concerning the origin of new species. The main argument used bv Darwin in favour of gradualism relied on an analogy with the development of breeds of domesticated animals, such as dogs, pigeons and rabbits, and varieties of cultivated plants, such as cabbages, dahlias and grapes, by the agency of human selection. He reasoned that just as animal and plant breeders select favourable specimens as parents of the next generation, and thus gradually improve the breed or variety in a particular direction, so in the wild natural selection would result in parents well-adapted to the conditions of life leaving more offspring than those less well-adapted. There would thus be a progressive improvement in the adaptation of the race to its environment. However, the controversial question is not how locally adapted races arise within species, but how species themselves originate. Ironically, this is the very question that Darwin failed to answer satisfactorily in Origin of species. He simply assumed, as his followers also assume, that the same kinds of process continued over long periods of time would lead to the gradual divergence of races into new species. No one disputes that this may sometimes occur, but the opponents of gradualism claim that many, if not most, species arise much more quickly, by relatively large and sudden transformations.
This case, like Darwin's own, can be based on an analogy with the breeding of domesticated animals and plants. For while some new varieties or strains have been produced gradually by long-continued selection, others have originated suddenly from occasional 'sports' or freaks. In fruit trees, for example, peculiar shoots sometimes appear, differing from all the others, from which new varieties can be propagated. In the history of animal breeding too, new breeds have been started from spontaneously occurring freaks.
If in the course of evolution, freaks or sports produced by wild animals and plants occasionally survived and managed to breed successfully, a distinct new type derived from the original species could come into existence more or less suddenly. For example, it seems probable that a fossil rhino genus called Teleoceras originated in this way. These dwarf, short-legged rhinos resemble ancon sheep and, like them, may have appeared suddenly as a result of a genetic mutation leading to the improper development of cartilage at the end of bones, a condition known as achondroplasia. If this were so, we would not expect to find in the fossil record a whole range of intermediate types between Teleoceras and the rhino species from which it evolved. No missing links have been found. As a general rule, in the fossil record new species appear, continue relatively unchanged for maybe several million years, and then become extinct. There is little evidence to support the gradualist view. Darwin argued that this was due to the imperfection of the fossil record, but after 120 years of further research, this argument is wearing rather thin. Furthermore, calculations of the rates of evolutionary change, based on data from fossil horses and other groups of animals, have shown that they are much too slow to be able to account for the gradual appearance of all the different kinds of organisms in the time available, long though it has been. The neo-Darwinians reply that gradual changes might have been much less slow at some periods than others. But in admitting this, they shift their position so that it comes much closer to the idea of discontinuous or sudden changes.
Hopeful monsters Those who advocate sudden jumps in evolution do not deny that the great majority of freakish organisms will be weeded out by natural selection. On the long time scale of evolution, it is sufficient that only very rarely are 'hopeful monsters' able to survive and reproduce. Even neo-Darwinians can hardly deny that this might have happened. The two schools of thought differ mainly in their emphasis, one considering that sudden jumps have played little part in the evolution of new species and the other claiming that many, if not most, new types have arisen in this way. On balance, the available evidence supports the second of these views, although a great deal of work remains to be done. This is what the current controversy among evolutionary theorists is all about. At first sight it is puzzling that these issues should raise such passionate feelings. But as in earlier controversies, some of the contenders are fighting to defend not just scientific theories but their fundamental beliefs. This time, however, it is the materialists who feel threatened by the challenge to orthodoxy.
What are the limitations of the neo-Darwinian theory of evolution? See page 1214
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Reproduced from THE UNEXPLAINED p1161
One of the most convincing reasons for thinking that sudden
jumps occur is that many present-day species differ from more or less closely
related species in the number and structure of their chromosomes. Changes
in chromosomes of these types are known to occur occasionally during the
process of cell division, known as meiosis, that produces egg and sperm cells.
The chromosomes of the mother cell come together in pairs at the beginning
of meiosis, and normally one of each pair then moves into each of the two
daughter cells. But sometimes pairs fail to separate properly, and one daughter
cell gets too many chromosomes, and the other too few. Consequently offspring
derived from these abnormal cells have the wrong number of chromosomes. They
are often both abnormal and sterile as a consequence; but if they do manage
to breed, either through self-fertilisation, as commonly occurs in plants,
or by crossing with similarly abnormal organisms (their own brothers or sisters,
for instance), they may give rise to a new species straight away; the differences
in chromosome numbers set up barriers to interbreeding and keep the new type
separate from the parent species. Other chromosomal changes during meiosis
involving the breaking and rejoining of chromosomes in the wrong places can
have a similar effect.