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Evolution Toward What?

The Beagle Record: Selections from the Original Pictorial Records and Written Accounts of the Voyage of H.M.S. Beagle

edited by Richard Darwin Keynes
Cambridge University Press, 409 pp., $75.00

Darwin and the Beagle

by Alan Moorehead
Penguin Books, 224 pp., $9.95 (paper)

Charles Darwin and the Problem of Creation

by Neal C. Gillespie
University of Chicago Press, 202 pp., $16.50

The Darwinian Revolution

by Michael Ruse
University of Chicago Press, 320 pp., $20.00

Somatic Selection and Adaptive Evolution

by E. J. Steele
Williams and Wallace International (Toronto), 91 pp., $14.95

Patterns of Evolution

edited by Arthur Hallam
Elsevier, 592 pp., $83.00

It is interesting that the scientific discovery that has had the greatest influence on human thought has no practical use whatever. Darwin’s demonstration that there was a time when no men existed and that we are directly descended from animals provided a whole set of new problems about the nature and limitations of religion, philosophy, and science. Yet the history of the origins of the new science of biology is still not fully understood. Did it grow out of the earlier sciences? Are we sure even today that it is an exact science, conforming to the same principles as the others? The progress of astronomy, physics, and chemistry has been charted through the centuries. But biology is a subject so recent and yet so extensive that we find it hard to see when it started or indeed where it begins and ends today. All thinking depends on the brain, so can there be boundaries between philosophy and biology? Conversely all living things consist of molecules, so does the study of life derive its fundamental principles from those of physics and chemistry? Some biologists enthusiastically say “Yes,” while others revile them as “reductionists.” Such thoughts lead us to basic metaphysical problems about whether there are fundamental laws of the universe and if so how much can human beings know about them.

These were questions that were being discussed before Darwin, as the books under review amply show. Evidence that evolution has occurred did not answer them, indeed made them more acute by blurring the old distinctions between man and the rest of nature. The growth of knowledge since then has made it quite certain that evolution has occurred and we now have some insights into its nature. It is often said that evolution has no direction, but it seems to me that the understanding that we now have of living processes shows clearly that the striving of organisms to maintain their improbable state has been the cause of an overall change that can be called progressive. The evidence for this comes from many sources. Knowledge of the repeated changes of ancient climates explains why so many creatures have become extinct. Others have then been stimulated by the new conditions to acquire fresh information that has allowed them to survive. As a result there has been, over the years, an increase in living things of information and complexity of structure and behavior.

It is true that molecular biologists have raised new problems about evolution and their focus on mutation has led to emphasis on what Jacques Monod has called Chance and Necessity. These biochemical workers are very ingenious but they should not be allowed the last word about evolution. They mostly work with bacteria and the nature of their methods forces them to consider single substances, or few of them, such as DNA or proteins. Biologists and paleontologists who study the lives of whole complicated creatures, living and extinct, emphasize other factors besides chance, and they nearly all find evidence of progress in evolution. As the Harvard ornithologist Ernst Mayr puts it, “If we study the record of life on earth from its very beginning we do note a progression.”

The nature of the evolutionary process is thus still actively debated today. It is interesting to compare the themes that we are arguing about with those that were discussed before and after Darwin’s great contribution in 1859. The Beagle Record is especially valuable for giving a fresh view of the conditions under which the foundations for that contribution were laid. Richard Keynes is Darwin’s great grandson, now professor of physiology at Cambridge. He has been several times to South America to study how electric eels produce their shocks and while in Buenos Aires in 1968 he was shown the sketchbooks of Conrad Martens, who was for some months the artist on the voyage of the Beagle. They include beautiful pictures of the places the ship visited and this gave Keynes the idea of weaving around them the book under review. He has made a very happy selection from Darwin’s own account in his autobiography and notebooks and letters. Interspersed with these are pieces from the Narrative of the voyage written by Captain FitzRoy after the return and not republished since 1839 (except for a selection by Stanbury for the Folio Society in 1977). Even more interesting are some letters written by FitzRoy and never published before. The result, excellently produced by the Cambridge University Press, is a truly marvelous book, which will please both scholars and laymen. Besides retelling this famous story it provides a fascinating account of the relations of two able men, with very different characters.

Alan Moorehead’s book on the Beagle voyage, first published in 1969 at the time of his successful film treatment of the voyage, has recently been republished. The text is here all his own, as readable and indeed as “graphic” as the illustrations themselves.

Of course we need more than the words of the participants if we are to understand the significance of Darwin’s work. Michael Ruse and Neal Gillespie both deal with the thought of the period, Ruse more as a historian, Gillespie as a philosopher. Ruse uses as his subtitle “Science Red in Tooth and Claw,” which suggests something of his tone and style, though luckily the book itself has little to say on that theme. He presents the intellectual issues raised by Darwin in the setting of society and science in nineteenth-century Britain. He points out that Darwin’s was a characteristically British discovery and discusses why it was only slowly taken up on the Continent and in America. Unfortunately his attempt to give the essence of men’s thoughts in modern terms can seem naïve. “Lamarck tried hard to be a good materialist” evokes a smile. That Darwin “by the time he left Cambridge…determined to seek a place in Science” is a statement that needs documentation and does not get it. Incidentally neither Ruse nor Gillespie emphasizes sufficiently that what moved Darwin was mainly his intense interest and pleasure in the study of living things.

Ruse successfully introduces us to characters and ideas that influenced Darwin. There were many earlier suggestions that species had been transformed, and theories on how this might have occurred. The geologist Lyell, for instance, whose work Darwin followed closely, discussed how species became extinct as the result of a “struggle for existence” in which “all the plants of a given country are at war with one another.” Darwin had plenty of suggestions to work with even before, in 1838, he came upon the ideas of overpopulation first published by Malthus in 1798. Indeed in 1844 a detailed exposition of evolution appeared in The Vestiges of the Natural History of Creation, written by Robert Chambers, though published anonymously. Ruse discusses carefully how Darwin’s facts and the changing climate of ideas ensured that the Origin convinced people of evolution in 1859 after so many had previously failed to do so.

Every generation defines its problems in a different way. Historians of science have used various techniques to express this process of continuous change of ideas. In tracing the origin of modern views of evolution Gillespie uses the concepts of “epistemes” as postulated by the French philosopher Foucault and the “paradigms” of the American Thomas Kuhn. Foucault believes that “In any given culture and at any given moment there is always only one episteme that defines the conditions of possibility of all knowledge.” Gillespie in effect denies the truth of this position since he claims that in the period before Darwin there were two major epistemes, which he calls creationism and positivism. Creationists believed in the intervention of God in the affairs of the world at its beginning, and perhaps still today. Positivists “saw the purpose of science to be the discovery of laws which reflected the operation of purely natural or ‘secondary’ causes.”

Foucault would presumably say that there cannot be two epistemes, and indeed these two views are more like Kuhn’s paradigms. Whatever we call them they are still with us today. It is dangerously easy to forget that there are many, many millions of people who still believe in miraculous interventions. In spite of what rational theologians argue about “myths” simple people still expect miracles, and religious and political leaders are only too happy to promise them. Luckily it is not common to find scientists believing in such superstitions, though some come pretty close to it.

Biologists have very good evidence for believing that animals and plants have arrived at the present state by some form of gradual change under the influence of “natural” causes. Indeed we know for certain that evolution goes on steadily every day, for instance as pests and parasites become resistant to the drugs we invent to destroy them. Yet several of the questions about natural selection that worried people in the last century are still not settled. Scientists for example have very different views on rates of evolution; there is evidence that at some periods it was not gradual at all, but very rapid. This almost takes us back to the idea—popular during the nineteenth century—that a series of catastrophes took place, of which the last was the biblical flood. Most biologists today. having little historical sense, think of the theory of catastrophes as an absurd biblical literalism. The books by Ruse and Gillespie both explain (as is already well known) that the theory had various forms and was a serious attempt to explain the known succession of geological strata. What Ruse and Gillespie have not noticed is that recent evidence now suggests that there have indeed been quite catastrophic revolutions in animal and plant life.

It has long been known that there have been times when animals and plants changed drastically. Geologists divided up the earth’s history into periods because they saw such sharp breaks. The best known of them was at the end of the Cretaceous period, when the giant reptiles disappeared and the mammals began their great increase. It is estimated that at that time three quarters of all the species of animals and plants became extinct, which is more extinctions than would be expected if half the world’s stockpile of nuclear weapons exlpoded. It was especially the large animals that disappeared, whereas the small lizards and shrew-like mammals survived.

What killed off the giants? Evidence from the cores of deposits recovered from the sea floors by the Deep Sea Drilling Project allow us to determine the climate in ancient times from the proportion of the isotopes of oxygen in the skeletons of the fossils. This shows that at the end of the Cretaceous period there was a sudden world-wide fall of temperature, followed by an equally rapid rise. Both changes may have been too quick to allow adjustment by organisms that had become accustomed to the relatively stable warm conditions of Cretaceous. The exact times taken for these changes are still uncertain but were undoubtedly short by geological standards (less than half a million years) and may have been much shorter, even as little as 100 years. Even more dramatic is the suggestion by the Canadian paleobiologist Russell that the extinction of so many large animals might have been caused by the explosion of a supernova. These are colossal stellar expansions which for about two weeks, radiate as much energy as ten billion suns. They occur about once every fifty years per galaxy. This means that one may occur every seventy million years close enough to affect the earth. It could therefore explain the extinctions, for the large animals would have been more susceptible to radiation damage.

Nearer to our own time there have been almost equally rapid extinctions. Some scientists believe that the composition of borings of arctic ice shows that there was a period about 100,000 years ago when the climate changed from glacial to as warm as today in only 100 years. Not everyone accepts these extreme figures, but all geologists agree that there have been rapid and repeated changes of climate. Paleontologists who study the fossils find corresponding evidence of repeated massive extinctions of species of animals and plants and their replacements by new ones.

So both paleontology and paleoclimatology suggest that there have been catastrophic changes in the past and presumably will be again in the future. Some of these changes have been rhythmic, in relation to cycles of sunspots and changes in the earth’s orbit, and these can be forecast. The really large and rapid changes may depend upon the properties of galaxies and here we come near to the limits of our knowledge. If there is a possibility of bursts of radiation that might make large creatures like ourselves extinct we should very much like to be able to forecast them. Discussion of whether they are the product of detectable laws of nature becomes much more than academic.

Darwin would certainly have rejoiced at all the recent evidence about change. He postulated that the continual adaptation to new circumstances depended on selection among the many varied individuals within each species. I think that he would therefore also have welcomed the facts that molecular biologists bring to this controversy, though they themselves are often non-selectionists. They find that many of the molecules in the body can exist in numerous slightly different forms, each determined by heredity. Your enzymes and mine differ as much as our faces. The biochemists find it difficult to believe that all of the genes responsible for these differences have been preserved by natural selection. But Darwin’s point was precisely that it is the presence of this great variability that makes adaptation by natural selection possible. The slight difference in action of almost identical enzymes may provide the basis for the evolution of all the marvelous complexities of the body.

Some biologists such as Stephen Jay Gould and Richard Lewontin of Harvard have rightly protested that this does not mean that all variations are necessarily valuable.* We can go too far in trying to find “adaptive significance” in every feature of every plant or animal. The American mathematical biologist Sewall Wright has long claimed that in small communities evolutionary change may proceed by chance, the process known as “genetic drift.” If two such drifting populations of a species remain separate for long enough they may come to differ so greatly as to be unable to breed. Geographical barriers are thus probably very important agents in the origin of new species.

Even though chance plays a part, animals and plants can survive only by adequate response to environmental conditions. The continuity of life in a changing world depends on the presence of many slightly different creatures of each sort. The most complex organs, such as the eye, have been developed by the selection of many small variants of each feature of them. This process of selection among a huge number of infinitely small variables can also explain the correlated evolution of different parts of the body—the giraffe’s long neck can only be useful if he has a heart that can pump blood up it to his brain and so on. Nature’s way of meeting future contingencies is to provide infinitely many creatures with small differences.

Some people find it difficult to believe that this procedure can be effective, perhaps because it is so very different from the methods of careful designing that we use today to make our machines (though earlier procedures were more like nature’s). The desire to find some other mechanism than natural selection is certainly strong, and to some people it seems obvious that the more rapid adaptations to circumstances produced by change during the lifetime of the individual must be passed on.

This is the Lamarckian view, that acquired characters are inherited. E.J. Steele is a Canadian immunologist who has, as he says, “stuck his neck out” to present a modern version of Lamarck, suggesting how the cells of the body might send information to the eggs and sperms to be passed on to the next generation. Darwin himself of course felt the need for just such a mechanism. He hesitatingly suggested the hypothesis of pangenesis, “though I very much fear it will appear to everyone far too speculative,” as he puts it in a letter to Fritz Muller. Steele’s speculation is that the carriers of information from the body cells to the germ cells are like the so-called C-type RNA viruses. They are able to “capture” the genes of one cell and then go on to infect another one.

This is indeed an ingenious idea and it has appealed so strongly to Karl Popper that he recently chose Steele’s book as his favorite among those published during the last year. I doubt whether biologists will be so ready to join in reviving Lamarckism. Apart from everything else they will remember that the erroneous theories of Lysenko had disastrous effects on agriculture in Russia. A serious reason for doubting Steele’s theory is that it is based on the behavior of clones of cells, that is to say sets that are dividing continuously, as do those of the bone marrow or the skin. But the chief bearers of experience and learning that we want to pass on to our children are the nerve cells, and they never divide, they do not form clones. Steele admits this and tries to get around it, but neurologists will not easily be convinced. Still, the discovery of transfer by viruses is one of the unexpected facts that remind biologists how much there is they do not know.

Of course the capacity to learn or to adapt the tissues during a lifetime is one of the chief aids to survival and genes that promote it are likely to be selected. But such adaptation is not a matter of “chance.” The whole individual must strive if its learning and adaptive powers are to be effective. We hear far too much nowadays about the chance factor in evolution. Genetic drift indeed probably occurs, but Sewall Wright never claimed that it could explain the adaptations of living things, which must depend upon selection of heritable variations. Change of genes by mutation is certainly a matter of the chance effects of radiation and other factors. But the power to adapt does not have to wait upon the accident of mutation. All species contain vast reserves of variation that can be called upon by sufficiently strong efforts to survive. Of course the capacity to make such effort is itself genetically variable. The manifestation of every characteristic is, as I have put it elsewhere, “double dependent,” partly on heredity, partly on the influence of the surroundings. Many controversies would be avoided if people realized that all characteristics show double dependence.

Of all the “eternal questions,” as Stephen Jay Gould called them, that have been asked about evolution the most fascinating is whether there has been a discernible progress. The answers given by those who should be qualified to know can be seen in a set of essays by seventeen scientists collected by Professor Arthur Hallam of Birmingham in England. It is striking that most of the authors detect some direction in the changes that have occurred. “We have evidence of an upward spiral of efficiency within the Cenozoic Mammals both for locomotory adaptations and for intelligence.” Of course this leaves open the question of what we mean by “efficiency.” Throughout the evolution of each group of animals there have been wholesale extinctions and replacements. Does this mean simply that the same environment is occupied by successively more and more “efficient” animals? This partly depends on the difficult question of what is meant by “the same environment.”

Still, the evidence, taken together, is that there has been an increase in the total amount and variety of life on earth. Competition, variation, and effort have ensured that animals and plants have continually colonized new niches, for instance when first plants then fishes came on land, and insects and birds took to the air. Each new habitat puts different demands on the organism of the creature, which can be met only by new devices. Roots or legs or wings are the product of new information, encoded in the genes. Inherited information is what differentiates living from lifeless matter and increase of information is the real sign of progress in evolution. The higher organisms can do more different things than their ancestors because they inherit more information. Moreover they can learn with their sense organs and brains how to improve still further their responses to the environment.

The basic aim of every living thing to strive to find how to survive has thus led to a steady accumulation through the ages of information on how to live better. Human beings have greater powers of accumulating such knowledge than any other animals. I conclude that Darwin’s theory of evolution did not deprive man of his place at the center of creation, at least on earth. Proper consideration of the evidence of those who have fully studied past and present life fully validates our belief that we do indeed have the honor, privilege, and responsibility of being in that position.

Letters

Sewall Wright’s ‘Evolution’ May 1, 1980

News about Darwin March 6, 1980

  1. *

    See for instance R.C. Lewontin, “Adaptation,” in Evolution: A Scientific American Book (W.H. Freeman, 1978).

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