On the Origin of Evolution; Tracing “Darwin’s Dangerous Idea” from Aristotle to DNA

by Paul Braterman

On the Origin of Evolution, John and Mary Gribbin, William Collins, November 2020; HB, pp 267, £20

I thoroughly enjoyed this book. The authors have read widely and deeply over an enormous range of topics, and blended their insights into a coherent unified account covering subjects as diverse as genetics, stratigraphy, and the fine details of chemical bonding. The result is an overview stretching from ancient foreshadowings, through Enlightenment era explorations, to the crucial developments of the mid-19th and early 20th-centuries, which gave us evolution science in something very close to its present form, and beyond that to the 20th-century discoveries of the molecular basis of inheritance, and the more recent discoveries made possible by genome sequencing. Throughout, complex topics are clearly explained to a high level of technical accuracy, without oversimplification or obscurantism. The work is enlivened throughout with well-judged quotations from the scientists involved in these discoveries, including contributions often overlooked. I found two small errors1, but these are of no importance to the narrative. I also had problems with the title and emphasis of the final chapter, The New Lamarkism; more on this later.

The authors will already be familiar to many readers. John Gribbin holds a Ph.D. in astrophysics from Cambridge, where he was part of Fred Hoyle’s research group. He is a prolific and highly successful writer on scientific topics, with In Search of Schrodinger’s Cat and its successor, Schrödinger’s Kittens and the Search for Reality among his best-known works. He and his wife Mary are both Visiting Fellows at the University of Sussex, and have written several books together regarding the history of science, including The Fellowship and Out of the Shadow of a Giant. Those last two both feature Robert Boyle and Robert Hooke, who also make short appearances here.

Evolution is a fact. Those are the, to me, very welcome first words of the Introduction. Later in the paragraph, the authors state their view that the most successful theory of evolution is that of natural selection. I prefer to refer to our understanding of evolution, avoiding the blanket expression “theory of evolution” altogether. This is not just because the word “theory” can bring with it a suggestion of uncertainty, but because there are many partial theories, including notably neutral drift in addition to natural selection, and because evolution intersects with so many other different topics, as the book itself makes clear, from molecular biology to Earth sciences.

The book’s first section, Ancient Times, begins with a historical survey of thinking about evolution from antiquity through the early 19th century, and then pauses to explain how the emerging science of geology provided the authors call “the gift of time”. The second section, The Middle Ages, is devoted to 19th-century developments, pivoting inevitably around Charles Darwin, while the concluding section, Modern Times, is concerned with the emergence of our current perspective, from Mendelian genetics through the elucidation of the structure and function of DNA to such recent developments as horizontal gene transfer, and epigenetics. Space does not permit a full discussion here of all these topics, but I will pick out a few that aroused my personal interest.

The authors explain the importance of deep time as a precondition for evolution, and how William Thomson, Lord Kelvin, argued against this. If anything, they underestimate Kelvin’s theologically motivated opposition. As Birchfield has described,2 Kelvin returned repeatedly to the problem of the age of the Earth as a habitable planet, from his student days until shortly before his death. His earliest estimates were based on the rate of cooling of the Earth but his strongest argument, presented here, was based on the age of the Sun. The largest possible source of energy then known was gravitational infall, and if we divide the total amount of energy available from this source by the amount it emits every year, we end up with an estimate of its maximum possible age. Using this argument, Kelvin (who of course could not possibly have known of the processes of nuclear fusion by which the Sun replenishes its energy) whittled away at geological time, coming to a final estimate of around 20 million years.

Darwin and Wallace were anticipated to a remarkable extent by the Appendix that Patrick Matthew had included in his 1831 volume, On Naval Timber and Arboriculture. The authors quote this to show that Matthew had fully appreciated the importance of competition for resources, and the role of natural selection in driving what we now call evolutionary change. This sent me back to the original work, available here, and I was surprised to find that it showed even more insight than I could have imagined. Thus Matthew begins his appendix by noting the absence of a clear boundary between “varieties” and “species”. He points to the fossil record as evidence of change, rejecting as implausible the only alternative, Cuvier’s doctrine of extinctions followed by repeated acts of creation. Like Darwin, he invokes the effectiveness of selective breeding to show what he calls the “plastic quality” of life, and contrasts the shortness of the historical record with the much longer periods necessary to account for geological formations. Matthew speaks of

the diverging ramifications of the living principle under modification of circumstance

[emphasis in original], says that

the progeny of the same parents, under great difference of circumstance, might, in several generations, even become distinct species, incapable of co-reproduction

and asserts, in language that almost anticipates the closing paragraphs of Origins, that

There is more beauty and unity of design in this continual balancing of life to circumstance, and greater conformity to those dispositions of nature which are manifest to us, than in total destruction and new creation.

Batesian mimicry. Rows 1 and 3 mimics (Dismorphia), rows 2 and 4, the species being mimicked. From Henry Walter Bates 1862. Contributions to an insect fauna of the Amazon Valley. Lepidoptera: Heliconidae. Trans. Linn. Soc. 23: 495-566, via Wikipedia

I particularly appreciated the discussion of Alfred Russel Wallace, the detailed retracing of his pathway, and the case presented for giving pride of place to his observations of tiger beetles, so called because of their hunting habits. On the sands of Sarawak, these were white, but on the mud of Macassar they were so well camouflaged by their brown colour that he could only detect them by their moving shadows. It was interesting to learn that he was a close colleague of Henry Bates, still remembered for describing Batesian mimicry, in which one perhaps harmless species comes to match the warning markings of its dangerous neighbor. The authors point this out as a beautiful example of evolution in action, as increasingly effective mimicry leads to higher levels of protection from predators.

At the centre of the book, we have Wallace’s interactions with Darwin, and the events that led to the joint publication of the theory of evolution by natural selection, which both of them had independently arrived at by a combination of observation and reflection, with in both cases Thomas Malthus’ Essay on Population providing the final link in their chain of thought. In brief, all living things tend to multiply their numbers in successive generations, but this increase cannot be indefinitely sustained because of limited resources, and the inevitable competition gives rise within each species to what Darwin called the struggle for survival. If the individual members of the species vary in any way, and if these variations can be inherited, the inevitable result will be what Herbert Spenser called the “survival of the fittest”, and those variations that enhance the chances of survival and having offspring will be increasingly represented in future generations.

The Wallace Line, discovered by Wallace and named for him by TH Huxley, divides the fauna of Southeast Asia from that of Australasia. Grey represents the extent of land dring the last Ice Age. Altaileopard from pblished sources, via Wikipedia

When, in 1858, Wallace sent in his own description of the principle of natural selection, Darwin’s first impulse was to forward the manuscript to a journal for publication. This may seem strange to us, but at the time this was common practice, unless the author of the material had indicated that he wished it to be regarded as confidential. This, of course, would mean that Darwin had to abandon his own claim to priority, even though he had spelt out this very same theory in his notesand unpublished correspondence in 1844. However, two of Darwin’s close colleagues, Charles Lyell and Joseph Hooker, came up with an ingenious solution. Lyell was the leading figure in British geology at the time, the first volume of his Elements of Geology having be one of the books that Darwin had taken with him on the voyage of the Beagle, a quarter of a century earlier. Hooker was one of Britain’s leading botanists, shortly to become director of Kew Gardens. Between them, they linked extracts of Darwin’s and Wallace’s materials into a single presentation to the Linnaean Society, which they communicated, describing Darwin and Wallace as joint authors, in July 1858. This presentation itself had little impact, until the publication of On the Origin of Species the following year. This book, which has had an influence like few others, had been in the making for many years, and might have stayed that way for many years longer had it not been for the fact that Wallace, all unawares, had forced Darwin’s hand.

Darwin’s detractors claim from time to time that Darwin had somehow cheated Wallace, who was busy collecting in Malaya and what is now Indonesia at the time and unaware of these events. On the contrary. When he returned to the UK and discovered what had happened he was full of gratitude, saying that without the support of such eminent people as Darwin, Wallace, and Hooker his own “sketch” would have remained unnoticed, and if we recall how little attention Matthew’s work had attracted, he may very well have been right. Darwin and Wallace remained friends, although this friendship came under strain when Wallace embraced spiritualism (less of a fringe activity in the 19th century than it is today) and regarded humanity as being something more than the natural product of evolution. When Wallace wrote his own long book about evolution, he called it Darwinism, he was one of Darwin’s pallbearers at his funeral in 1882, and he was still expressing his gratitude to Darwin in 1903.

The idea of evolution was far from new in 1859, although in 1844, when he sent his sketch to Joseph Hooker, Darwin described accepting the mutability of species as “like confessing a murder”. I have long been puzzled as to why he felt this way, given the existence of a long line of evolutionists including his own grandfather, Erasmus Darwin, who had correctly interpreted Linnaeus’ scheme of classification as resulting from shared inheritance. Part of the reason may have been the lack of a mechanism, until the formulation of the principle of natural selection. TH Huxley, who later became one of Darwin’s staunchest supporters, wrote that as late as 1857, he was “inclined to say to both Mosaists [believers in biblical-style separate creation] and Evolutionists, ‘a plague on both your houses!’ “ As he wrote later,

The ‘Origin’… did the immense service of freeing last for ever from the dilemma – refuse to accept the creation hypothesis, and what have you to propose that can be accepted by any cautious reasoner?

Notice the reasoning, made explicit a century later by Lakatos, as I discussed here in an earlier article; a hypothesis will not be rejected, whatever its defects, until a better one becomes available.

Moving on to the section on Modern Times, the authors explain Mendel’s experiments on inheritance in peas, and how they led him to propose the existence of what he called hereditary factors, and we call genes, with different versions of a gene now being known as alleles. Plants, like humans, inherit one version of each gene from each parent. Some features, like human skin colour, depend on many genes, so that parents with different skin colours will tend, on the whole, to have children somewhere in between. But other features, like rough vs smooth skin in peas, are controlled by a single gene. Call the allele that confers rough skin, R, and the allele for smooth skin, S. Plants that are RR or SS will be rough-skinned or smooth-skinned, respectively. However, plants that are genetically mixed, RS, are all smooth-skinned, so S is said to be dominant, while R is described as recessive.  If pollen from an RS parent is used to fertilise an RS plant, then on average one quarter of the offspring will be RR and rough-skinned, one half smooth-skinned because they are RS, and one quarter smooth-skinned because they are SS.3 So in these plants, Mendel observed a smooth to rough ratio of three to one.

A range of fruitfly mutants. Public domain, via Wikipedia

At this point we have a driver for evolution (natural selection), and a mechanism (genetics) to ensure that favoured features can be passed on undiluted and spread through a population. What is still missing is the source for new variations, and this was found early in the 20th century with the discovery of mutations, changes in the nature of a gene resulting, as we would now say, from a copying error. Here the authors describe how Thomas Hunt Morgan observed a white-eyed mutant male among the red-eyed fruit flies that he was studying, and how he showed it to be a sex-linked recessive, like red-green colour blindness in humans. I would have liked to hear more at this point about the role of Hugo de Vries, who had earlier observed mutation in evening primrose plants, and actually coined the term mutation. Mutations provide the raw material for evolution. To use an expression that de Vries borrowed from an admirer of his work, “natural selection may explain the survival of the fittest, but it cannot explain the arrival of the fittest”, and each new variation that conferred additional fitness had arrived through mutation.

Early in the 20th century, de Vries and others regarded mutation theory as antagonistic to Darwinian evolution. Darwin had inherited from Lyell the belief that natural change, whether in geology or in biology, was an intrinsically gradual process. But once we allow change to occur one allele at a time, we can see mutations as providing the raw material for on-going Darwinian evolution, and combining these two perspectives we have in place all the features of what became known as the Modern Synthesis.

The authors go on to describe how it came to be established that the genetic information was encoded in DNA, and bring new insights to the oft-told tale of the elucidation of its structure. On their telling, Rosalind Franklin was indeed treated shabbily in the crucial interlocking publications, on one of which she was an author. However it was not Franklin who was shortchanged by the Nobel committee, since she was in any case ineligible by the time the award was made, being dead, but rather her assistant at Kings College London, Raymond Gosling. The authors do comment however on the Nobel Committee’s ongoing misogyny, as in the case of Martha Chase, denied credit for her share in the work that demonstrated that it was not the protein coat that carried the information in viruses, but their nucleic acid content.

I would add that between 1953, when Franklin left King’s for Birkbeck, and her death in 1958, she established another collaboration that would lead to a Nobel Prize, this time with Aaron Klug on the structure of viruses.

The last chapter of the book is called The New Lamarkism, I dislike this title, for several reasons. The authors incorrectly4 equate epigenetic inheritance with Lamarckism, and epigenetics is just one of the topics covered in this short but stimulating chapter. So here I feel the authors may have been misled by those claiming that the many extensions to the Modern Synthesis (nowadays we talk about the Extended Synthesis, or even the Extended Extended Synthesis) are reshaping of the foundations, rather than rearranging parts of the superstructure. However, the chapter gives an excellent account of the development of the concept of a genetic code, how this code operates, and many other matters.

I take more serious issue with them regarding the role of non-coding DNA, i.e. the DNA that does not directly code for protein. Some part of this DNA certainly has important control functions, but the authors go too far when they say

Of course, this DNA isn’t really useless. The “non-coding” DNA must be doing something – and clearly something important – even if it doesn’t code for protein.

The assumption here seems to be that if this DNA were not useful, evolution would have got rid of it. The argument is plausible, but will not survive what has become known as Gregory’s onion test. T. Ryan Gregory is Chair of the College of Biological Science at the University of Guelph, and Senior Handling Editor of the journal Evolution: Education and Outreach. His onion test points out that the genome of an onion contains roughly 5 times the length of DNA as that of a human. But it is simply not credible that the development of an onion requires five times as much information.  What has happened here is that the authors have fallen prey to what might be called the adaptationist fallacy, the belief that every feature of an organism can be explained in terms of function. This perspective runs through general public understanding, from Darwin’s time onwards, and I was surprised when I learnt that many leading biologists regard it as 50 years or more out of date.

[allium3.jpg]
These species of Allium, relatives of the onion, vary in amount of genetic materia lby a factor of four. Image fromGregory, loc. cit.
The reality would seem to be that most evolution is driven by chance, as explained in 1968 by Mooto Kimura. This, more than selection, explains the formation of new species. When two populations are prevented from interbreeding, for whatever reason, they will simply drift apart. It seems natural to look for the function of any evolved feature – the stripes of the zebra, for example – but first we need to show that there really is a function.

As to why this matters, I would cite the arguments of a 2016 paper by Koonin that I discussed here in 3 Quarks Daily. In justification of their view regarding non-coding DNA in humans, the Gribbins refer to the fact that the amount of such DNA in bacteria is only around 10%, as opposed to some 98% in humans. But there is a simple reason for this.  Unused DNA is indeed a drag on the system, but a very small one. So the selection pressure to get rid of it is also small, and it is only in organisms such as bacteria, which go through a very large number of generations, that this very feeble pressure has had time to take effect. However, complex organisms enjoy an unexpected benefit from their unused DNA, since each portion of this DNA will be able to mutate freely at random, and may thereby chance to develop into something useful, ensuring an ongoing supply of totally new genetic material.  None of this had been foreseen by any of those thinking about inheritance, until, relatively recently, sequencing led to the identification of such “orphan genes”. As Leslie Orgel put it,5 evolution is smarter than we are.

1] The authors follow many others in over-interpreting the extent to which mediaeval Muslim scholars had advanced beyond Aristotle’s Great Chain of Being, and in particular in accepting a widely cited mistranslation of the work of al-Tusi; I have discussed this in Muslim Heritage, reprinted here in 3 Quarks Daily. And they describe purines as containing two fused six-membered rings, whereas in fact one of the rings is five-membered. Also, on p. 218, they include cytosine in their list of purines, but this would seem to be a mere clerical error.

2] Lord Kelvin and they Age of the Earth, Joe D. Burchfield, University of Chicago Press, 1990.

3] We have four equally possible situations; RR, R from pollen and S from ovum and S from pollen and R from ovum, both of which giving what I have listed as RS, and SS.

4] I consulted the philosopher and biologist, Massimo Pigliucci, on this, and he referred me to his on-line publication, https://platofootnote.wordpress.com/2017/09/19/one-more-time-no-epigenetics-is-not-lamarckism/. Lamarck specifically proposed that evolution proceeded through adaptive inheritance by the offspring of what had been achieved by their parents, implying inheritance from the whole organism, rather than specifically from the germ line. Epigenetic inheritance takes place through the germ line, although admittedly this may have been altered by events to which the whole organism has been exposed, and like any other genetic change may or may not be adaptive.

5] Leslie Orgel was one of the leading 20th century investigators of the science related to the origins of life. His actual words were “Evolution is smarter than Leslie Orgel”,  but given how smart Orgel was, that comes to much the same thing.

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