Author Archives: John Wilkins

About John Wilkins

Historian and philosopher of science, especially biology. Apple tragic. Pratchett fan. Curmudgeon.

Book review: Understanding Evolution

I posted this on Panda’s Thumb, but I thought I would repeat it here.

I occasionally get books for review unsolicited, and many of them are not worth noticing. However, Kostas Kampourakis’ Understanding Evolution is a wonderful resource for students of all kinds, including biology students.

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Kampourakis, a philosopher at Geneva, has compiled and discussed sensibly a range of topics concerning evolution. He begins with the conceptual difficulties people have in understanding the evolutionary process, and why. In chapter 1, he discusses how we know about evolution, what questions it answers, and considers two cases that are close to home: domestication and epidemiology, the evolution of disease.

The evolutionary questions are about why living things evolved the way they did, about speciation, the process of evolving new species, and the hypotheses that these require. He talks about explanation (especially “inference to the best explanation“) and the use of scientific method in evolutionary biology. The sections on domestication of animals and on epidemiology are satisfyingly complete.

Chapter 2 covers religious objections to evolution, including, of course, creationism and intelligent design. He discusses the arguments made by ID, especially in the context of atheism and agnosticism. Arguments from design in nature are expounded and given a thorough treatment, including “artifact thinking” and complexity.

The he discusses world views in conflict, especially relating to Richard Dawkins’ views, and then more widely the views of both theist and atheist scientists. Gould’s “nonoverlapping magisteria” and Simon Conway Morris’ inevitability thesis are also reviewed. There is a nice discussion of the differences between knowing and believing and various kinds of methodological and metaphysical naturalisms.

Chapter 3 is titled “Conceptual difficulties to understanding evolution”. Here he discusses psychological essentialism in detail, and the “design stance” that Dennett identified. The problems of conceptual change, which I have published on myself, are then discussed. An example he uses is the shift from geocentric thinking to heliocentric thinking, and it is a good case study. The discussion on essentialism and design thinking, especially of artifacts, appeals to the psychological literature in detail.

Chapter 4 gives a complete and up to date account of how Darwin himself came to his theories. In particular he discusses how Darwin thought varieties became species, and gives a nice timeline of Darwin’s intellectual development. The chapter concludes with a discussion of how scientists and the religious reacted to the Origin.

Chapter 5 is about common ancestry. Usually books of this type focus upon natural selection, as if that were where Darwin’s originality lay. Kampourakis knows that Darwin’s true novelty lay in this idea instead. He explains how genealogical thinking allows us to reconstruct and classify the history of nature, and how thinking in terms of a historical tree of life made all the difference (and was Darwin’s first and main problem to solve). There’s a good discussion of molecular evolutionary biology here.

He gives an account of an often misunderstood notion in biology: homology. This is followed by phylogenetic classification and construction, and a discussion of the question of apparent similarities in biology: convergences (analogy, or homoplasy). Many clear and useful diagrams make the chapter even easier to follow. Then he considers the role of developmental thinking, and how evolution often modifies the timing of development.

Chapter 6 is titled “Evolutionary change”. It discusses “deep time” and dating of taxa and their divergence. Here he notes that while selectionist accounts are important, much evolution is stochastic, that is, chance. He discusses the difference of within-species evolution (microevolution) and between-species evolution (macroevolution) and gives a good summary of scientific ideas about these, especially the “major transitions” literature. The “selection-against” and “selection-for” distinction is explained here. Speciation and extinction are also explained. Then he returns to the question of inference, in a historical science like evolution.

Finally, in his concluding remarks, he discusses what evolution does, and does not explain, especially with respect to ethical and religious questions.

Each chapter has a good reading list, and the material is up to date in both science, and philosophy and history. He takes stances throughout but does so explicitly, allowing the reader to decide what to think for themselves.

This is an excellent, and long-needed book. The education of evolution in schools is now so poor in many countries, that this can act as both a primer and as an invitation to think further, and I would recommend it unreservedly to anyone who wants to know what evolution really is and means. It is not cheap, but neither is it as expensive as many books of its kind. Buy a copy.

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Filed under Biology, Creationism and Intelligent Design, Education, Epistemology, Evolution, Genetics, Philosophy, Religion, Science, Systematics

Survey: What does “Darwinism” mean?

Following on from the last post, I thought I’d do an unscientific self-selected survey on what “Darwinism” means. Please take a few minutes to fill it out.

Click here to take survey

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Filed under Evolution, Philosophy

Closet Darwinism, and definitions

Every so often, somebody makes the case that “Darwinism”, “Darwinist” and “Darwinian”, being the generic noun, the individual term, and the adjective of Darwin’s name and therefore (supposedly) theory, are dead terms that cause nothing but harm (see Scott and Branch 2009). Larry Moran has just made this very argument, refusing to be called a “Darwinist” in the face of the fluffy-lapdog-bite challenge of the Intelligent Designists who want to put every one into the white hat/black hat category. We can ignore them here.

Larry’s argument is roughly this: modern evolutionary theory includes a host of ideas that do not rely upon the ubiquity of natural selection. “Darwinism” and cognates is basically a focus upon natural selection (and hence adaptationist views of biology). Ergo, modern evolutionary theory is not “Darwinian” in the main. I would say both of these premises are correct (of course – Larry is a very clever and erudite man), but that the conclusion doesn’t follow.

Scientific theories are not like, to pick a random example out of my hat,* a religious doctrine or philosophical idea, which remains constant and is defined clearly.** A theory is not a body of ideas; it is a research program as Imre Lakatos called it. It is lines of investigation, based on ideas that are continually refined and revised, often without anyone being aware that is what is happening. And it is a formalisation, usually in mathematics and techniques of analysis, of what start out as verbal formulations.

Consider modern physics. It began with some rough and ready ideas of Galileo on how bodies move, together with some mathematical formulations by Kepler of planetary orbits. When Newton came along and gave a general mathematical account of physics in the Principia, physics did not stop there. In fact, Laplace solved some puzzles (why orbits are stable) as much as 90 years later. And of course, Newton’s work, and the cumulative work of all the physicists in between, like Euler, Lagrange, and many others, occurred before Mach and Einstein came up with our present theories.

It would be hard to “define” Newtonian physics, although there would be some constant simple equations. Likewise, when Darwin proposed “my theory” as he called it, there were many elements to it, some of which did not survive Darwin himself for long (his theory of pangenesis, a theory of inheritance, was effectively dead in the water by 1910, 20 years or so after his death). It is clear that natural selection was one of his major theories, along with sexual selection, but the real novelty of his views was common descent, or as he called it, descent with modification. Natural selection was a refined version of ideas of elimination of the unfit that had a century long history before his own book. Darwin’s novelty was to include natural variation in populations, so that variations that happened to confer some advantage to their bearers would come to predominate the population, ratcheting up the fitness of the group overall.

This idea was not formalised until William Castle in the 1900s combined Mendelian inheritance with selection formally. Later, R. A. Fisher published The Genetical Theory of Natural Selection in 1930. Almost immediately, Sewall Wright introduced the notion of “genetic drift”, whereby populations would “wander” around the “adaptive landscape” due to what he called “sampling error”, where genes could be represented unequally in subsequent populations because of population size and the statistical vagaries of mating. In the 1960s and 1970s, this was further developed as “neutral theory”, whereby most mutations would be “silent” concerning fitness, and through drift could come to be dominant in a population.

All this is often subsumed under the general umbrella of “population genetics”, which was the main evolutionary research program in the 20th century. It culminated in the theoretical work of many, such as Sergey Gavrilets, showing that based on what we know about genetics, genes can evolve just as Darwin saw in nature.

So let’s ask, what counts as “Darwinism”? Sure, a great many philosophically inclined thinkers, like Dawkins, Mayr and others have treated natural selection as the be-all and end-all of “Darwinism”, but in fact the field has always been wider than that. In the 1980s, this got recast as a battle between followers of Dawkins (and indirectly, John Maynard Smith) and Gould (and indirectly, Richard Lewontin), or between “adaptationists” (Gould’s term) and “contingency theorists” (my term).

The point though, is that this is an internecine debate within evolutionary biology, and even more, that both sides claim to be “Darwinians”. I think that from the outside, it appears that evolutionary biology (which certainly derives from Darwin) is like a religion, in that these schisms and schools are all Darwinian. Just as Christianity has a slew of sects, so too does Darwinian biology. The difference is that in the end, biology is determined by empirical evidence, whereas in religion the battles are won by the use of the sword or gun, or more rarely, persuasion based on rhetorical skill.

We might take a term of religion here: “Darwinism” is a big tent. It can include these “non-Darwinian” or “post-Darwinian” ideas because that is exactly how science proceeds. Just as Newtonian physics came to include ideas very unlike what Newton himself had held, so too has Darwinian biology.

Given that Larry is a constant advocate for processes and ideas other than natural selection in evolutionary biology, he might well be seen as not Darwinian in the manner that the adaptationists (whether they think that only natural selection matters, or simply ignore or run roughshod over other processes) are, but historically, he is well within the Darwinian research program, and I suspect he would agree to this. The broad version of “Darwinism”, not the simplistic version of popular science. Larry is Darwinian.

A large part of the problem lies in the way some (for example, Daniel Dennett) have made natural selection the only thing that matters, in any arena let alone biology. Natural selection certainly does matter, but so too do the other implications of a population genetical approach to biology, drift and neutral evolution. Gavrilets has even shown how populations under strong selection can “drift” in high dimensional fitness landscapes of thousands of genes. All this is coming together in ways nobody had thought possible decades before. “Darwinism” is evolving. I take Larry to be a Darwinist, Darwinian in his ideas, and promoting the broad sense of “Darwinism”.

As to the ID folk, basically they do no science, and think very simply. We should ignore what they say as warmed over creationism (creationism also evolves, in this case into ID).

* Not.

** In fact, neither are religious doctrines or philosophical positions, if you ever actually read any history of these fields. Ideas are protean and, dare I say it, evolve.

Bibliography

Castle, William E. 1903. “The laws of Galton and Mendel and some laws governing race improvement by selection.” Proceedings of the American Academy of Arts and Sciences 39:233–242.

Castle, William E. 1910. “The effect of selection upon Mendelian characters manifested in one sex only.” Journal of Experimental Zoology 8 (2):185-192.

Castle, William E. 1911. Heredity: In Relation to Evolution and Animal Breeding. New York, London: D. Appleton and Company

Dennett, Daniel C. 1995. Darwin’s dangerous idea: evolution and the meanings of life. New York: Simon and Schuster.

Fisher, Ronald Aylmer. 1930. The genetical theory of natural selection. Oxford UK: Clarendon Press, (rev. ed. Dover, New York, 1958).

Gavrilets, Sergey. 1997. “Evolution and speciation on holey adaptive landscapes.” Trends in Ecology & Evolution 12 (8):307-312.

Gavrilets, Sergey. 2004. Fitness landscapes and the origin of species, Monographs in population biology; v. 41. Princeton, N.J.; Oxford, England: Princeton University Press.

Lakatos, Imre. 1970. “Falsification and the methodology of scientific research programmes.” In Criticism and the growth of knowledge, edited by Imre Lakatos and Alan Musgrave, 91-196. London: Cambridge University Press.

Scott, Eugenie C., and Glenn Branch. 2009. “Don’t Call it “Darwinism”.” Evolution: Education and Outreach 2 (1):90-94.

Wright, Sewall. 1931. “Evolution in Mendelian populations.” Genetics 16 (2):97-159.

Wright, Sewall. 1932. “The roles of mutation, inbreeding, crossbreeding and selection in evolution.” In Proceedings of the Sixth International Congress of Genetics, edited by Donald F. Jones, 356-366. Brooklyn, NY: Brooklyn Botanic Garden.

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Filed under Creationism and Intelligent Design, Evolution, History, Philosophy, Religion, Science, Theories

When we went wrong

Keating

Paul Keating, prime minister of Australia (1991–1996). Image from The Punch.

There’s a lot of internetz about how current governments are run for the benefit of the plutocracy, and this is both true and worrying for anyone still in favour of free and open democracies. But let us not forget when it started, and how we ignored the warnings. In Australia we have a prime minister who is systematically destroying our environment, our welfare support network, and various sundry other infrastructures that made Australia a good place to live, not to mention the inhumane manner in which his government is treating refugees. But this did not start with Abbott. In fact it did not start with Howard, Abbott’s conservative predecessor and enabler.

This all started when a socially progressive party became neoliberals. The single person most responsible for the parlous state in which Australia now finds itself is a darling of the left: Paul Keating. It began in 1980. Paul Keating was Australia’s treasurer under Bob Hawke, a right leaning unionist who defeated the conservatives is a manner that resembled the last real social progressive of his party, Gough Whitlam in the early 1970s. Hawke was okay, I suppose, but Keating swallowed the Hayekian line whole, and started to introduce the ideas that conservative economists had been floating for a while.

Keating floated the dollar and began the introduction of a foreign idea to the Australian polity: “user pays”. Under his government, the universal health care system was wound back so that private insurance was required by those who could “afford” it (meaning the middle class), while at the same time introducing fees on education to replace the free system that even Hawke’s predecessor, the conservative Malcolm Fraser had preserved from Whitlam.

When Keating was prime minister, his immigration minister, the left faction Gerry Hand introduced mandatory detention for refugees, who had until then been permitted to live and work in the community.

Worse, Keating failed in three policy areas: media laws, public communications, and privatisation. He “saved” the government from having to support public infrastructure by selling it off, either to investors (the rich, in other words) or to companies (corporations, in other words). This then became the watchword for later governments.

When he privatised telecommunications, he allowed on company to control what was then called the Public Telephone Network – the cabling and exchanges of the phone system. This meant that every other competitor had to go cap in hand to a company whose interests were not served by allowing free and fair access to the infrastructure. And they exploited this mercilessly, making competitor customers wait for weeks if not months to connect them. Had Keating kept the infrastructure in one public authority, and made the commercialised companies buy from that authority, we might have a world class communications network by now.

He caved in to the media interests and failed to prevent monopolies. Now nearly all media in Australia is run by Murdoch or his subsidiaries (with ”competitors” that follow his lead), and independent media is almost nonexistent. Consequently the public are systematically misinformed about everything from global warming to political alternatives.

The Hawke-Keating government also destroyed one of the world’s best education systems, collapsing trade and vocational education into universities, and forcing them to raise fees, in the so-called “Dawkins Revolution”. This hurt traditional university education, and also vocational education (I worked for one of the latter institutions, and what were generally industry-relevant courses became academised as the lecturers strove to make their way in academe).

Now Australian education is among the most expensive in the world, rivalling American costs of getting a degree. This has had the effect of making it very hard for young people to get a career.

I could go on. Keating is lionised by the Labor Party as the last really successful Labor PM, but in my view he was nothing better than a right wing plant who was driven by the neo-liberal agenda and ideology, and I blame him for the bulk of bad policy in Australia. He made Howard and Abbott possible.

It is time Australia rejected the legacy of Keating. Both the major parties in Australia are corporatists, and treat the common wealth of Australia as the economy, the whole economy and nothing but the economy. After a reaction to this corporatism, both the major parties had a kick back in a senatorial by election. They now are asking why. If you ask me, it is because of Keating’s legacy, ruining a free country for the benefit of the plutocrats.

It is time to support and vote in the so-called “minor parties” and retake our country back. The “commonwealth” of a nation is the shared infrastructure, both physical and social, that really does “float all boats”, not economic growth as such.

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Speciation – A brief history: The late eighteenth century

After Linnaeus had settled on the older mechanism of hybridisation of genera with other genera or with varieties formed by geographical conditions as the cause of new species, the topic began to pick up speed. Hybridisation remained the usual method as late as the 1830s (e.g., in Lindley) but two developments were crucial in the rise of the “species problem” of the nineteenth century.

One was to do with the degree of freedom in hybrids. Linnaeus had originally held that all species that could exist did, and only later in his work, after around 1751, did he allow for there to be as-yet unfilled possibilities. He had held that all species formed a continuum, like countries with adjacent borders. In his later work, he permitted some regions of the “species landscape” to be unfilled, which hybrids were able to enter. As Peter F. Stevens (1994) has shown, with Antoine Laurent Jussieu (1748–1836) in the French tradition, these regions became more sparsely inhabited. Mechanisms for new species in the uninhabited regions were called for. A “natural system” – one in which the relations were objective (“in nature”) – was called for. But most, such as Adanson and Jaume Saint-Hilaire (1772–1845), still believed that when we had found all species there would be no gaps (Stevens 1994:95ff).

Pierre Maupertuis

Pierre Maupertuis

The other, however, was the introduction of evolutionary, or transmutationist, ideas. Linaneus’ Systema Naturae introduced the notion of species fixity when it was first published in 1735. A mere decade later, the first transmutationist notion of species was published by Pierre Maupertuis, a physicist who also discovered something like the Mendelian ratio. In his Venus Physique (translated as The Earthly Venus) in 1745, Essai de cosmologie, in 1750, Maupertuis wrote:

Could one not say that, in the fortuitous combinations of the productions of nature, as there must be some characterized by a certain relation of fitness which are able to subsist, it is not to be wondered at that this fitness is present in all the species that are currently in existence? Chance, one would say, produced an innumerable multitude of individuals; a small number found themselves constructed in such a manner that the parts of the animal were able to satisfy its needs; in another infinitely greater number, there was neither fitness nor order: all of these latter have perished. Animals lacking a mouth could not live; others lacking reproductive organs could not perpetuate themselves… The species we see today are but the smallest part of what blind destiny has produced… [translation from Glass 1959:58]

In another work he wrote in 1751:

Could we not explain in this manner [of fortuitous changes] how the multiplication of the most dissimilar species could have sprung from just two individuals? They would owe their origin to some fortuitous productions in which the elementary parts [of heredity] deviated from the order maintained in the parents. Each degree of error would have created a new species, and as a result of repeated deviations the infinite diversity of animals that we see today would have come about. [Systèm de la Nature 2:164, quoted in Terrell 2002:338]

Maupertuis’ idea is a revised version of Empedocles’ lucky monsters theory, but it differs in that the parts which recombine are heritable variations of traits caused by blind chance based on what prior parental traits were inherited with “error”. There is no real idea of population or competition, but it is at least in the direction of natural selection.

Later evolutionary (or better, transformist) views included limited varieties such as that of Buffon, through to the universal transformism of Erasmus Darwin or Lamarck. One author was Denis Diderot, whose theory, or better passing comment, is this:

It seems that nature has taken pleasure in varying the same mechanism in a thousand different ways. She never abandons any class of her creations before she has multiplied the individuals of it in as many different forms as possible. When one looks out upon the animal kingdom and notes how, among the quadrupeds, all have functions and parts—especially the internal parts—entirely similar to those of another quadruped, would not any one readily believe (ne croirait-on pas volontiers) that there was never but one original animal, prototype of all animals, of which Nature has merely lengthened or shortened, transformed, multiplied or obliterated, certain organs? Imagine the fingers of the hand united and the substance of the nails so abundant that, spreading out and swelling, it envelops the whole and in place of the human hand you have the foot of a horse. When one sees how the successive metamorphoses of the envelope of the prototype—whatever it may have been—proceed by insensible degrees through one kingdom of Nature after another, and people the confines of the two kingdoms (if it is permissible to speak of confines where there is no real division)—and people, I say, the confines of the two kingdoms with beings of an uncertain and ambiguous character, stripped in large part of the forms, qualities and functions of the one and invested with the forms, qualities and functions of the other—who then would not feel himself impelled to the belief that there has been but a single first being, prototype of all beings? But whether this philosophic conjecture be admitted as true with Doctor Baumann [Maupertuis*], or rejected as false with M. de Buffon, it can not be denied that we must needs embrace it (on ne niera pas qu il faille I’embrasser) as a hypothesis essential to the progress of experimental science, to that of a rational philosophy, to the discovery and to the explanation of the phenomena of organic life. [Denis Diderot, 1753, Pensées sur l’interpretation de la nature, ch. XII, as translated by Lovejoy 1904: 325]

In other words, things evolve over time, but there are no divisions between them, so any classification into species is arbitrary. Hence there can be no “origin of species”, unlike Maupertuis’ views. Diderot here represents the views of the Encyclopedists, of whom he was a leading member as the chief editor of the Encyclopédie. A similar view was espoused earlier by Charles Bonnet (1720–1793), who arrayed species along a continuum from simplest to most complex. Bonnet’s vision was, however, static rather than transformist. Reaction to his scheme was mixed. One rejection was by Peter Simon Pallas, in Elenchus Zoophytorum (1766) , where he argued that we had to represent living things as a branching tree. Again, Pallas was no transformist, but he laid the ground for something like tree thinking, which became the problem Darwin tackled.

Maupertuis’ idea of fitness being what remains after chance has caused variations was not regarded as terribly likely, and on the point of atheism by many. Apart from the hybrid theory, and this, however, there was another idea, not unlike Linnaeus’. That is, speciation by geographical variation. The key figure here is Buffon.

Buffon

Statue Buffon Carlus

Buffon

Georges Louis Leclerc, comte de Buffon (1707–1788) was an influential figure in the eighteenth century. He tended the King’s Garden (Jardin du Roi, later the Garden of Plants, Jardin des Plantes) and wrote a multivolume series entitled Natural History (Histoire Naturelle 1749–1788, in 36 volumes) in which he appeared to post-Darwin scholars to be given an evolutionary theory. In an early volume (1751: “The Ass”) he wrote that species today are “nearly” what they were when created, and that fertility between individuals is what makes a species:

… we can draw a line of separation between two species, that is, between two successions of individuals who reproduce, but cannot mix; and, as we can also unite into one species two successions of individuals who reproduce by mixing.  This is the most fixed and determined point in the history of nature. All other similarities and differences which can be found in the comparison of beings, are neither so real nor so constant.

Later, however, he seemed to present a transformist view: species were not what Linnaeus called species but more like what came to be known as “families”. All canine species formed a group that degenerated from the original dog, all feline species likewise, along with horses, sheep, and cattle. The causes of this degeneration were local climatic and geographical influences upon the seminal fluid and its expression. In the initial essay, he argued that the Ass was not a degenerate horse, because it was infertile when crossed with horses. Later, in “Of the degeneration of animals” (1766), he called the ass a degenerate form of the horse, along with the zebra. As Farber notes (1975: 69):

What Buffon envisioned was the production, in time, of natural genera created by the gradual modification of species. For each genus or family (Buffon used the two words interchangeably) there was an original premier souche [primary stock] that had degenerated into several recognizably different varieties, what we commonly call species. One could show that all the individuals came from a common ancestor by noting their morphological similarity and their alleged ability to interbreed.

This was due to an interior mould (moule intérieur) that caused the embryo to develop into the adult organism; under different conditions, that mould would be expressed differently. Thus a genus or family was the “true” species, and our “species” but varieties of the primary stock. We can classify them all as related because they are the constant forms, despite their outward differences. In modern terms we would call this developmental systems modified by epigenetics (but note: epigenetics means something very different in the period under consideration than it does today. Here it means that the embryo is formed through a developmental process rather than being preformed in the seminal fluid).

Buffon, being a Lockean empiricist as well as a Lockean nominalist, even did a number of cross breeding experiments, with some success, to prove his theory of degeneration. While he got little result from crossing pigs and peccaries, dogs and wolves, dogs and foxes, or hares and rabbits, he did get results from goats and sheep (Roger 1997: 319). Unlike Linnaeus, his vision of hybridisation between “species” in the Linnaean sense was regressive rather than the origin of new species.

Next, I shall discuss the eighteenth century evolutionists Erasmus Darwin and Lamarck.

References

Farber, Paul Lawrence. 1975. “Buffon and Daubenton: Divergent traditions within the Histoire naturelle.” Isis 66 (1):63-74.

Glass, Bentley. 1959. “Maupertuis, pioneer of genetics and evolution.” In Forerunners of Darwin 1745-1859, edited by Bentley Glass, Oswei Temkin and William L. Straus, 51-83. Baltimore: Johns Hopkins.

Lovejoy, Arthur O. 1904. “Some eighteenth century evolutionists. II.” Popular Science Monthly LXV (August):323–340.

Roger, Jacques. 1997. Buffon: A life in natural history. Translated by Sarah Lucille Bonnefoi. Edited by L Pearce Williams, Cornell History of Science Series. Ithaca, NY: Cornell University Press.

Stevens, Peter F. 1994. The development of biological systematics: Antoine-Laurent de Jussieu, nature, and the natural system. New York: Columbia University Press.

Terrall, Mary. 2002. The man who flattened the earth: Maupertuis and the sciences in the enlightenment. Chicago: The University of Chicago Press.

Notes

*. Maupertuis initially published Système de la Nature, based on his PhD dissertation, under the pseudonym of Dr Baumann.

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Filed under Evolution, Natural Classification, Speciation, Speciation Theory, Species and systematics, Species concept

Speciation – a brief history: Linnaeus

440px-LinnaeusWeddingPortrait

Carolus Linnaeus

One of the fundamental aspects of evolution is speciation. This is the process by which more species come into being, and there are many different definitions and mechanisms that have been proposed by biologists in the last couple of centuries. I aim to write an occasional series on what it is supposed to be at various times in the history of biology, as well as the theoretical and, if I get to it, professional aspects.

For there to be speciation, however, there needs to be the possibility of new species. The common view is that this requires a theory of evolution, but in fact, biologists from Linnaeus onwards have posited the generation of new species, even in the absence of anything resembling evolution. For example, during the middle ages, it was commonplace to think new species arose by spontaneous generation (that was the main method that writers about the Ark proposed, along with hybridisation). As I have argued, the notion of “species” itself arose from consideration of the Ark story, as more and more species were reported by travellers and colonisers.

Linnaeus was a creationist, as were nearly all naturalists during the 18th century. He held that varieties within species, and possibly even some species themselves, were but local forms caused by the action of soil, climate and weather. However, he allowed, later in his life, for a kind of speciation by hybridisation. First of all is the famous comment of the species Thalictrum lucidum:

Is the plant sufficiently distinct from T. flavum? It seems to me a daughter of time. [Species plantarum]

What he meant by this is unclear. It is not enough to base a speciation theory on. But he then described four species of Scorpiurus and says

It is beyond all doubt, that all these formerly arose from a single species, and the alteration in the environment is not sufficient for their creation: what commingling has then given rise to the constant plants?

He repeats this about species of GeraniumCalendulaSonchus, and Campanula and the suggestion is they formed by hybridism. As Ramsbottom (1938) from whom I get this, says:

Five varieties of Solanum nigrum appear to be the offspring of hybrids. … he states that the varieties between Fumaria spicata and F. capreolata, judging from their flowers, might be considered as F. oficinalis and queries whether they are hybrids.

Perhaps equally striking is the treatment of varieties in ‘Species Plantarum’ when we bear in mind the definitions repeated two years previously. Far from being merely variations in non-essential characters, they are treated in the same way as species,and as may be seen from some of the quotations already given it is sometimes queried whether what is described as a species is only a variety or vice versa.

Rowbottom doesn’t think Linnaeus has changed his mind from the earlier Philosophica botanica. Instead he thinks this is something Linnaeus had always allowed. Linnaeus’ student Daniel Rudberg in 1744 had discussed the possibility of hybrids forming. And in 1746, another student, Johannes Gustavus Wahlbom, had discussed hybridisation in tulips. He explained it as degeneration: related species were a degradation of the original species, a view Rowbottom ascribes to Aristotle’s student Theophrastus. A modern botanist would assign this to plesiomorphic (underived) developmental systems, which is not so far removed. In  1751, his student Johannes J. Haartman described a hundred species thought to be hybrids on taxonomic grounds. Several other students made similar comments, quoted by Ramsbottom.

Although Linnaeus famously supposed that a genus, Peloria, was the result of hybridism between a flower of Linaria and some unknown plant, which he published in 1744 after Gmelin had responded to a letter from Linnaeus with news that he had found some hybrids too (Gardiner 2001) [1], he finally made his views explicit in a tract, Disquisition on the sex of plants, in 1760, in which he wrote:

There can be no doubt that these are all new species produced by hybrid generation. And hence we learn, that a mule offspring is the exact image of its mother in its medullary substance, internal nature, or fructification, but resembles its father in leaves. This is a foundation upon which naturalists may build much. For it seems probable that many plants, which now appear different species of the same genus, may in the beginning have been but one plant, having arisen merely from hybrid generation. … these Geraniums, I say, would almost induce a botanist to believe, that the species of one genus in vegetables are only so many different plants as there have been different associations with the flowers of one species, and consequently a genus is nothing else than a number of plants sprung from the same mother by different fathers. But whether all these species be the offspring of time; whether, in the beginning of all things, the Creator limited the number of future species, I dare not presume to determine. I am, however, convinced, this mode of multiplying plants does not interfere with the system or general scheme of nature

So Linnaeus held that from an initial plant with a variety of possible forms and parts, hybrids could generate some, but not an open-ended number, of new species. In a tract published two years after this, his student Johannes Mart. Gråberg wrote:

We imagine that the Creator at the actual time of creation made only one single species for each natural order of plants, this species being different in habit and fructification from all the rest. That he made these mutually fertile, whence out of their progeny, fructification having been somewhat changed, Genera of natural classes have arisen as many in number as the different parents, and since this is not carried further, we regard this also as having been done by His Omnipotent hand directly in the beginning; thus all Genera were primeval and consisted of a single Species. That as many Genera having arisen as there were individuals in the beginning, these plants in course of time become fertilized by others of different sort and thus arose Species until so many were produced as now exist. … That also some Genera multiplied into very numerous Species…. That these Species were sometimes fertilized out of congeners, that is other Species of the same Genus, whence have arisen Varieties.

Todays genera are the original creations of God. Ramsbottom says

The same theory of progress from simple to compound, from few to many (e simplice progressus ad composita; e paucis ad plura!) was repeated in the sixth edition of ‘Genera Plantarum’, 1764.

Linnaeus fixism was widely adopted, although it was in part based upon an artificial system, by Linnaeus’ own admission. He wanted a natural system – one that explained the underlying causal relationships between plants – but never was able to produce it. As late as 1830, John Lindley was calling Linnaeus’ system “natural”, remarking

Nature herself, who creates species only (Lindley 1830, xvi).

The genera were God’s creation here, too. Linnaeus’ ideas that species were generated was a commonplace. His ideas of the diversification of species by hybridism, however, while it was not used as the foundation for much research, became part of the botanist’s mental toolkit. This is not surprising, though, as naturalists had used hybridism as an explanation of new and deviant species since Aristotle had written about it for animals in the Historia Animalium, and Theophrastus in his Enquiry into plants. Later, hybridism was the foundation of Mendel’s researches, to which we shall return.

References

Gardiner, Brian G. 2001. “Linneaus’ species concept and his views on evolution.” The Linnean 17 (1):24–36.

Lindley, John. 1830. An introduction to the natural system of botany: or, A systematic view of the organisation, natural affinities, and geographical distribution, of the whole vegetable kingdom: together with the uses of the most important species in medicine, the arts, and rural or domestic economy. London: Longman, Rees, Orme, Brown, and Green.

Ramsbottom, John. 1938. “Linnaeus and the species concept.” Proceedings of the Linnean Society of London 150 (192-220)

Notes

1. It was not. It is an epigenetic mutation, neither concept of which was available to Linnaeus.

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Filed under Biology, Evolution, History, Natural Classification, Speciation, Speciation Theory, Species and systematics, Systematics

The origins of “speciation”

As I do some research on the history of speciation theories, I came across this, which is perhaps the original coining of the term:

Evolution is a process of organic change and development, universal and continuous, and due to causes resident in species. Speciation, to give the other process a name, is the origination or multiplication of species by subdivision, usually, if not always, as a result of environmental incidents. Speciation is thus an occasional phenomenon which does not cause evolution, and is not caused by evolution. One procession of organisms may be divided into two, but it does not appear that the new groups will travel in any different manner than before, nor that they will go any faster or any farther than if they had not been separated. The subdivision enables the two parts to follow different roads and to arrive at different destinations, but it does not assist the evolutionary locomotion nor give us any clue as to how it is accomplished. The evolutionary interest of isolation is that each case affords additional evidence of continuous, progressive change as the normal evolutionary condition of all groups of interbreeding organisms. The isolation of a new group is an interesting biological event, a crisis, as it were, in speciation, but it gives us no special opportunities of studying the causes of evolution. [Cook 1906:506]

By 1939, a Society for the Study of Speciation had been set up, although it lasted only a few years (Cain 2000). The 35 years following Cook’s paper were a frenzy of studies, theories and arguments.

Cain, Joe. 2000. “Towards a ‘Greater Degree of Integration’: The Society for the Study of Speciation, 1939-41.” The British Journal for the History of Science 33 (1):85-108.

Cook, O. F. 1906. “Factors of Species-Formation.” Science 23 (587):506-507.

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Filed under Ecology and Biodiversity, Evolution, History, Speciation, Speciation Theory, Species and systematics