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.

25 thoughts on “Speciation – a brief history: Linnaeus

  1. I wonder if I could get some clarification on “hybridisation,” as viewed by Gråberg, Linnaeus, Rudberg, Wahlbom and Haartman.

    From the Gråberg quote, it sounds like he thought each genus was monospecific to start with. Some individual plants were later “fertilized by others of a different sort” (from a different genus?) to produce new species (belonging to what genus?).

    Only after that could there be “hybridisation” as we usually know it today, involving reproduction between two (so-called) “species” of a given genus. (?)

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    1. Yes, I wondered that myself. I think it must be that genera hybridised to form new species. The genus they appear in depends on which was the parent that provided the pollen. Linnaeus and many others thought that there was a dominance in male “seed” so a hybrid will typically belong to the male’s genus.

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  2. “The difficult question, which is also a new one, is whether a female plant can be fertilized by a male of another kind, the female hemp by the male hops; the castor bean from which one has removed the staminate flowers, through pollination with the pollen of Turkish wheat (maize); and whether, and in what degree altered a seedling will arise therefrom.”

    Camerarius, 1696

    https://openlibrary.org/books/OL6729744M/Plant_hybridization_before_Mendel

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      1. Don’t I know – it is just interesting to see all the evidence they had from their detailed study and how the underlying theory so influences the interpretation.

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        1. Yes, it’s a good thing today’s scientists don’t behave like that any more.

          [Sarcasm alert.]

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          1. Of course it is true for today’s scientists – why wouldn’t it be? But Richard, it is what creationists do also – you can’t try to feel superior. This is what keeps science interesting – explaining new data and revising old theories. When creationists can describe their god’s or gods’ mechanisms – I will be very interested to hear from them.

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            1. “Can you also, Lucullus, affirm that there is any power united with wisdom and prudence which has made, or, to use your own expression, manufactured man? What sort of a manufacture is that? Where is it exercised? when? why? how?”
              Cicero, Academica II (Lucullus) XXVII, 87.

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            2. Certainly, you’re right on that score, Michael. All of us interpret evidence in light of our presuppositional philosophical framework. The evidence does not actually “speak for itself.”

              Regarding mechanisms of origins, philosophical naturalists/materialists/physicalists still have a lot of work to do. At the moment, their various proposed mechanisms for the origins of the universe, life, and biodiversity tend to be negative, destructive, and not likely to produce complexity out of disorder or simplicity. Mechanisms like the Big Bang singularity (an explosive miracle); Life from Nonlife (in opposition to known tendencies of chemicals); Mutation (degradation of genetic information); and Natural Selection (early deaths of a lot of organisms).

              Just as Darwin wrote in the second last sentence of his Origin of Species: “Thus, from the war of nature, from famine and death, the most exalted object which we are capable of conceiving, namely, the production of the higher animals, directly follows.”

              God’s creative mechanisms, to the extent we are allowed to know them currently, are revealed in Genesis chapters 1 and 2.

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              1. It makes me laugh when creationists complain that scientists don’t have all the answers. Who knew there were still unanswered questions in science? Another guy was whinging that phylogenetic trees change over time – as if this were a problem for common ancestry. This is how science is different than religion – you can’t just sit on a mountain top waiting for a revelation – you have to do some actual work and hard work at that. And modern creationists aren’t even waiting for a revelation, they think it happened to some unknown individual 1000s of year ago – believed without question.

                If Genesis were a description of what happened, then why have Christians bothered with science at all? Linnaeus was wasting his time doing anything but writing down species names – everything that needed to be known about origins was already known. But we know the actual story is different, Genesis is wrong – dead wrong – the chronology, the description of organismal group membership, the mechanisms of species creation, etc. Why do we know this – because people like Linnaeus actually did the hard work and when they were done – the actual answer was different than the one they started with.

                If your theory no longer explains the data, then you revise or change theories. This is what happened in the 17th through the 19th c. – Genesis as a explanation was tossed on the scrap heap of scientific theories. And before you start whinging about evolution – yes it could be tossed too if it didn’t work any longer. Even if evolution were wrong, Genesis would still be wrong. The answer would be something we haven’t thought of yet, not something that was obviously wrong 200 years ago.

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              2. “It makes me laugh when creationists complain that scientists don’t have all the answers.”

                The problem I pointed out was not a lack of answers. The problem is that the mechanisms that have been proposed by philosophical naturalists are scientifically unworkable.

                “If Genesis were a description of what happened, then why have Christians bothered with science at all?”

                The assumption in your question is that Christians have indeed bothered with science. This assumption is not only true, it is heavily understated. Christians were prominent in the Scientific Revolution and actually originated many scientific fields.

                Now as to “why” that should be so, here are three answers (additional ones are possible, of course):

                (1) For the glory of God;
                (2) To benefit the human race;
                (3) Because Scripture inspired them to do so.

                Science: Child of the Biblical Worldview http://www.creationbc.org/index.php?option=com_content&view=article&id=87&Itemid=62

                How a Literal Understanding of Genesis Promoted the Rise of Modern Science! http://www.creationbc.org/index.php?option=com_content&view=article&id=117&Itemid=62

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              3. I do recognize that it’s your website, John.

                However, I was rather sharply provoked.

                And as I pointed out in my previous post, a historical argument can be made that creation-based thinking strongly promoted science. It’s only “antiscience” to folks persuaded by the current reigning philosophical view. (We certainly don’t see ourselves as “antiscience.” I’ll restrain myself from including a link about that.)

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              4. Well there is a (studied?) ambiguity in the claim that “creation thinking” had anything to do with the rise of science. In fact, the underlying principles of creation were simply the background against which science evolved, as everyone was a creationist, so it is not necessarily the case that it promoted science, especially since science did not develop for the preceding 1500 years of “creation thinking”.

                And in fact as soon as science got going, it systematically deflated and debunked creationist thought. While it is true that the initial thinking about the diversity of life in the 16th century was based around Noah’s Ark, that had ceased to be the case within a century, as colonists sent back specimens to the scientific community and geographical maps were refined. Moreover, geology undercut the rather short chronology implied by the Bible, no later than the 1790s.

                I do not even think that Christianity has much to do with science, pace Peter Dear. Instead, I think that science ran more or less parallel to religious beliefs, which were employed only so long as no scientific explanation had been produced. In every historical case of which I am aware, as soon as science produced something workable, it trumped theological sources (including scriptural ones).

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              5. “I do not even think that Christianity has much to do with science, pace Peter Dear.”

                I had not previously heard of Peter Dear, but your mention of this Cornell science historian would appear to indicate that an informed scholarly argument can be made that Christianity did have something to do with the rise of science.

                Could you possibly provide a link to something relevant by Peter Dear that I can read without having to pay money? :)

                While trying to find out about Peter Dear, I came across this interesting piece by Harrison on the early Royal Society: http://www.faraday.st-edmunds.cam.ac.uk/resources/FAR312%20Harrison.pdf

                “And in fact as soon as science got going, it systematically deflated and debunked creationist thought.”

                Those opposed to the Bible, such as Hutton, Lyell, and Darwin, may have thought they were debunking it. But what they were doing — to go back to Michael’s earlier comment — is just interpreting evidence in “light” of their anti-biblical philosophical presuppositional framework.

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              6. Richard, modern post-Darwin creationists are simply not doing science because they don’t understand how science works. You don’t start with the answer and then use only the data that confirms your theory and discard everything else and never, ever change not matter what the data are. Science doesn’t rely on authority. This is very different than the pre-Darwin creationists who as you say were Christians and who evaluated the evidence and concluded creation was wrong. You cannot have it both ways – claiming that Christians “created” science and then when those same individuals conclude that Genesis is not historically or scientifically correct to claim that they weren’t Christians. Those scientists did not set out to undermine Christianity – most would have claimed publicly that they were trying to understand their god by studying its creation. The shift into science was a shift from relying on ancient authority whether the Greeks or the Bible and relying on observation and experimentation. Modern creationists have almost nothing in common with those Christians who started practicing science – early scientists realized that everything was open to question – something modern creationists are unwilling to do. So please stop projecting your non-scientific world view onto scientists – it just doesn’t fit.

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              7. Michael: “Richard, modern post-Darwin creationists are simply not doing science”

                If science had one clear universally-agreed-upon definition, you could possibly make a case for your statement. But it doesn’t. Only if use a narrow, tendentious definition of science deliberately formulated to exclude creationists can you strongly argue that creationists are not doing any kind of science.

                When creationists propose scientific arguments against ruling scientific paradigms (e.g., Big Bang, biological evolution), how can you say they aren’t doing science?

                And if creationists’ scientific arguments are valid — which I think at least some of them are — then they are arguably doing very good science.

                But either way, they are doing science, on that front. And that’s only one of several angles from which your statement can be challenged.

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              8. About the role of Christianity in the development of modern science: if you’re doing history instead of writing polemics, “Christianity” isn’t a very useful term because virtually all the players were at least nominally Christian in the 17th and 18th Centuries. Peter Harrison’s thesis, if I understand him, is not that “Christianity” inspired the scientific revolution—a pretty feeble generality—but that a very particular strain of Christianity played a very particular part for very particular reasons. Harrison relates the emergence of the Baconian practice of science to Puritanism. One should read the Book of Nature as the Reformers read the Book of God, i.e. literally. Hence the impatience with highfalutin theories and the insistence on the careful accumulation of facts. Thing is, though, if you read the Old Testament literally and then attempt to correlate its chronology with archaeological remains and its account of creation with rock formations, you’ve got a problem. I’m an enough of an Hegelian to appreciate the idea that Biblical literalism generated its own negation, but I don’t know how far you can go with this theme. When Smith made the first great geological map, he was tracing coal seams, not looking for evidence of the flood; and anybody who spends enough time tromping around road cuts and examining strata will eventually recognize the obvious falsity of the Biblical story whatever their motives.

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  3. I went away and read Sir Thomas Browne on this. He believed that transmutation or transplantation as he termed it, was most commonly observable in plants. But he arrived at that perspective by rejecting the notion of ‘male’ or ‘female’ in relation to plants. (he thought it was an ancient perspective based on folk belief). lacking such sexual distinctions they were imperfect and more prone to hybridization.

    Subject has a fascinating history. I get the impression its a subject highly prone to cultural fantasy and high degrees of anxiety through a large stretch of time (in relation to a fear of otherness I suspect).

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    1. A history of hybridisation in natural history from the medieval to the pre-modern period (say around 1700) is badly needed.

      I am mostly covering the post-modern period, from Linnaeus onwards, as there is a pull of the recent in natural history/biology which motivates it. But histories of hybridisation (such as Jan Sapp’s) are very modern indeed.

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  4. What catches my eye is the subject in relation to Jewish and Arabic species concepts on a number of counts.

    But I would also like to see the degree to which the sensation of taste informed classification in regard to Jewish species concepts. Although that may prove to be something of a Barnacle Goose.

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    1. “A barnacle goose” is now my preferred term for some subject that leads into a morass of references and connections. No, wait, my preferred term is a “species concept”.

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  5. When i think of the barnacle goose the words that spring to mind are pleasing and to wonder.

    At times I think you can detect the same emotional qualities in legions of past thinkers exploring the world around them through such imaginative constructions.

    The goose in its embryonic form was thought to lie in rock pools by day “drinking in the sun”

    A wonderful thing in a world ripe for dreaming.

    “Pleasant to me the sunshine/ for the way it glitters on these margins so”

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