The Phlogiston Theory is not equivalent to the Aquatic Ape Hypothesis.

In recent days the Internet science community has got its collective nickers in a mighty twist. The disciples of the Aquatic Ape Hypothesis (AAH) have dared to hold an international congress in London and the, oh so irresponsible, press has wasted precious print and cyber space reporting on this frivolity. For those not in the know the Aquatic Ape Hypothesis claims that certain aspects of human evolution can only be explained by assuming that a group of anthropoids, the future humans, lived for a substantial period in water. My evolutionary theory expert friends assure me that this hypothesis is a festering heap of non-scientific nonsense, as was forcibly expressed by Henry Gee in this Guardian blog post. So far so good but a couple of science writers thought it would be a good idea to draw parallels between the AAH and one or other historical scientific theory with disastrous results.

The first of these was Ben Richmond writing on The Mother Board in his post How the Aquatic Ape Theory Keeps Floating On. Mr Richmond chose to equate the AAH with the Ptolemaic geocentric theory. He wrote:

But the aquatic apes theory is more like Ptolemaic models of the cosmos that Copernicus overthrew. These models of the solar system had to be ever more complex to keep the Earth in the middle and also account for the incongruous movement of the planets. In the end Copernicus’s moving the Sun to the center of the solar system simplified the model

This paragraph is of course a complete myth that has absolutely nothing to do with what really happened in the sixteenth century. As this is a standard myth that gets repeated time and time again I shall briefly sketch, not for the first time, the true facts of the story.

The Ptolemaic models developed in the Middle Ages, first by Islamic astronomers and then, most recently before Copernicus, by Peuerbach actually became simpler not more complex. The Peuerbachian geocentric model in use as Copernicus published his De revolutionibus was actually simpler than Copernicus’ heliocentric model. The contemporary astronomers hoped that Copernicus’ model would at least deliver more accurate data on the positions of the heavenly bodies, the, at the time, principle function of mathematical astronomy but the Copernican system based on the same data as the Ptolemaic systems was just as inaccurate as its predecessors. Heliocentricity only “overthrew” geocentricity as Kepler developed his actually simpler and much more accurate elliptical astronomy in the first quarter of the seventeenth century.

Ed Yong, notable science writer, chose a similar tactic and compared, in a tweet, the AAH not with geocentricity but with the phlogiston theory of eighteenth century chemistry.

Ed Yong tweeted:

After the recent shadow biosphere piece & this wk’s aquatic apes one, I look forward to the Obsever’s exposés on phlogiston & cold fusion

Rebecca Stewart praised his audacity in another tweet:

Phlogiston is sooo underrated!

Karen James crowned him a master tweeter for this piece of brilliance

That last tweet shows why @edyong209 is considered a master tweeter. I suppose we shouldn’t be surprised; tweeting is writing, after all.

This comparison is just as wrong as Richmond’s and casts a poor light on Ed Yong for having made the comparison. Yong’s tweet and those of his supporters imply, at least unintentionally, that AAH and the phlogiston theory are equivalent in their scientific status a complete fallacy. The AAH is a highly dubious hypothesis that does not according to Henry Gee, even agree with the know facts of evolution theory whereas the phlogiston theory was an important scientific research programme, which played an important role in the evolution of chemistry in the eighteenth century.

It is very easy from our standpoint in the twenty-first century to pour scorn on the theory of phlogiston, which viewed whiggishly, that is in comparison to our current knowledge of chemistry, can in some of its aspect appear more than somewhat ridiculous. However viewed within the context of the situation in which it was born the phlogiston theory made a great deal of sense.

Phlogiston arose at the end of the seventeenth century when the dominant theory of matter was still the four-element theory of the ancient Greeks. This had been supplemented by the tria prima concept of the Paracelcians. On top of the four Greek elements of earth, water, fire and air Paracelsus had added the principles of mercury, sulphur and salt. It is important to realise that these are principles involved in the composition of substances rather than substances themselves. In an analogy based on the combustion of a piece of wood Paracelsus compared the smoke to mercury, the flame to sulphur and the ash to salt. This analogy is important, as combustion alongside distillation was one of the two principle methods of chemical investigation available to alchemists in the Early Modern Period.

Whilst rejecting Paracelcian alchemy the German physician Johann Joachim Becher (1635 – 1682) borrowed the tria prima replacing the mercury, sulphur and salt with three forms of the element earth:

terra fluida or mercurious earth, which contributed fluidity, subtility, volatility and metallicity to substances.

terra pinguis or fatty earth, which produced oily, sulphureous and combustible properties.

terra  lapidea or vitreous earth, which was the principle of fusibilty.

Becher published this theory in his Physica Subterranea in 1667. For Becher his terra pinguis played an essential role in combustion.

Another German physician Georg Ernst Stahl (1659 – 1734) took up Becher’s theory, in 1718, renaming terra pinguis, phlogiston, from the Greek meaning inflammable, using this principle to explain both combustion and corrosion (rusting). Hypothesising that all inflammable materials contain phlogiston, which is consumed or used up during combustion. The important point is that the phlogiston theory as developed by Stahl readily explained the known facts of combustion.[1]

Working within the phlogiston research programme, in particular English chemists such as Joseph Black, Daniel Rutherford, Henry Cavendish, James Watt and Joseph Priestley isolated and discovered a whole range of elemental and compound gasses and furthered the evolution of chemistry over the next sixty or seventy years. In fact it was using the discoveries of the phlogistonists that Lavoisier and others were able to produce the synthesis that became known as modern chemistry. This dependence on the phlogistonists was so great that the great German nineteenth century chemist Justus Freiherr von Liebig stated in his third Familiar Letter on Chemistry: “He discovered no new body, no new property, no natural phenomenon previously unknown; but all the facts established by him were the necessary consequences of the labours of those who preceded him.”[2]

Supplanted by the Lavoisier’s synthesis phlogiston became an obsolete theory one that viewed from the new standpoint of the facts that it had discovered was no longer able to explain the available evidence a fate it was soon to share with Lavoisier’s own contribution to the evolution of chemistry.

Above I said that viewed whiggishly, that is in comparison to our current knowledge of chemistry, can in some of its aspect appear more than somewhat ridiculous. Interestingly the, now, Cambridge historian of chemistry Hasok Chang has written a brilliant paper titled We Have Never Been Whiggish (About Phlogiston)[3], in which he takes a new whiggish look at the phlogiston theory and its successor. I recommend this paper to anybody wishing to equate the phlogiston theory to the AAH.

Unfortunately it is common practice for people largely ignorant of the history of science to equate modern pieces of idiocy with obsolete theories from the evolution of science that having served their purpose and having been superseded by other theories are then considered as suitable subjects for ridicule. This is wrong, with a probability approaching certainty all of the scientific theories that we use today will someday themselves be superseded by better or more explanatory theories and become in their turn obsolete. This will not make them ridiculous but they will become part of a long chain of theories that have facilitated the evolution of science. Theories that no matter how strange they might appear to us from our privileged position of hindsight should be treated with the respect that they deserve for their important contribution to the advancement of knowledge.









[1] This very brief account of the origins of the phlogiston theory is largely taken from, William H. Brock, The Fontana History of Chemistry, Fontana Press, London, 1992, pp. 78-86.

[2] I owe this Liebig quote to regular Renaissance Mathematicus reader and commentator Arjen Dijksman (@materion) to whom I’m very grateful.

[3] Hasok Chang, We Have Never Been Whiggish (About Phlogiston), Centaurus, Vol. 51, 2009, pp. 239-264.


Filed under History of science, Myths of Science

16 responses to “The Phlogiston Theory is not equivalent to the Aquatic Ape Hypothesis.

  1. Phlogiston seems to get a lot of bad press.

    I first heard of it in high school, probably the chem class. It left a positive impression with me. It was a theory that led Priestley to do some critical expiriments that turned out to be the beginnings of modern chemistry. What more can you ask of a theory, than that it inspire a whole new direction for science? Okay, that new science was also the undoing of phlogiston. But science has to start somewhere, and phlogiston worked as a starting point.

    By contrast, AAH leads nowhere.

    • You sum up my post perfectly in half a dozen sentences 😉

    • marc verhaegen

      For an update of the aquarboreal theory (on Mio-Pliocene hominoids incl. australopiths) & the littoral theory (on early-Pleistocene archaic Homo)”, pleae google “two incredible logical mistakes 2020 verhaegen” + refs.

  2. Phlogiston theory was also Kuhn’s standard example of so-called “Kuhn loss”, where a new theory loses some explanatory power possessed by its predecessor. Phlogiston theory explained “why metals had so many more properties in common than did their ores” (Structure, p.99), which Lavoisier’s theory failed to do.

    As for Ptolemaic astronomy, I’m starting to wonder if Peuerbach actually did simplify Ptolemy. I state this diffidently, as I have a lot more reading to do here. I have not yet been able to come up with an “epicycle count” over 32 for the Syntaxis (that’s epicyles plus deferents plus equants …) Peuerbach adds spheres to make it a mechanical rather than a purely geometrical description — at least that’s how it looks to me at first perusal. (Apparently Ptolemy already proposed this in another work.) Wikipedia says that the oft-quoted figure of 80 epicycles referred to a descendent of the Eudoxian homocentric spheres, a very different beast.

    As for the rant, I hope it felt good to write it — it felt good to read it! You don’t believe this sort of lazy journalistic shorthand (phlogiston=crazy-think, etc.) can be stamped out, do you?

  3. Hmm, I see you omitted the previous paragraph from Ben Richmond’s piece, which was even worse:

    Pseudoscientists love to fashion themselves as modern Copernicuses whose ground-breaking, paradigm-shifting discoveries are being oppressed by the “priests” of the age, just as the Church covered up the Renaissance astronomer’s theory of the Sun in the center of the solar system with the Earth revolving around it. [emphasis added]

  4. Tim O'Neill

    Wikipedia says this about Purbach’s model:
    “Purbach is also noted for his great attempt to reconcile the opposing theories of the universe, the so-called homocentric spheres of Eudoxus of Cnidus and Aristotle, with Ptolemy’s epicyclic trains. This work, Theoricæ novæ planetarum, had an enormous success and remained the basis of academic instruction in astronomy until years after Nicolaus Copernicus had swept away all these hypotheses.”

    So “swept away” by Copernicus?

  5. As I understand it, the key issue was whether the heavenly spheres really existed, or whether you just had a geometrical scheme to “save the phenomena”. It’s easy to see how the Eudoxean scheme accomodates actual spheres, not so obvious with the Ptolemaic system as presented in the Almagest.

    Peuerbach’s Theoricae Novae Planetarum has been translated by E.J.Aiton (Osiris, 2nd Series, Vol. 3 (1987), pp. 4-43), but I’ve only skimmed it; I need to reread it more carefully. Here’s how Aiton describes it in his intro:

    Peurbach’s Theoricae novae planetarum introduces the reader to the Ptolemaic geometrical models as embodied in the physical realizations described by Ptolemy in his Planetary Hypotheses.

    It’s clear from the figure on the opening page that the Theoricae wasn’t strictly homocentric, but employed eccentric spheres as well.

    Ptolemy “swept away” by Copernicus? I don’t think so. An adequate discussion would also have to include geo-helio-centric (Tychonic) models; I believe many astronomers preferred a geo-helio-centric version of Kepler to the real thing, once the Rudolphine tables had shown that ellipses were here to stay.

  6. Ian Paul Wragg

    ” I believe many astronomers preferred a geo-helio-centric version of Kepler to the real thing,”

    Michael, I take it you mean “Tycho Brahe” rather than Kepler?

  7. I meant the Tychonic system modified to use Kepler’s first two laws. In other words, kinematically it is equivalent to Kepler’s system, but physically it still has a motionless earth.

  8. Thanks for this post; an excellent reminder of the differences between building on a theory (which then modifies/disproves the theory it started from), and work that seemingly has no foundation. I spend a long time trying to explain this to my students in relation to medieval understandings of the world and the cosmos (particularly maps of the world). I think I’ll be making your post required reading!

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  11. Of course, the term “aquatic ape” is wrong. Human ancestors were anatomically & physiologically not adapted to running over open plains, as some anthropologists still claim. Instead, Pleistocene Homo populations simply followed the coasts & rivers in Africa & Eurasia (and even reached islands such as Flores >18 km overseas), google, eg, “econiche Homo”.

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  13. It’s now obvious (see the recent papers on the subject in JHE 2014) that early-Pleistocene Homo simply dispersed intercontinentally along coasts & later rivers, rather than running over dry open plains (scarce in water, sodium, iodine, poly-unsaturated fatty acids, easy to catch foods etc.) as a few conservative PAs still believe:

    “The aquatic ape evolves: Common misconceptions and unproven assumptions about the so-called Aquatic Ape Hypothesis”
    Marc Verhaegen 2013 Human Evolution 28:237-266, 2013
    While some paleo-anthropologists remain skeptical, data from diverse biological and anthropological disciplines leave little doubt that human ancestors were at some point in our past semi-aquatic: wading, swimming and/or diving in shallow waters in search of waterside or aquatic foods. However, the exact scenario – how, where and when these semi-aquatic adaptations happened, how profound they were, and how they fit into the hominid fossil record – is still disputed, even among anthropologists who assume some semi-aquatic adaptations.
    Here, I argue that the most intense phase(s) of semi-aquatic adaptation in human ancestry occurred when populations belonging to the genus Homo adapted to slow and shallow littoral diving for sessile foods such as shellfish during part(s) of the Pleistocene epoch (Ice Ages), presumably along African or South-Asian coasts.
    … Conclusions:
    Many scientific as well as popular publications on the so-called aquatic ape theory or aquatic ape hypothesis give incorrect impressions of how, when and where our semi-aquatic ancestors could have evolved. This paper provides arguments from diverse biological subdisciplines for the following three hypotheses, which to conservative anthropologists might seem unexpected at first sight, but are based on what is known from other animals: the comparative evidence.
    (1) The aquarboreal theory of Mio-Pliocene hominoids suggests that our Miocene and Pliocene more apelike ancestors and relatives, including the australopiths, led an aquarboreal life, living in wet forests such as flooded, mangrove or swamp forests and later in more open wetlands, and fed on hard-shelled and other plant and animal foods at the water surface and the waterside as well as in the trees.
    (2) The littoral theory of Pleistocene Homo (AAH sensu stricto) suggests that early-Pleistocene archaic Homo populations dispersed along the coasts, where they reduced climbing adaptations, but frequently dived and used stone and other tools for feeding on shallow-water and water-side foods including shellfish.
    (3) The wading hypothesis of early Homo sapiens suggests that, later in the Pleistocene, Homo populations gradually ventured inland along the rivers, reduced diving skills, and frequently waded with very long and stretched legs and fully upright body to spot prey in very shallow water and used complex tools to collect different sorts of aquatic and waterside foods.

  14. marc verhaegen

    For an update of the littoral theory, google
    “coastal dispersal Pleistocene Homo 2018 Verhaegen”

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