ResearchBlogging.orgPerhaps we are all subject to falling into the trap of what I call the Hydraulic Theory of Everything. If you eat more you will be bigger, if you eat less you will be smaller. Emotional states are the continuously varying outcome of different levels of a set of hormones, forming “happy” or “stressy” or “angry” cocktails. Your brain is a vessel into which life pours various elixirs. Too much of one thing, and there will not be enough room for something else. Even political arguments are hydraulic. The ‘balanced’ middle view between two arguments is like the mixture of contrasting primary colors on a pallet.

a repost

But some, even many, things in life do not work this way. The body stores or uses fat, and obtains energy from various sources, and controls energy through metabolic level and activity levels, such that there is not a clean, simple one to one correspondence between pieces of pie and inches of waistline. The mid point between two opposed political argument very rarely actually exists, and even more rarely would ever be accepted by anybody. And so on.

A very non-hydraulic system that is often seen as one is genetic inheritance. The traits that the average person knows about seem to blend more often than not. A person seems to be a mixture of that person’s parents. Even when there are digitally distinct traits, there are numerous such traits, some following mother, some father, some the mail carrier, such that the gestalt of the offspring still seems like a blend of parents. Hydraulically, like a martini or a Minnesota hot dish.

And that is how Darwin thought inheritance worked, and this misconception kept that great thinker and great experimentalist from figure out the relatively simple conclusions adduced by Gregor Mendel.

Heredity and variation were two concepts that played a central role in Darwin’s development of the theory of evolution by natural selection. The enormous effort he devoted to their analysis is reflected not only in the entire two-volume The Variation of Animals and Plants under Domestication, but also in countless experiments and observations narrated elsewhere. Yet despite a lifetime’s efforts, he never came close to understanding the logic of inheritance, while his views on the nature and causation of variation oscillated back and forth between a concept of random, quasi-physical events outside environmental control, which indeed looks decidedly modern, and a concept, evidently owing much to his predecessors, of environmentally driven adaptive change transmitted to the germ cells.

This is the opening paragraph of a paper, just out, by Jonathan C. Howard, asking “Why didn’t Darwin discover Mendel’s laws? The paper, in the Journal Biology, is an excellent and detailed discussion of this question. And it really is not simple. It has been proposed in the past that Mendel was more prepared than Darwin to figure out inheritance, given the particulars of his training and background. But Howard, while agreeing that this may be true, points out that Darwin had seen and to some degree recognized what were thought of a “units of inheritance” of certain traits, traits of interest to breeders and the like, but rejected their importance in the larger evolutionary picture.

(In other words, Darwin did not think that Micro evolution was too important!)

Howard explored Darwin’s “Pangenesis” hypothesis, and explores the idea that Pangenesis predisposed Darwin to understand variation as continuous, and not discontinuous, as one would have to do to really get genes.

The important and interesting thing about Howard’s thesis is to unravel the standing argument about why Darwin did not advance a viable genetic theory.

Darwin is occasionally criticized as an imprecise, nonnumeric naturalist, a man of ideas, perhaps brilliant and original in that mode, but not a scientist like those of today. … Mendel’s rational, experimental analysis of the inheritance of unit characters is without question a work of great genius. …. However, if Darwin failed to discover Mendel’s laws, it was not so much because of what he lacked in genius or numeracy or the experimental cast of mind, but rather because of the forceful tendency of what he already possessed. His focus on continuous variation as the source of evolutionary change was not wrong, and coupled with the power he could see in the integration of infinitesimals over time he built his case on the solid foundation of Lyell’s uniformitarian thinking. Much of variation and inheritance was simply opaque in those terms, but continuous variation, not unit characters, was, for Darwin, the way forward. Thus Darwin boxed himself in, unable to see the laws of inheritance in continuous variation, unable to see the real importance of discontinuous variation where the laws of inheritance could be discerned.

… Which is really, or at least also, a problem with Lyell as well as Darwin, this confusion and conflation uniformitarianism and uniformness. Even Steve Gould got that wrong. But we’ll talk about that some other time.

Jonathan C Howard (2009). Why didn’t Darwin discover Mendel’s laws? Journal of Biology, 8 (2) DOI: 10.1186/jbiol123


  1. #1 Jim Thomerson
    November 24, 2009

    I suspect this is one of those multi-cause effects. Darwin was in fact not good at math, although he excelled in plane geometry. Mendel, on the other hand, had a strong background in physics and math, and was prepared to think like a physicist about natural phenomena; that complex results could result from simple interactions of simple factors. Remember also that Mendel’s work was not appreciated until around 1900, and was not really integrated into evolutionary biology until the ’20’s and ’30’s. It was stongly resisted by the biometricians, Carl Pearson for example, who thought of variation much as Darwin did.

  2. #2 frog
    November 24, 2009

    Hrmm, how could Darwin think that discrete inheritance was unimportant in evolution? How could he, given that one can show mathematically that continuous distribution of traits makes speciation, etc, next to impossible?

    Because he didn’t do the math. That simple — he thought that by staring at data and “thinking” about it, one could (and should) do science — that the data “spoke for themselves”. If I recall correctly, Darwin blamed it on his training in the geology of the period, and thought it was a terrible mistake on his part and on part of the field.

    I think the question goes the other way — it’s amazing that he was so correct despite the crappiness of his early scientific ideology. His personal brilliance must have been quite impressive for him to overcome the intellectual handicap produced by his training.

  3. #3 David
    November 24, 2009

    Darwin understood Lyell’s continuous model of geologic change as being built of small increments from discontinuous process. For example, in Beagle he observes an earthquake and deduces that the Andes are built of the accumulation of small, but isolated, events. It’s a simple analogy from there to seeing continuous change in biology as the accumulation of discrete genetic changes. So I don’t buy the idea that Darwin was too tied to a world view of continuous change.

    While we’ll never know, I think the answer lies more in the mathematical ability and quantitative outlook of Mendel. His approach to inheritance was numeric from the outset, whereas Darwin’s was always descriptive.

  4. #4 Ford
    November 24, 2009

    Somewhere I saw a letter he wrote noting that sex is a discrete trait (male x female => male or female, not some mix) and speculating about the broader importance of discrete inheritance. So close!

  5. #5 toto
    November 25, 2009

    From what I’ve heard, many people thought Mendelian genetics were incompatible with the continuous variation observed in several traits (such as size).

    It wasn’t until Fisher that people realised there was no contradiction. When you apply mendelian laws to many independent units of heredity, you get the same results as with “blending” inheritance.

    If not being as good as Fisher (who pretty much invented statistics) makes you a bad mathematician, how many good mathematicians are there on the planet?

  6. #6 C. Sullivan
    November 25, 2009

    A better question might be why Mendel’s laws were not independently discovered by Francis Galton, Darwin’s cousin and scientific associate. Galton, like Fisher, was a pioneer in the field of statistics, and he was deeply interested in heredity – he even ran experiments on the inheritance of size in sweet peas!

    No one could reasonably claim that Galton was a poor mathematician. His cast of mind was both quantitative and experimental, but he never made the leap to viewing heredity as particulate rather than continuous. In my opinion, this suggests that mathematical ability was not the key to the critical idea of “non-hydraulic” heredity. Galton, like Darwin, really did box himself in by focussing on continuous variation.

  7. #7 bioephemera
    November 25, 2009

    Maybe I’m missing something, but I think this is the same Howard paper that came out last spring, which I blogged about here?

  8. #8 Paul S.
    November 25, 2009

    As someone who likes to speculate about alternate historical outcomes, I wonder how the biological sciences would have developed differently if Darwin had learned of Mendel’s work and appreciated its significance in connection with his own. Would a synthesis of evolution and genetics decades earlier have pushed a much faster scientific development, or would it not have made much difference because scientists at the time lacked the experimental tools and knowledge to really take advantage of it?

  9. #9 Greg Laden
    November 25, 2009

    Bioephemera, yes, this paper came out last srping. I took the opportunity of it being the 24th to repost a couple of Darwin related posts.

  10. #10 bioephemera
    November 25, 2009

    Aha! I knew I was missing something. Happy Thanksgiving, Greg! 🙂

  11. #11 Greg Laden
    November 25, 2009

    I should make my “repost” thingie larger. I used to have a big time machine graphic but it was a lot of trouble.

  12. #12 Jim Thomerson
    November 25, 2009

    If you get a chance, do visit the Mendel Museum in the Abbey of St. Thomas in Brno. I toured it in 1991 while it was in development. Learned a lot that I did not know. For one thing, Mendel was a accomplished plant breeder. The usual photo shows him holding a flower from one of his fuschias. There was an apiary at the abbey, and Mendel planned to study the genetics of bees, but did not do so. This is rather fortunate, I think, as he likely would have been totally confused.

  13. #13 Greg Laden
    November 25, 2009

    There was an apiary at the abbey

    Indeed. Few people realize that Mendel was a great collector of apes.

  14. #14 Philip Bruce Heywood
    December 1, 2009

    A bee in abbey?

    Darwin would have done better had he 1) Spent a long time here in Australia, studying, amongst other things, ORNITHORHYNCUS, the Platypus. A composite if ever there was a composite? I don’t see how contemplation of a few species along the lines of good old ORNY could lead to any conclusion other than that species are some sort of statistical outcome of environmentally triggered (not environmentally created) outcomes acting on a finite set of genetic possibilities. I take it that’s where Mendel’s maths leads. 2) Darwin should have spent even more time contemplating the thoughts of the world leading systematic palaeontologist of the day, Richard Owen. Owen advized him outright that his theory didn’t explain the fossils and put forward the idea that species had an ability to transform according to a definite purpose, this transformation being something outside the power of environmental pressure alone to achieve.
    Owen didn’t have the benefit of electronic computation, DNA, and quantum information theory. Mendel’s maths, of course, is one with Owen’s notion of species transformation. Nothing in this universe happens without maths!– looking at ORNITHORHYNCUS, there we have a mathematical expression. Finite number of discreet available characteristics acted on by environment to trigger (not originally create) a workable, if bizarre, combination – a species.
    Darwin saw the importance of environment but gave it something approaching creative powers. He was blind to the mathematical basis of everything, as emphasized centuries before by Galileo. Hence, Darwin inadvertently misled Science into a pre-Renaissance mindset.

  15. #15 Greg Laden
    December 1, 2009

    Why is it that when I see a comment that is 92 paragraphs long and starts with “Darwin would have done better had he…” I tend to want to go on to some other project…