Perhaps 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.
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
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I'm a lurker, but I'm willing to de-lurk to discuss history of science! I didn't read the article though, so my thoughts might have been covered there and I'm just repeating others.
Mendel found that his laws of inheritance worked for seven traits in garden peas. His benefactor suggested that he try the experiment in another pea species, but that species was more complex genetically and had many more chromosomes than the garden pea. IIRC, Darwin did hear of Mendel's laws, but because they didn't hold true in all species, he regarded them merely as an interesting curiosity.
What I find odd is that it wasn't until the 19th century for genes to be discovered. It's not like it required a certain technology to discover the concept. In principle, an ancient Roman could've discovered it. I find it odd that no one ever figured it out in the more distant past
It is my understanding that a copy of Mendels' paper was found among Darwins' papers after his death but, because it was written in German and Darwin had only a poor understanding of German, he failed to realize the its importance. If the paper had been written in Latin or French, things might have been different.
I made inquiries about the possible mutual knowledge between Darwin and Mendel (from the creator of a site called MendelWeb back in the 1990s ) and was told that the copy of Origin in Mendel's library is massively written on by Mendel (I suggested that someone should publish the annotations). I was, further, told that there was a copy of Mendel's work in Darwin's library--but the pages were uncut. So Darwin may not even have needed his poor understanding of German.
Iain
All very interesting comments. I would like to point out that although the details of genetics were not worked out by Darwin and Mendel had questions and limitations, etc., the basic concept of inheritance, of hidden traits, of dominant traits, of some of the complexities, etc. really did exist in many cultures at that time including in Eruope. It isn't as though there was either no knowledge whatsoever or perfect knowledge.
What I got from this paper is that the imperfect knowledge is in a sense what was getting in the way.
Also eventually it will be understood that Mendel's basic dom/recessive binary genetics does not actually explain much of the important stuff anyway.
I do think there were differences of nature and background between Darwin and Mendel which are important. Darwin did not do well with algebra. Mendel had extensive knowledge of physics and mathematics. He thought in terms of the physics ideas of discrete particles and complex results from a few simple causes.
Having spent 30+ years teaching Mendelian genetics at the introductory level, I think Mendel's ideas are difficult to grasp. Dominance really confuses the picture and requires an additional set of assumptions about dominant and recessive. I soon shifted to using some of the later examples where complete dominance is not present: yellow, cream, and white guinea pigs; red, pink and white four o'clock flowers, etc. Then coming back to Mendel and introducing dominance.
Should you get the chance, a visit to the Mendel Museum in the Abbey of St. Thomas in Brno is quite worthwhile.
This discussion of Mendel has many implications for the development of a quantitative science of memes--cultural units. I have proposed a new scientic field of mememetrics--an empirical, quantitative, statistical approach to the study of memes, specifically a domain of ideologies or isms.
Quantitative scores for ideologies yield clear profiles for political party preferences, religious adherence, and domestic partnership as contrasted to marriage. By the way, Rush Limbaugh's speech at the conservative meeting is a prototype of a conservative ideology.
I've always wondered about that myself. Thanks for answering it.