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