Quetelet and the origin of statistical and population thinking

Adolphe Quetelet is a much overlooked figure in the history of scientific methodology: he marked that populations had distributed properties that were largely constant, even though individuals varied in ways that seemed indeterminate. He noted that hat sizes and belt sizes were constantly distributed in different samples. Will Thomas at Ether Wave Propaganda has a good piece on him.

It is often stated that Darwin started what Mayr and others have called “population thinking”, but as Michael Ruse has shown, Darwin was influenced by Quetelet’s statistical thinking as early as 1838, and that, allied with Darwin’s knowledge of variation in natural populations, led him to what I like to call a “snowflake” view of populations – they are all alike in some ways, but they vary. This provides the variation on which natural selection can act, and Darwin spent as much effort as he could documenting this.

So far so good: Darwin’s population thinking is the major shift in thought etc., etc. Except, I don’t think Darwin was all that consistent in his population thinking. I think he saw varieties as classes of traits, that were differently adapted. I don’t think he ever really thought of populations as statistical ensembles in the strict sense, and that he developed his idea of it over time. I also think that class-thinking is at the base of such essentialistic accounts of biology as gene centrism. We are inclined to think in terms of equivalence classes, and so we need some kind of thing that “carries” the variation.

Genes seem to be the right sort of thing, so we focus on their general properties: especially replication. But Darwin neither needed these entities with special properties nro was he eventually drawn to conclude they existed on the basis of his theoretical structure. Instead, he went the other direction, moving towards what Edward Conklin called “blending inheritance” in 1922. Ronald Fisher wrote that blending inheritance need not be antithetical to darwinian evolution, but that the rates of blending need to be outpaced by the rates of novelty, and more recently several philosophers, Jim Griesemer and Peter Godfrey Smith being two of the more significant ones have instead utilised the notion of a “reproducer” instead of replicators, and this need not be something that exists at a particular level.

Godfrey Smith in fact holds that the primitive notion of evolution is the population. A reproducer is something that can be counted in a population. I am not entirely convinced of that – to be a population one has to have some idea of what one is counting (is there a population of bee colonies or of bees?). The solution, I think, is to use phylogenetic inferences. You know the sorts of things to count for this species because you know the sorts of things that its cousins have. This implies to me that the primitive, that is to say, the basal, conception here is the species; but maybe there’s a bit of slip here – we sometimes know what the species is, and sometimes what the population is, and each illuminates the other. And sometimes the unit of a population, the reproducer, is hard to identify, and we have to use phylogenetic context to figure it out. Biology is messy, after all.

Population thinking took a long time to sort through – I reckon we are still trying to get it clear. We are essentialists by nature, and we need to be educated to think in a different way. The temptation to revert to essentialism is always present, but if science learns about the world, we should make our ideas conform to the world, not the other way around. And that means taking population thinking seriously. More seriously than Darwin, more seriously than Mayr even.