I’m reading Sean Carroll’s new book, The Big Picture (it’s very good; I’ll provide a review when I’m done), and once again I got balled up about the difference between Einstein’s General Theory of Relativity and his Special Theory of Relativity. I can never get them straight, no matter how many times I look them up—just like I used to confuse the historical difference between Sunni and Shia Islam (I can now remember that one).
When I got confused this time, I thought, “Maybe a physicist would consider this difference something that every educated person should know.” And then I thought, “What would I want every educated person to know about my own area of study—evolution?” Well, there’s a lot I’d like people to know, like what the evidence is for evolution (that’s why I wrote WEIT), but if I had to summarize what I’d want people to know in just one paragraph, I suppose I’d say something like this. (Nit-pickers: I wrote this in a few minutes and haven’t gone over it obsessively.)
There are five parts to the “Darwinian theory of evolution”. First, evolution happens: that is, populations are genetically transformed over time. That means that the genetic constitution of a population changes from one generation to the next, not that individuals themselves change genetically. Second, that change of populations is gradual: substantial evolutionary transformation, like the evolution of bony fish into amphibians, takes thousands to millions of years. Third, evolution involves more than just transformation of populations, but splitting of populations—what we call “speciation.” One lineage can divide into two or more lineages that can’t exchange genes with each other; and those new lineages can themselves split. This produced the “tree of life” that, starting with one ancestral species about 4 billion years ago, produced the millions of species living today as well as the millions that have gone extinct without issue. Fourth, if you look at the splitting process in reverse, starting with any two twigs (species) on the evolutionary tree, you can, if you go back in time, find a common ancestor those species, just as if you take any two twigs on a tree and move down, you’ll find a common branch or node that they share. All living things are thus related, and the more recently their common ancestor lived, the more closely related they are (that’s the definition of “closely related”). Finally, the “designoid” features of organisms—the features that make them look so well adapted to their environments and lifestyles—are the product of natural selection: the combination of a random process, mutation, that generates genetic variation without regard to whether it’s “useful” or not, and a deterministic process, selection, that winnows the variation by retaining those mutations that are better able to make copies of themselves and eliminating the worse copiers. There are other important processes of evolutionary change, like random genetic drift, but only selection can produce the design-like features that so excite our wonder. And we have strong evidence for every one of these assertions, so that the “theory” of evolution is “true” not only in the sense that it’s the best explanation we have for how life changed on Earth, but also because we have copious evidence from many areas of biology supporting all five contentions.
That’s pretty much the way Darwin laid out the theory, though of course he knew nothing about genetics or “random” mutations. And, by and large, these propositions still stand up today. There are some exceptions of course: the origins of mitochondria in cells didn’t involve just gradual change of a single species, but the integration of one species with another, somewhat blurring the “treeness” of life. We also know a lot more about the process now than we did when Darwin limned it in 1859. But the paragraph above is what I’d expect anyone who considers themselves educated to know about evolution.
Not all readers are academics, of course, but most of you have fields in which you work and, presumably, would like others to know what’s important about that field. If you feel so inclined, write a sentence or paragraph about your “area”, and what people should know about it to be considered “educated.” If there’s too much to say, just pick out one thing to highlight—perhaps a fact or misconception.