You knew it’d have to come to talking about natural selection one day.
My purpose here is to talk about teaching this subject. Maybe biology isn’t a special case, but in my experience, whatever anyone brings into the classroom, in their head, regarding Charles Darwin’s ideas about natural selection, must be sandblasted outta there before anything useful or accurate can happen. Anyone. Bio majors or nonmajors, freshmen or seniors, undergrads or grads, and frankly, plenty of faculty who are supposed to be teaching it too.
Truth: I had way less trouble explaining this phenomenon, and seeing good results on tests and papers, to evangelical Christian students in south Georgia than to self-designated “evolutionists” wearing Dawkins t-shirts in Chicago.
So, teaching: a look behind the prep. I figure you can look up the phenomenon in technical terms at a thousand places on the internet. The trouble is, start in on that in a classroom, and everyone will be hearing something else. These are some points I hit early to clear that out.
Selection. Which is not the same as evolution. Evolution is any ol’ substantive change to biological diversity. Selection is one way that it happens; it gets pride of place for being the first major proposed mechanism.
Minor point: Darwin’s original term natural selection is fine as a historical thing, in which “natural” meant material, physical, and (for lack of a better word) mundane. However, speaking in teaching terms, it’s sort of disastrous. The term “natural” carries immense implications of purpose and rightness for the student listener and they think that’s what you mean. So I simply say “selection” to help focus on a physics-based, historical set of events.
Also, so-called artificial selection differs from any other sort by not a bit of anything, so that distinction doesn’t need to be emphasized as strongly as it was at the time. If you really want to fight about that, I’ll say “artificial selection is a case of natural selection in which people happen to be involved, so the term is merely of clinical interest unless you want to say people are artificial or unnatural.” It’d be most accurate to call this selection used as technology.
So, when the what-this-is discussion does start, another phrase I don’t use is “how it works,” which gets inferred a purposeful device or engineered process. Teaching mantra: it’s not what you mean to say, it’s what they hear you say. If you don’t get them to explain it back to you, in their own words rather than parroting yours, then you don’t know what you’ve been teaching. My aim is for them to see that selection doesn’t have to happen, but given its three famous conditions, it will. (what, not four? shock! just three – “more are born than survive” is a common condition, but it’s actually not a physical requirement) And also to see that we’re talking about changes inside a species via generational time, not the fate of a species.
Consider carefully, too, these two phenomena, which are subsets or versions of how it happens:
When a specific sector of genetic content is directly truncated, “editing” I guess you might call it. Tempting as it is to use it as the go-to example (it’s usually dramatic), it’s only really selection if the reproductive demographics are altered. That’s why the peppered moth might be a bad example – just because more or less of a particular color are getting eaten (and are hence less present to observation), doesn’t have to mean the production of the next generation is skewed the other way; the predation has to hit the potentially breeding adults before they do it. I prefer using the soapberry bugs native to Florida, whose little probosci vary from short to long as they feed upon the also-native balloon vine … but toward the north part of the state, where they’re feeding on the introduced flat-plodded golden rain tree, their little probosci lengths are clustered in the low end of the former range. This shift is permanent – the longer probosci, or rather their genetic component, are simply gone from the local population.
You see how in both of those (granting that the moths may be an example after all), the “changed state” is merely a subset of the wider variation prior to the events. Compare that to more subtle events which change the way something is done. Body size is a good example – the change or shift in genetic content is itsy-bitsy compared to the astronomically more numerous genetic effects and conditions which stay the same, but the former changes the pace and/or some non-trivial step of the latter. Selection does that kind of thing too – probably a lot more.
Now lookit, lookit what’s not in there.
- “survival of the species,” technically, a longer species longevity, whether as some overall thing or in view of impending extinction
- decreased longevity, i.e., hastened extinction for some other species
- a fortuitious mutation that “comes along” which also happens to be “what’s needed”
- ruthlessness toward anyone
- an identifiable fit feature or fitness in general before the current generation are all dead
- origin of a new species – whether selection’s involved in these very common events is a hot topic, but nothing about selection as such makes speciation a predicted outcome
- improvement in the circumstances or life-experience of individuals in the species
- a solution to a designated “problem” for the species (this concept overlaps with a couple of others on this list but is worth stating as a thing of its own)
- change in population size, whether increased for this species or decreased for another
[Here I might go on a blogger’s toot about Friedmanite
economics horse shit and how selection isn’t a “market” (whatever these gnomes claim that is in the real world), but that would divert from what I’m trying to get across about teaching this stuff. It’s only relevant because some bright-eyed little expert may start chirping about it. A later topic, I say to him or her, and so, here, a later topic too.]
Here’s a useful example, using this bit of snuff porn from Planet Earth (don’t get me wrong, great show, but fair warning and all that):
- The wolf isn’t selecting anything about the calf, or the caribou in general, in terms of what you’re looking at. The commentator is right in saying the outcome depends on happenstance details of that exact moment. This isn’t a “weaker” or “lesser” calf.
- Has selection resulted in the current speeds of the two animals, or more accurately, in the average speed for each one’s species and exact demographic? Sure, very likely, to the point of outright saying yes. But so what? Caribou still die mainly by eaten by wolves, it just happens at a higher speed than it used to. They didn’t “solve their wolf problem” via selection’s wonder.
Seeing how much you might be up against yet? Why you might not want to start with Hardy-Weinberg equilibria and such? And as if all that were not enough …
Adaptation. I don’t use this term, for two reasons: what the students come in with, much as the above, and what they all too often find. That latter is why, as my thinking’s turned out, I’ve come to question it as a valid scientific term at all. Or at best, as an unnecessary and baggage-laden synonym for selection.
The first problem is that it’s totally ambiguous regarding process vs. product. The problem with using it to refer to a product (endpoint, whatever you call it), is that “adaptedness” gets elevated to something special rather than merely change due to selection. Can you be “not there yet,” “poorly-adapted,” “well-adapted,” “unadapted,” “finished” … is there some identifiable state in which we know we’re looking at a real-and-true adaptation rather than … some crap version? That’s rhetorical; the answer is no. The only thing we see is what the critter has, and unfortunately, calling it “adapted” all too often is debased merely to mean that we think that’s pretty cool.
The second problem is the association with purpose, engineering, and machine-tooling. This crops up when we talk about adapting “to its environment” (for what? resulting in what?) This is also where “fit” and “niche” do their damage, or rather, confirm the damage unless introduced as deeply technical and in fact advanced terms, later. Even worse when the redemptive or triumphalist issue of survivorship comes into it, whether for individuals or species. News flash: all individuals die, and all species go extinct. If adaptation is supposed to be preventing these, then it’s a pretty limp dick of a natural phenomenon.
The source page for this image says, “Mimicry of leaves by insects is an adaptation for evading predators.” No, it’s not. “For” is simply not an operating physical phenomenon in the actual world; it is not a statement of cause. I’ve seen profs say this and much like it, and then spend the rest of the term trying to untangle themselves with “but what it meant was.” Stop the madness. Say it like it happens instead. … And when you do, you’re simply doing regular ol’ selection again, in which the prevailing most relevant impact on reproductive success was predators, and in which (more importantly) there were and are a myriad of tweakable developmental details already there in the collective genome of the species.
In other words, if adaptation is a process, and if it’s rigorously phrased without reference to a “final” “product,” then again, we’re just talkin’ about plain old selection and don’t need another term rattling around.
Oh yeah, and then there’s the confusion about whether adapting is something a creature does with multiple states, like fur color changes by season, or a single optimized thing it does – kind of a Holy Trinity problem there actually. Or the larger version of the same question, whether being adapted means “adaptable,” i.e. living across multiple ecological conditions, or “exquisitely suited” to one – pretty different things for one term.
Hammering on the drum again … it doesn’t matter if any of these interpretations of or confusions about the term are entirely made-up by students based on some who-knows-what out there, or if it was an older implication or association with the term that scientists are trained to abandon – just because the students are wrong doesn’t let you off the hook. They’re going to think that’s what you are saying unless you scotch it from the start, test’em on it, listen to what they say when they have to word it themselves, and keep playing whack-a-mole.
To conclude, and at last, consider the images I’ve included of an elephant’s trunk. The circular logic falls apart instantly: apparently only the proboscid mammals “needed” a trunk, and glory be, they “got” a trunk … they got it ’cause they needed it, and they must have needed it because they got it … was there supposed to be a cause involved in here, again?
In this circle lies the most sticky and invisible trap of all: the argument from beauty. I grant you fully: this organ does things, it is striking to behold (to our eyes), and the creature who owns it is easy to empathize with. That some process arrived at this organ as such, to make it, in order (wonderfully) to have it, is so lovely that even thinking it is like reading a fine haiku. If the world were such a place, such that it writes haiku for us … that’d be a world most fine to live in. And if you want to believe that, you go right on ahead, but as a teacher, the minute you invoke, imply, or permit to be inferred that this belief is a physical process on this here earth, you have just become a mystic. A smug one who claims “only” to be describing nature in action. Whole lotta smug mystics out there calling themselves atheists.
The biggest, most embedded, most crufty thing is the urge for some earthly process to be a story, for something we empathize with to encounter adversity, to do and to struggle, and to rise or fall. For the way of the world to be theater, whether didactic or gorgeous or anything else.
That’s why I didn’t go into the whole “survival of the fittest” abomination in this post. It ain’t nothing but theater, and it ain’t Darwin either. Look forward to that later.
Next: Hermes and Aphrodite