Adapt and die

This one gets into the biology of extinction, especially in comparison to its presence in broad, pervasive popular culture and ideology. Rarely has so much been wrongly inferred from so little, and I find I have to teach it from the bottom up, no matter who’s in the classroom. As usual, there are two levels of confusion: the larger, social one, and the within-biology one. I’ll be dealing mainly with the latter, which underwent a serious review right at the time that I was deciding to get into evolutionary biology as a career.  If you don’t mind a little support reading, check out Adapt this and New Synthesis zaps.

That’s an easy point to muddle. We belong to a high-risk extinction group by being a big, anatomically-derived social mammal. Among our group, though, H. sapiens was and is less-risk because of its broad geographic distribution and generalist diet and climate tolerance. So if any of us were to make it through the Pleistocene, it’d be that one.

I hope you can see that it’s not a process, or any component in a cycle, or any sort of other systemic phenomenon. It’s an outcome that occurs due to at least one of a huge, uncountable number of completely understandable, physical ways to wind up there. A species’ exact selective history plays into the probabilities, but selection as such isn’t acting as a preventative measure. At the philosophical or narrative level, I stress that a species doesn’t go extinct when it “does something wrong,” or when “it’s just its time to go,” or for anything.

That goes double if you over-interpret the process of selection as being for anything.

One important mental illusion to dispel is the notion of replacement by one’s direct descendant, or the notion that species X “makes way for” or is “beaten out” by the species which has evolved specifically from it.

But even if extinction isn’t about direct descent-and-replacement, isn’t it about the stronger species surviving? Nope. I know why people held onto that, though – natural history does offer a couple of cruel traps to lead you that way if you’re inclined.

That needs a bit of clarifying – the interaction between northern and southern mammals of the Americas should get a post of its own and I don’t mean to say there was no competition in the community-ecology sense of the term. However, it was an event of mammalian history, not a defining or archetypal one.

Community ecology is endlessly fascinating and endlessly aggravating; its practitioners seemed bound and determined to arrive at non-contingent models for exactly what would happen, always. The “superior species prevail” model was well-established a century ago when Georgy Gause ran his test-tube bacterial trials and posited the concept of competitive exclusion, and the concept stuck hard. Even when field research suggested that overlapping species with similar resource needs tend to spread out into mosaic distributions rather than battle it out to the finish, and also that actual competition was not the likely mechanism leading to those distributions, the textbooks wouldn’t let it go. (here – see how tentative and hesitant the challenge is)

Now for the two types of extinctions:

In retrospect, it’s cool to remember that Raup’s ideas about mass extinctions – amplified by Gould’s columns in Natural History, collected in his books -were arriving at the same time as the big revision of understanding dinosaurs physiologically, specifically, endothermic based on varying definitions of the term, and not great big addled lumps of failed stupidity. Don’t forget that the Chicxulub Crater was discovered in the late 1970s, lending immense credence to reincorporating catastrophism into our understanding of geologic, evolutionary time, and helping to dispel the blame-the-victim narrative for the events of the K-T boundary.

At the time, it seemed as if mass extinction were the more challenging concept, and its explanations are painstaking to overcome the historical assumption of gradualism-and-nothing-but. However, it didn’t really have much trouble penetrating either scientific or popular level. Background extinction, on the other hand, tends to get less attention. On the one hand it’s simply the Rule of Explosions in action; y’know, if this thing explodes and this other thing doesn’t, we tend to want to check out the first. On the other, I suspect the concept of background extinction is (i) challenging story-oriented interpretations of evolution that people are still reluctant to release, and (ii) inherently disturbing.

Here’s a bio bumper sticker for you: every living thing is a living fossil. The relevant scientist to credit here is the incomparable Leigh Van Valen.

One of the biggest problems is matching the neutral and non-directive observations about background extinction to the question of ecological policy. Pound for pound, conservation efforts have managed the biggest social impact through sentimentality: showcasing a really cool creature (i.e. easy for humans to empathize with) and warning that it’s about to go extinct. As outreach, one can only say “it works,” but as genuine policy-making relative to scientific knowledge, it’s unstable ground. It pitches extinction as a terrible wrong, something that would never happen to this creature without human impact … so saying “species go extinct all the time” undermines the message and gets taken as an endorsement of not trying to save this one or (more importantly) this one in the context of its habitat. One can certainly acknowledge the reality of background extinction and support specific conservation efforts especially in circumstances of human impact, but in the world of soundbites, which has always been the world of legislative effort, using whatever technology, that lacks the fundamentalist ker-clunk of naturalism-to-principle-to-action that makes things happen.

Here’s a last detail to nail down the lid on this whole “selection saves the species” romance.

The final concept to disintegrate in the light of these concepts is yet another cherished narrative – the notion that evolution, and specifically natural selection, is something to do with carrying on the species. That the persistence of a species for one generation more is somehow an imperative – whether physical drive, or moral responsibility, “Nature,” however you want to cast it. That species extinction is the “evil” being avoided by ecological and selective phenomena as a version of the medical model, that death is the “evil” being avoided by the virtues of good hygiene or medical tech.

It’s an interesting world when you look at it without that exact story playing in your head.

Next: A wonderful day in the neighborhood

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7 thoughts on “Adapt and die

  1. I definitely remember the buzz surrounding the re-evaluation of dinosaurs when I was growing up during the 80s-90s. There was a particularly good episode of The Infinite Voyage (an otherwise totally forgotten documentary series) covering the subject that to my delight has been preserved for posterity on youtube:

    (There’s a nice little soundbyte from Gould here, BTW)

    More recently, an extra nuance that I took away from Climbing Mount Improbable was the possibility of ‘local minima’ in the fitness landscape with respect to some particular aspect of morphology- e.g, the distribution of blood vessels behind or in front of the retina in mammalian vs. cephalopod eyes. It’s hard to see how our blind spots confer a special contextual advantage, such that if you could somehow take the human genome and substitute a cuttlefish’s retina-building instructions, one couldn’t say ‘yup, that’s a better body plan’.

    I’m not saying, e.g, placental vs. marsupial birthing represents this kind of morphological grudge-match, but is it all likely, over the span of earth’s history, that either species or taxa might get overrun by distant relatives who took a different fork in the road? (This is purely amateur speculation on my part, with no particular training in either genetics or morphology, so please correct me as needed.)

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    • Hi! It took me a bit to sift through my thoughts for a reply. To step back a little, it seems to me that the term “adaptive landscape” makes sense only in a microevolutionary context: the distribution of genetic variation and environment for a single species in a relatively short period of time. I have concluded, sometimes reluctantly, that its frequent use as a species-comparative device (or interpretation) is simply not justified by our understanding of the broad array of things that cause evolution.

      In other words, I simply don’t see any validity to the idea that species’ differences from one another are primarily a matter of local selection – in other words, given a standard dispersal and allopatric speciation situation, that if we could switch out exactly who went into each of those environments, we’d see the same results. It’s related to the notion that the geographic landscape sets the adaptive landscape, and that the creatures’ diversity at the species level reliably reflects that precise relationship.

      These ideas were called into question on very good grounds by the mid-1990s, and it boggles me a little that, in recent conversations with colleagues and with interested blog readers, it seems still to be the prevailing concept.

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    • Here’s another point: that selection, which by definition occurs within a species, and interspecific competition are profoundly different things. The latter might be an important context for the latter, but on a case by case basis subject to research scrutiny, not as a fixed or overriding principle.

      That’s the core idea for my next point: that yes, by anyone’s analysis, the North American mammals’ entry to South America led to the extinction of the native mammals. But what does this mean in evolutionary terms? It is not selection. It’s a circumstance of extinction. Consult the definition of selection and you’ll see what I mean.

      The best analysis I’ve seen – I’ll have to hunt for the ref later, as I encountered it as a talk at a meeting – suggests that placental/marsupial had nothing to do with it. Instead, the key was the difference between North and South America(s) in raw geographical terms: the former is broad east-west and the latter is elongated north-south. That means a lot of the northern species could have very wide distributions due to consistent light/dark cycles, across many microenvironments, and the southern ones had a much higher rate of endemism (small, origin-specific distributions) instead. Therefore in a species competition context, (i) the northern ones included wider environmental tolerances and (ii) the southern ones were easy to “nail” because each was confined to a limited range.

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      • I appreciate the info Ron, but given I’m barely familiar with what ‘allopatric’ means I’m not certain I can comment that usefully…

        Given your recent post on urban rat populations, maybe it’d be useful to touch on, say, the modern-day introduction of rabbits to Australia, or other cases where a species that was manifestly very poorly adapted to the landscape nonetheless managed to cause plenty of extinctions?

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        • “Allopatric” = fully separated; it’s the easiest context for discussing speciation, so that’s why I specified.

          I’m not sure what you mean by “poorly adapted to the landscape” for the invasive rabbits. Are you stating it this way because they’re not native to the area? If so, then this is a good example of the problems inherent in the term adaptation, especially its confusing and unresolved status as both process and product. I began discussing that with Adapt this, developed in further posts too.

          Briefly, there is nothing meaningful in the term “adapted” aside from being synonymous with “selected.” The latter is the better term because it only refers to a process, with no reference to an endpoint or to any special qualities of the outcome. Several such things always lurk in the term “adapted,” implying (for instance) that a species has a distinctly low chance of extinction, or is contributing to ecosystem stability, or is abundant, or is resistant to short-term shocks (like a new predator), or, and I know this is strange but people think it all the time, is happy or fulfilled in some way.

          I feel as if this conversation is a little bit fogged; it’s hard to see whether you’re asking something vs. having something in mind you’re trying to get across to me. I’m critiquing what appears to be a strong foundation (under your replies in this post) based on the term “adaptive landscape” in reference to multiple species. Let me know whether you want to me to go into explain/clarify mode, or whether you want to do that yourself instead.

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        • You’re good to offer Ron, but rather than eat up your time I think I’ll have to do some independent reading, and maybe get back once I have some more background.

          To clarify briefly about Australian rabbits: I was suggesting it’s hard to argue that rabbits are ‘a good fit’ for the (physical) landscape because their transient population explosion(s) tended to trigger heavy soil erosion- i.e, undermine conditions needed for their own survival, along with native species.

          I realise that’s an imprecise formulation, but this is basically my belabored way of saying ‘I agree’, as regards displacement == superiority, with an example stark/simple enough to wrap my head around, and wondering if that would make a good post topic.

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        • I see what you meant. It is unfortunately ‘way in “to be gently corrected” territory, and I hope it’s OK with you for me to do that. I briefly referenced it in my scattershot list of things that “adapted” does not mean, but I’ll go into it a bit more.

          One of my ongoing points here is to separate selection as we understand it scientifically from the myriad ways it’s assumed to mean other things, both inside and outside of biology as a discipline. One of those other things is a harmonious view of nature, or better, Nature . One may grant at least verbally that the events in question are all physical causes, but that they’ve been tuned via history into all-beneficial and generally beautiful systems. Cycilcity, stability, and equilibria all trigger our observer’s “like” buttons. It’s easy to assume that selection must be adaptation (in the aesthetic sense of “adjusting to”), and that this must mean accomodation. Or even improvement – that selection in action improves the conditions, life-experiences, and ecological outcomes, such that more cyclicity, more stability, and more equilibrium come about.

          However, these are assumptions – even projections. Plenty of ecosystems aren’t stable at all, particularly when you scale up or down to the time-span appropriate for the species you’re looking at. And to address the core point you raise about the rabbits, species longevity turns out to be the single most deceptive or if you prefer, disappointing variable of all to hang on the adaptation peg.

          Selection results in one thing: a measurable change in a given variable’s mean value, or a comparable metric. It may well result in a common, perhaps universal behavior which erodes or otherwise interferes with the chemical cycling in a given location. Up to and including interference which in the long run, reduces the species’ population size (which is a nice way to say, might directly lead to its collective demise in that location). There is nothing about an environment that “wouldn’t let that happen.” In Australia, the imported rabbits’ tendency to do that doesn’t have anything to do with them not being native.

          This topic is unfortunately under-studied and I suggest that’s because it hits us right in our projection-happy views. It’s OK to study mass extinction because those occur generally in the context of catastrophe – not only are there explosions, but an identifiable agent or agents “from without.” But background extinctions are disturbing to those illusions we like to sustain with a “nature’s way,” harmonious concept of selection and ecology, particularly now that we understand extinction is not “failed selection” or “restoring the balance” or any other such thing.

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