Trends in Evolutionary Thinking

Blind Cavefish
Blind Cavefish. Pink, somewhat translucent blind cavefish that give evolutionary biologists palpitations.

Update: Still totally swamped at work (and, since our company serves companies that finance equipment used by business, this may be a very positive leading indicator of economic activity – this is not an offer to sell, nor a solicitation of offers to buy, and so on and so forth…). Having to be content to fire off short posts that don’t involve reading more books or doing any research. Will get back to that kind of stuff soon, assuming our customers deign to allow me to take time off at Christmas.

When I read the Selfish Gene and the Extended Phenotype, Dawkins’s conclusions seemed obvious and bit tame to me. Dawkins gives this big wind-up to the second book, about how it represents his original contributions to the field, and my reaction was: didn’t everybody get, from the first book, that genes would necessarily, in their expression as physical traits and behaviors, interact with the other genes? That my genes would necessarily interact with the genes of every other creature in my environment – in fact, that the sum of those interactions is what a biological environment IS? (Mechanistically speaking, of course.)

I guess not. Further, I thought Dawkins stopped a little short – I thought there were things he should have said, as obvious conclusions based on his premises, that he did not say. (NOTE: not saying that the observable evidence supports these conclusions – although I would be personally surprised if they didn’t – but only that the logic explained in the Selfish Gene requires them.) For example:

– After a couple billion years of evolution, one would expect a given genome to be carrying around lots of genes  that have proved advantageous in the past, but may not at the moment be expressed. (Using the term gene philosophically to mean that by which phenotypes are expressed and traits passed on, not the mechanical meaning used in gene sequencing as of a  particular set of molecules)

Given the above, this set of formerly useful but not currently expressed genes is subject to the same selection pressures as any other gene – does it cost more to carry it about than it is worth? The cost can be very low, that much should be obvious, so many genes will hang around because it’s cheap, survival wise, to keep them. But what about the benefits? Are there any? Couple ways to look at this:

–  Hybrid vigor is an adaptation. In the careful balancing act of gene expression, where certain genes are switched on or off in certain sequences to produce proteins that produce, ultimately, physical traits and behaviors (a process that we’re only now beginning to understand), could it be that rolling the dice and allowing for greater variation when the environment has been disrupted is a winning strategy?

Note when hybridization generally happens:  when the environment has been seriously disrupted by the introduction of another breeding group with which an existing breeding group has long been separated. On a chemical level, this means that there may be variations within each population in the mechanisms that control gene expression, so that, upon hybridization, much more variation occurs, as the controls behave differently in heir new ‘blended’ environment or perhaps are merely less efficient in suppressing variation.

So, when hybridization occurs, one would expect more variation in phenotypes: bigger, stronger, smarter – and, perhaps, smaller, weaker, and stupider. Here’s the key step: the environment has been disrupted – that’s how the hybridization was able to happen in the first place – meaning that niches are opening, closing, being established. Some of these variations might well survive better in the new niches than either of the original phenotypes from which the hybrid variations were created. The bald fact that hybridization has taken place means that the environment has changed, and all bets are off as far as how well adapted the old forms will be to this new environment.

The final piece: this process – the disruption of an environment by the introduction of a breeding group different from the closely related breeding group already there – has been going on constantly for over a billion years. Winners and losers have been selected in hybrid environments hundreds of billions of times. Using Darwin’s fundamental insight – that small pressures consistently applied can create real changes – it would be shocking if hybrid vigor were not an adaptation.

Circling back: therefore, we should expect that, among the ‘useless’ genes (in the philosophic sense), there would exist those which have proven useful to survival in hybrid situations.  Let’s take people, for example: many human hybrids are bigger, stronger, and more physically attractive than the average person from either group.  Given how humans tend to behave, these sure look like traits that would better help individuals survive in the new, likely to be socially chaotic, environment.

– Second – this is what triggered this brain dump – what about situations where the environment has been disrupted in some other way? Where, for a given species, traits that had helped them survive in the past are no longer relevant, and traits that are desperately needed are only partially present?  In this case, little fish got washed into caves a few thousand years ago – and promptly went blind (no eyes), lost all skin coloring, and got real good at finding stuff in the dark.

The question never asked in the article: how often does it happen that fish will end up in caves and not be able to get out? Because, if it’s a common enough occurrence, we would expect that, just as with hybridization, genes would be preserved which had proved useful in such situations in the past.  These genes function by producing proteins. Therefore, the presence of proteins that affect the phenotype of individuals is not a new idea in concept, although the researchers here seemed surprised to find it working as it is claimed it is working.

The article focuses on a particular protein, which acts to ‘keep in check’ a species’ genetic mutations.*

Cavefish underwent a process called “standing genetic variation,” according to study researcher Suan Lindquist, who has extensive experience in the subject. During less stressful times, certain species’ pool of genetic mutations are kept in check by a protein called HPS90. Dramatic circumstances, however, can deplete the protein and leave the organism open to all of its genetic possibilities. In the case of the cave fish, as Lingquist and fellow researchers proved in this study, stress triggered the right genetic expression — or at least triggered the right genetic expression in enough fish, Laboratory Equipment reported.

Be this as it may, this scenario fits perfectly under my more general claim – that organisms carry around genes that are only comparatively rarely useful, but are very useful once in a while. Those once in a whiles include hybridization – and fish getting washed into caves they can’t get out of. In other words, life has evolved to evolve; organisms carry around within themselves the genetic materials that allowed their ancestors to survive in very different environments, on the Aristotelian principle that anything that has happened is possible – that if your ancestors got washed into a cave and survived, you, too, have a non-zero chance of getting washed into a cave.

Fish have been around a couple hundred million years; rivers and caves for considerably longer. So, we can expect that, over time, billions upon billions of fish have gotten washed into millions of caves – and that some small percentage survived. Some of the offspring of those species managed to get washed *out* of the caves, where, presumably, some survived – and passed on the genetic capabilities found useful for survival in caves. So, today, hundreds of millions of years and billions and billions of fish into this process, we have some fish which, when washed into caves, are genetically predisposed to survive and reproduce. This survival involves gaining the necessary and shedding the expensive but unnecessary – they lose eyes and skin color, and their already superb ability to navigate blind becomes, perhaps, enhanced. (Fish in general aren’t exclusively dependent on sight – water is often murky and darkness falls every night.)

This is nothing more than evolution by means of natural selection at work across a longer time-frame than an individual lifespan. It can work across many lifespans, so that traits that are useful about every thousand years, for example, will be preserved if they don’t cost too much. That’s where I wish Dawkins had taken it.

* ?! This sort of wild speculation makes me feel I ought to just don the Sacred Lab Coat of Science! and proclaim my untethered amateur speculations THE TRVTH! They’re as good a theory as any, and have as much empirical support as most. How, even in concept, could one validate the theory being expressed here? And there’s no evidence they even tried – they played around with some proteins in a lab, maybe dissected a few fish – and make a global claim about evolution? Science is hard, after all, in the sense of difficult and harsh. Further, I can’t let the claim that ‘psychological stress’ activated this process pass – we’re now studying the psychology of fish? Pull-ease!)


Author: Joseph Moore

Enough with the smarty-pants Dante quote. Just some opinionated blogger dude.

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