Models of evolution

I remember at BioLogos a few years ago Dennis Venema doing a ballpark calculation that, given known mutation rates, he considered there was plenty of time for evolution, understood in Neodarwinian terms, to have produced all the mutations necessary for the differences between the chimp and human genomes since the time they are believed to have diverged.

You may have seen similar calculations for other controverted transitions, such as that from terrestrial artiodactyl to whale, whether that be based on the number of traits to be changed, or the genomic differences observed.

A thread at Peaceful Science looks at some work on whale evolution from a genetic angle, and Joshua Swamidass points out from this how even small mutations can produce significant and relevant changes, and not only that, but largely through the far more common loss-of-function mutations, rather than uber-rare creative ones:

It is remarkable how many of the changes required for whale evolution are caused by loss of function mutations (which end causing “pseudogenes”), or small tweaks to proteins. This is one of the big surprises of mammalian evolution. Large changes can take place with tweaks to the genetic code. Eyes adapt to underwater vision by losing a rhodopsin gene. Hind Limbs are lost with the loss of a homeobox gene. Taste buds are lost when two genes are lost. Smell receptors are almost entirely lost in most species too. In all these cases, we see remnants of the broken genes, and in many cases the details of how these losses increase function are well understood.

The process is too complex, and our understanding too small, to get too mathematically precise about what needed to happen, how it was done, and whether there was enough time for it to happen “naturally” (we don’t even have a real understanding of what we mean by “naturally”). But it does seem plausible to estimate that a checklist of how many things need changing between a hippo and a whale, or an ape and a man, or an okapi and a giraffe, and the millions of years available, might cause fewer logistical problems than some suppose, especially if we leave to one side our lack of a full theory of the development of form.

But it occurs to me that this is to look at the problem in a non-evolutionary way. I don’t by that mean that it’s teleological, as if evolution were aiming at a single goal – though it is still a fact that all the mutations necessary to tick off the list each required change need to arrive and be fixed by neutral drift or natural selection, be that underwater vision, a bigger brain, muscular carotid arteries or whatever. There certainly seems to be a teleological direction to any prolonged transition.

No, my problem is more that we tend to treat the transition initially as if it were a saltation, and then divide the changes necessary for that saltation into bite sized chunks, assuming that each modification is one step towards the goal.

But in fact, if we don’t hold to a theory of actual saltations, our beginning and end points are quite artificial. The changes needed are actually as many as are required to make a viable series of well-adapted species between our end points, each of which requires different novelties and the coordination necessary to make the species a well adapted whole. The more transitional species one proposes to have been buried, or lost, in the fossil record, the more numerically difficult the issue becomes.

For example, to use living species as analogues because we can observe their adaptations, for an ungulate to evolve into a deep-ocean baleen whale, it presumably has to go first via something otter-like, via something like a manatee, to a seal-like shallow water hunter, to some streamlined surface-hunter like a dolphin and so on. Each of these modern equivalents has its own world of special features, as any specialist naturalist will tell you. A seal may seem like a halfway house to a whale, but in most ways it is not (quite apart from having a different evolutionary origin). It is a fully-realized seal.

Neither is a medium-necked antelope a stage on the way to a tall giraffe, having acquired just a proportion of the necessary changes so far. Rather, its own genome and epigenome, control-networks, Orfan genes and non-genetic inheritance are tailored to being a particular kind of medium-height animal, neither a scaled down giraffe nor a scaled up okapi, but a specialist in its own niche.

One can imagine this better if we suppose Australopithecus to be a true transitional between our common ancestor with the chimp and ourselves. We assemble all we know about its anatomy, ecological niche and (per impossibile) somehow manage to get a good chunk of its genome from somewhere. I suggest that there would be a pretty much comparable number of morphological, genetic and behavioural changes to account for its difference from us as there are between us and the chimp. But then we could repeat the same exercise with the chimp-Australopithecus transition, with much the same result. But we now have something like twice the number of changes to cope with because, once again, Australopithecus is neither an upgraded chimp or a proto-human, but a fully adapted form different from either.

On another thread about evolutionary transitions, Joshua cited Zeno’s Paradox to me, in my view inapplicably. However, something like it seems to operate on any gradualist evolutionary scheme.

The philosopher Zeno argued that change was impossible, by imagining a runner who ran halfway to his goal, and then half of that again, and so on. He would never arrive, because the number of stages would become infinite. No gradualist, of course, believes in infinite gradations of evolutionary transition, though there has always been an implication that there are no true species, but only a continuum from ape to man, or whatever, lasting millions of years and containing very many more species than we now find in the record.

But in practice, it is assumed that there is enough stability for true species to split into daughter species, yet far more often than our cladograms are able to mark by known forms. But it is logically necessary that any evolutionary transition is also a transition through many real changes of environment and lifestyle occasioned by the animals’ particular forms. The number of changes for the sum of all the stages, not just the changes between start and finish, is what must be accounted for plausibly. The more the postulated tranitional species, the more the sets of changes to account for.

An illustration from engineering. I appreciate that such analogies are dangerous, because life is not machinery. Nevertheless, molecular evolution is very much an atomistic, mechanical approach to understanding life, and we know (and often care) too little about holistic systems approaches to be able to invoke them to deal with problems. So modifications in machines can, surely, be some kind of proxy for mutations in genes.

If we ask how Formula 1 cars have developed between the 1950s and now, we could make a list of the many things that have changed: aerofoils, carbon-fibre technology, slick tyres – a whole host of things, though a finite number. However, that would in the first place ignore the rule changes that have meant there was not a smooth continuum. There were many things that have been gained and lost that didn’t make it to our list – such as ground effect cars or anti-lock braking. These, and a host of other innovations that simply became superceded by other innovations, are part of the development story, and multiply the changes to be explained by orders of magnitude. In other words the cars did not just move along a continuum from “slower” to “faster”, but were designed for a large number of ever changing conditions.

Even so, such a list of “technological innovations” isn’t the biggest problem to be addressed. Racing cars are certainly a whole lot less complicated than living organisms, but keeping them competitive requires far more design changes than any list of engineering advances could possibly indicate.

In an article Zoe Chilton, from the Red Bull Technical Team, says that for them:

Succeeding in Formula 1 is now all about the cycle of racing, measuring, analysing, developing, and then continually repeating this process, head of Technical Partnerships at Aston Martin Red Bull Racing Zoe Chilton said, with the team producing somewhere in the range of 1,000 new designs between every race in the calendar, or 30,000 for the season.
“Everything we do is data driven,” Chilton told ZDNet. “It’s always about data, and it’s always about planning ahead.”
Data is gathered from hundreds of sensors spread out over its cars during testing and racing, compiling information on performance and conditions to inform changes that should be made to the cars or driving strategies.

Did you realise there are 30,000 design changes to an F1 car from start to finish of just one season? In most cases, none of the items from our list of innovations would even be involved.

Evolution, unlike the Red Bull team, does not plan ahead, so if there is any equivalence between the list of “design goals” we can make for Formula 1 cars or whales, and this huge number of “unseen” design decisions necessary to make the car succeed in a hostile environment, than the evolutionary process must either be a lot more efficient and busy than we think, or else very lucky indeed.

We don’t actually know if there are inbuilt “automations” in cell control networks that, independent of mutations and natural selection, somehow optimize the accommodation of any evolutionary innovation within the organism and its environment, rather like Darwin’s personified and idealised natural selection, constantly watching and improving like some auto engineer at its computer screen. Such a rosy vision of natural selection’s power is long gone, but if there are similarly powerful homeostatic mechanisms in living things, then they are far, far more intelligent than the data collecting in Formula 1, which requires human operators for whom “it is always about data, and it’s always about planning ahead.”

And such automatic oversight would certainly make evolution such child’s play to accompish that few problems would remain to engender doubts. But if they did exist they themselves would have had to evolve, somehow. And in any case I’m not aware that such mechanisms have been found, given the current emphasis on mildly deleterious neutral evolution, and beneficial changes from loss-of-function mutations with a sprinkling of natural selection.

If they were found and understood, they would surely constitute an entirely new theory of evolution – one that was almost irredeemably teleological.

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About Jon Garvey

Training in medicine (which was my career), social psychology and theology. Interests in most things, but especially the science-faith interface. The rest of my time, though, is spent writing, playing and recording music.
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