Long ago, before my BioLogos days, I think even when I was still a real doctor, I saw a documentary on the hammerhead shark.
The scientist involved came to the conclusion that the weird bauplan of the shark can only have arisen more or less saltationally, and that the creature had had to learn an entirely new lifestyle pronto or die. Here’s a clip of what it had to learn:
Clearly such a learning curve would have had to involve the very first generation under such circumstances, because trying to hunt like a conventional shark whilst adapting its behaviour over generations wasn’t going to work. There would never be a second generation.
At the time, schooled in conventional Darwinian gradualism, I mocked this scenario. But in fact, given neutral theory and niche construction theory, it’s an entirely realistic possibility in theory. In that view the shape of the shark’s head, and its special senses, are (like all traits) controlled by combinations of vast numbers of genes, generated by near-neutral mutations, and there’s no reason why recombination or mutation could not suddenly generate a bizarre bauplan.
It’s comparable to the new finding that a person with a genetically very high risk of breast cancer, due to being dealt a “bad hand” of the many SNPs that combine to produce the risk, could nevertheless have children with an unusually low risk, by their inheriting a luckier mix of SNPs from both parents.
Niche construction theory takes this forward: the newborn shark, with all the instincts of former sharks-of-little-brain, suddenly finds itself with a head like a mallet, eyes several feet apart, and more sensitive senses. It will starve if it tries to chase fish in open water, but luckily, intent on survival at all costs, it hits on the strategy of stealth bottom feeding shown in the video.
Maybe this is a trick each generation of sharks had to learn – since adult sharks don’t stick around to teach their children. Or maybe it led to some fortuitous epigenetic change that was inherited until, eventually, it got hard-wired into the genome as we see today.
Now I’ve had a comparable discussion with Joshua Swamidass over at Peaceful Science just now, only in this case dealing with the diversification of the peregrine falcon and the hobby falcon over (it’s believed) the last 10 million years. Most of the changes over that time, Joshua says, will have been neutral.
Neither of us has been suggesting the kind of saltation proposed in my hammerhead shark documentary, so the learning curve has been nowhere near as sharp for the falcons. Nevertheless, the basic “neutral theory” process is that the majority of features a previous generation of Darwinists would have considered adaptive – the specialised wing profiles, the peregrine’s unique nostrils, and so on, are in fact near-neutral accidents that escape adaptive selection. (The peregrine nostril pic below is from a piece of mine with some relevance to the present subject).
And so niche-construction theory, when added to that, envisages a changed proto-falcon becoming maladapted to its habitual life, and adjusting behaviourally to the situation by becoming a stooping peregrine, or a dog-fighting hobby, or even a hovering kestrel, as the genetic changes dictate.
A more graphic example of this is if we similarly argue for a predominantly neutral evolution of whales from land animals (and why would one not?). The time frame is probably a million years or so shorter, and the changes far more profound. But with adaptationist gradualism abandoned, contemporary genetics allows for quite rapid and dramatic changes. These changes not being adaptive, it’s fortuitous that the feet disappear to become flippers, but the emergent whale has simply to shrug and give up coming up on land. That will be helped by finding its young do OK because of the changes allowing water-birth. Nostrils shifting dorsally turn out simply to strengthen the commitment to water – presumably any whales that developed a ventral blow-hole instead suffered purifying selection, since no existing whales have learned to swim upside down.
In all these cases, though, the one thing that must not, and apparently does not, change is the native wit of animals, and even plants, to change their way of life to fit the niches for which the gratuitous changes of neutral mutation render them suitable. This is counterintuitive, firstly because one would have thought that crucial behavioural skills, such as the hunting techniques of sharks or falcons, or the urge to return to land to breed for aquatic arterodactyls, would be pretty hard-wired. That hard-wiring, after all, is what falconers exploit to train them to sport, and it is species specific, as the training has to be.
There are celebrated cases where dogs or goats whose fore-limbs have not developed or been lost show a remarkable ability to learn to walk on their hind legs. But they’re always in protected human environments – even three legged goats in the wild are likely to succumb to falls, predation or just being out-competed by the normal kind.
Even so, there can be few more complex behaviours that the ability to recognise the new possibilities and liabilities of a new bauplan, so as to seize the opportunity to give up being, say, a generic falcon and invent a whole new set of behaviours and skills related to flying at 200mph and seeing sparrows a mile away or, alternatively, hobby-type skills related to outmanoeuvring swifts in their home-element at low levels.
It would seem, intuitively, likely that neutral evolution would mess with those adaptive skills even more than that it would change the entire shape of your head into a hammer and leave such skills intact. On the face of it, it’s a bit of a mystery why the ability to seek out ecological niches successfully should remain universal when everything else about you is up for random shuffling.
It takes a shift in perspective to see a Triceratops simply as a Protoceratops with more severe genetic syndrome, or an anteater as a sloth forced by corrupted anatomy to lick the ants off the leaves it once chewed.
But then I probably lack imagination, because I really can’t see the design of a peregrine falcon or a whale emerging primarily by mildly deleterious mutations. On the other hand their example of making the best of a bad job is kind of – inspiring…