How could sophisticated mechanisms such as the flagellar motor or the adaptive immune system have evolved without some guiding hand? Henry Gee finds his answer to the argument of Intelligent Design in the lamprey.
We are accustomed to thinking of ourselves as peaks of perfection, and the arrangements of more "primitive" creatures as similar to our own, only cruder. It's a nice idea. Until along comes the sea lamprey to challenge our preconceptions.
Researchers have found that the lamprey (Petromyzon marinus) has a has a sophisticated system of adaptive immunity, that is entirely different to our own. Many organisms have a kind of natural immunity, but the adaptive immunity of mammals was supposed to be something special. By dint of a kind of controlled chaos, specialized parts of our genomes rearrange themselves to produce antibodies, custom-built proteins that are then selected to target any kind of foreign molecule the world can throw at us.
One of the great mysteries of immunology is how and when this remarkable system originated. For many years, immunologists looked for its beginnings in lampreys, sucker-mouthed creatures that represent the earliest flourish of vertebrate evolution more than 500 million years ago. Lacking jaws and paired fins, lampreys are almost as primitive as a vertebrate can get. They seem to have adaptive immunity, but scientists haven?t found even a glimmer of any antibodies.
There never was only one solution to adaptive immunity: thanks to the lamprey we now know there were at least two.
The discovery, reported by Max Cooper and colleagues in Nature this week, that lampreys have developed a perfectly respectable adaptive immune system all by themselves shows that the problem lies not with evolution itself but more with the way we think about it. Alas, we humans do not represent the pinnacle of design to which all other species aspire. Collins? work shows us, once again, that evolution experiments with various solutions to life?s problems, only some of which stay the course. There never was only one system of adaptive immunity: thanks to the lamprey we now know that there were at least two, and possibly many more, now extinct, or remaining to be discovered.
The fact that the work seems so surprising exposes another, more dangerous conceit that scientists are prone to. Dangerous, because it leaves science wide open to the temptations of so-called ?Intelligent Design?. Advocates of this view object to evolution by invoking what Richard Dawkins has called the ?Argument from Incredulity? ? that is, if I don?t believe that something is possible, it cannot happen. Philosopher William Paley in his Natural Theology famously used this argument when he compared the delicate designs of nature with a pocket watch. Pocket watches are not made spontaneously, so if the existence of a functioning, integrated watch implies a watchmaker, then the same must surely apply to a living creature.
More than a century later, proponents of Intelligent Design use the same reasoning when they marvel at the intricate design of, say, a bacterial flagellar motor. How can one ever give credence to the view that the sophisticated mechanism of the flagellar motor could have evolved to such precision without a guiding hand, when the tiniest of changes to its apparently irreducible complexity might render it useless?
I was discussing the problem with two polymathic friends of mine, reproductive biologist Jack Cohen and mathematician Ian Stewart, co-authors of Figments of Reality, Evolving the Alien and The Science of Discworld. They are working on their next book, Appearance of Design (to be published by Penguin next year) and Cohen sent me a draft chapter containing a devastating response to the challenge of Intelligent Design. It arrived on my desk at about the time that the work on the lamprey immune system was making waves in the Nature office, so it struck a particular chord with me.
A wide variety of flagellar motors have been described, each with its own solution to motion in the microworld.
Cohen argues that the fallacy in the Intelligent-Design argument about the flagellar motor (or any other system), is that proponents present the motor we see as The Motor, the exemplar, the only one possible, and, what?s more the best possible, surely optimized by a Designing Hand. But when Cohen searched the literature, he found that a wide variety of flagellar motors have been described, each arranged in its own way, each its own solution to effective rotary motion in the microworld. There is no such thing as The Motor, no Platonic perfection enforced on bacteria by Divine fiat. Instead we see ad hoc solutions that are not perfect, but idiosyncratic and eclectic ? just what you would expect if evolution were working on its own, without a Designer.
But before we as scientists allow ourselves to be too smug, we should consider how our own attitudes are over-welcoming of Intelligent Design. Generations of biologists and medics have gone through school and college being exposed to a parade of ?types?. We learned to dissect The Dogfish, The Frog, The Rat, as if each one was the only possible example of its kind. Diversity falls as an easy casualty of efficient learning, and grand generalizations of evolution are extrapolated from The Fly, The Worm, The Mouse and The Zebra-Fish.
Granted, this does make things simpler. But the unthinking adoption of this idea by many scientists gives the Intelligent-Design school an easy target and is the reason why concepts such as The Bacterial Flagellar Motor are not immediately laughed off stage.
The only way to gain a realistic understanding of how life works is to give students hands-on experience of the diversity that exists. I was lucky ? at school I trawled the countryside for natural history specimens, rocks and fossils, while at college I had hands-on experience of the outsides (and insides) of all kinds of exotica. But the triple tyranny of risk assessment, cost and politically-correct squeamishness has now seen off such activities for all but a few.
I believe that unless biologists have dissected real animals or experienced natural diversity for themselves, they are not worthy of the name. It was this same exposure that sowed the seeds of evolution in the mind of the young Darwin, turning him away from the theoretical, typological views of German Naturphilosophie that resonate still in those who argue for the presence of a designing hand. The artificial environment of the lab rat is as rarefied as the thoughts of Plato and Aristotle, the philosophy from which this idea derives. It no coincidence that it is in these very environments that Intelligent Design finds its most willing converts.
PancerZ. et al. Nature, 430, 174 - 180, (2004).
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Gee, H. The tyranny of design. Nature (2004). https://doi.org/10.1038/news040705-1
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