The building blocks of evolution

My brother and I were laughing about NASA’s weekly announcements from Mars that we’re getting ever closer to finding life there. If there isn’t any, of course, we’re not close at all. But they keep telling us they’ve found the “building blocks”, and we conjectured that the next press release will say life is more likely than ever because they’ve found its absolutely most completely fundamental building blocks on Mars – ie protons, neutrons and electrons.

Once our puerile chortles subsided, I got to thinking about what the building blocks of evolution are, and that maybe we’re too culturally conditioned in our assumptions. To Darwin, it went without saying that the individual organism was the basic unit of evolution. Depending both on Malthus and livestock breeders, it was clear to him that in the struggle for life it is only the fittest individuals that survive. A bird lays ten eggs – but only the strongest one or two live to pass on their variations. It’s those variations between siblings which power progress. But as good Prometheans we’re a pathologically individualistic society. A documentary about Stonehenge this week showed how suddenly the communal lifestyle and burials of its first phase gave way to the cult of the individual around 2500 BC. A similar, but more radical, shift occured at the Renaissance – showing that individuality is not a fundamental of the Universe (though that would probably be news to the “autonomous creation” TE boys).

Richard Dawkins, in contrast, took the unit of evolution down to the molecular level – the gene. For him, the individual organism is just a machine for the gene to propagate itself. Now that we are beginning to see how the genome is less a program or recipe than a database selectively employed by the organism, that conceit is less tenable than ever.

Yet the organism itself is a problematic concept in several ways. Its aim, in so far as one is allowed to talk of aims in biology, is said to be survival and reproduction. Yet in anything above the unicellular level, “survival” is quite a metaphysical concept, since many individual cells willingly undergo death for the good of the whole organism. This is clearly seen in somewhat disturbing cases like the adults that develop within the larval stages of echinoderms and then absorb them; but even the skin of my typing fingertips consists of epidermal cells that have died solely to provide protection to “me”. Who is me? My genome? But that’s just a database I use to build myself – including all those millions of cells I shed daily without a hint of remorse.

Then, of course, there are those creatures like polychaete worms whose egg-laying is accomplished only by their death. Being sexual, those worms are actually sacrificing their own genes for the sake of recombinations of them with other individuals’ sperm. In the same way the male mantis, often cited as an example of nature’s cruelty when it is eaten by its mate, is actually demonstrating that the unit of survival is somewhere beyond its own genome, to which higher good it willingly sacrifices itself in a way St Augustine would have applauded.

Kin selection has been offered as a way of explaining the origin of altruism through self-interest. If I die for my siblings, more of my genes will be passed on than if we all die. Yes, but less will be passed on than if the siblings die and I live – that Malthusian struggle, after all, was where we came in with Darwin. Nevertheless, the unit of evolution in that case becomes the family or clan rather than the individual.

But what about larger herds of herbivores, say gnu, that are interbreeding, but only loosely related to each other? They rely on vast numbers to survive and breed – but to survive and breed almost at species level. Predation is near-random – if I die, a bunch of nearby 5th cousin gnu will survive, which is very far from the individual struggle of an organism, still less a gene, to ensure its own genes win the day.

Another example: a fascinating TV programe recently showed how common frog tadpoles (Rana temporaria to you) respond to local pond conditions in individual ways (epigenetically, perhaps?) in their maturation, rather than according to genetics. That is a mystery in itself – how have they evolved not to evolve, but to vary reversibly to offer different responses to conditions that will change from pond to pond and season to season? That’s another question – but it’s obviously a clever trick. Who wants to evolve genetically and produce hundreds of eggs in your image that won’t survive a warmer year?

Be that as it may, one factor affecting their maturation is hormonal signals put out by other maturing tadpoles: they’re all giving out warnings that its high time to metamorphose – and they’re giving them not only to their sibling-tadpoles, but to those of all the other frogs in the pond that compete for resources. The Darwinian red-in-tooth-and-claw struggle is actually a cooperative community effort: “Hey guys, I’ve got a leg up to survive, and I’m passing it on to the rest of yous.” (“Gee thanks.” “Don’t mention it… we’re all in this together.”) Doesn’t give much of an example to the Eugenicists, does it?

Even this does not exhaust the possibilities for the “unit of evolution”. When one considers the intricate balance of forces within ecosystems (see here), in which individual organisms are sacrificed and yet the whole rich system prospers, why should we think this to be any less where life centres its efforts? Why focus at the level of the organism, apart from our addiction to reductionism and the historical baggage of Malthus and Darwin? After all, if we don’t see the death of our own skin cells as part of the bloody conflict of life, but instead as the harmonious working of our bodies, why shouldn’t we see the prodigality of the migratory salmon’s fatal spawning as a bountiful food source for an interdependent ecosystem, rather than as a lamentable waste of individual fish?

One could even take the whole biosphere as the fundamental unit of life and evolution, renewing the earth, as it has, for four billion years or so. There is no intrinsic reason why, say, green plants should not have poisoned the place for anaerobic organisms and thereby sealed their own death warrant (causing a total extinction event), instead of leading to the harmony we see in all ecosystems. The biosphere seems to have the same kind of checks, balances and feedback systems as the individual amoeba we watch gamely influencing its own destiny.

But that’s getting perilously close either to Gaia theory or to the suggestion that there is a benevolent God who creates wonderful order at every level out of tohu wa-bohu, so I’ll stop.

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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