I was fascinated by this article on the general nature of how life survives on this Earth, from NewScientist (23 March 2019, paywall) and Bob Holmes, which revisits the Gaia hypothesis of the biosphere as a living organism, and how life keeps going:
As far as we know, Earth is a one-off: there is no population of competing, reproducing planets for natural selection to choose between to form the next generation. And yet, like a superorganism honed by evolution, Earth seems to self-regulate in ways that are essential for life. Oxygen levels have remained relatively constant for hundreds of millions of years, as has the availability of key building blocks of life such as carbon, nitrogen and phosphorus. Crucially, Earth’s surface temperature has remained within the narrow range that allows liquid water to exist. It is true there have been upheavals: during a “snowball Earth” episode about 700 million years ago, for example, almost the entire surface was frozen. “But the key question is, why does it spend so much time in a stable state and not just flying all over the place?” asks Tim Lenton at the University of Exeter, UK.
This question has stumped earth scientists since James Lovelock first proposed the Gaia hypothesis in the 1960s. There is, after all, no obvious way for such self-regulation to evolve. This is particularly true because the processes that underpin Earth’s temperature, oxygen levels and the like – which include things like plate tectonics and erosion – operate over millions of years. That is far too long for the adaptation of individual organisms to their environments through natural selection to make a difference. This conundrum has led most evolutionary biologists to entirely reject any notion of Gaian evolution. “You simply cannot get an adaptation at the planetary level,” says Charles Goodnight at the University of Vermont.
But there might be another way, says Lenton. … he suggests, Earth and the early life on it might have interacted haphazardly at first. Unstable configurations – those, say, with little or no cycling of key elements such as nitrogen – would have failed quickly, requiring life to reboot nearly from scratch. Eventually, though, the system must have stumbled on a stable configuration, with better cycling and tighter regulatory mechanisms. It should be no surprise, then, that the planet of today has strong regulatory systems.
Sure, a sort of evolution of competing processes. Those that don’t make the grade are discarded, taking their dependent species with them, while those that are successful work to make Earth / Gaia a more stable place.
While the idea of evolution was originated to explain the origin of species, to borrow a phrase, there’s little reason to confine it to a biological context, as many before me have pointed out. To see it operate, a critical metric, measuring success, must be identified, and something that can change and affect the current result on that metric must be available in the entity that is evolving. Call that a variability component.
In biology, the metric, as a first stab, is the reproductive success rate of qualified members of a species, and the variability component is the fact that a species is made up of individuals, at least some of which include a reproductive function which includes variability in the next generation, which results from how DNA from contributors forms, and DNA’s vulnerability to mutation from environmental radiation and other contaminants. As the success rate moves towards zero, the species moves towards extinction, while a success rate that is increasing would appear to be moving away from extinction. However, because of the necessary interactions with the environment which feeds the species’ individuals, or the ecological web, to use the terminology of a previous generation, there is necessarily a positive feedback loop. Think of the population dynamics of wolves and deer. The two follow each other in their endless sin waves. This is a feedback loop. A species which is experiencing extreme success runs the risk of exhausting its environment, aka overpopulation.
And so an increasing success rate may simply presage a coming crash and near-extinction level event. See Peter Turchin’s Secular Cycles.
I must say, there’s quite a satisfying click! in my head when reading about these sorts of things, because, for those of us who like to understand this sort of thing, this really enlightens our understanding of how we came to be – and how, if we’re not careful, how rough the ride might become. Processes that are not area-specific make it easier to understand what’s happening in the world, once we get ourselves properly fitted to see them.
