Wednesday, January 06, 2021

Explaining Natural Selection

#evolution #adaptation .

Nature has two largely independent processes: one to produce variation (using mutation and/or sexual reproduction), and one to eliminate unfit variations (known as natural selection). What we observe at any timepoint in natural history is the emergent consequences of the interaction between these two processes. Over millions of years, overall biological complexity has increased, but a vast number of evolutionary paths have ended.

The long-term outcome of natural selection is often referred to as the Survival of the Fittest, the term introduced by Herbert Spencer, but this is at best a massive simplification, if not actually tautological. Darwin happily adopted Spencer's term in the later editions of his book, but Wallace argued that Elimination of the Unfit was a more accurate descriptor.

The actual mechanism of natural selection works in terms of reproductive advantage. Fit individuals (whatever that means) are likely to survive and pass on their genes to the next generation, while unfit individuals won't. Over time, the standards of fitness may gradually shift.

For example, if predators attack a herd of antelopes, the slowest are likely to be caught, while the faster ones will escape. The predators that are not fast enough to catch even the slowest antelopes will starve. Over many generations, thanks to natural selection, the average speed of both the antelopes and the predators will increase. (We're assuming here that the environment remains more or less the same. Obviously if the sea level rises and the plains get flooded, then the rules of the game change, and different variants will start to have the advantage.)

In order to survive, antelopes and predators don't need to be the fastest of their species, they just need to be fast enough. So we shouldn't take survival of the fittest literally - what this is really about is the survival of the fit.

And as Bateson argued, this term has a double meaning. This is not just about the survival of fit individuals or variants, it is about maintaining the relationship (the fit) between the two species.

 

During the Covid-19 pandemic, people have become interested in (and sometimes confused by) the way natural selection works among viruses. Professor Rickards spotted a misleading metaphor from the UK Government's Chief Scientific Advisor.

And Magnus Nordborg recently challenged a statement made in the Economist.

I commented that Natural selection is not about the survival of the fittest but the non-survival of the unfit. A deadly virus might not survive for ever, but don't hold your breath. @gcochran99 insisted that I was mistaken, and added

I think this is missing the point, for several reasons. Everything will change/mutate many times before anything ends up anywhere. While there seems to be one particular variant that is currently reproducing itself faster than other variants, new variants may well emerge with significantly different properties. Transmissibility depends on conditions that are not constant and at least partly under human control - including social distancing and wearing masks, as well as vaccines and other medical interventions.

And what I'm mainly arguing against is the idea that we only need to worry about the most efficient viruses because the less efficient ones will eventually disappear. Yes they might, but they might kill a lot of people and animals first. I made a similar point in my post on Viral Pandemic (April 2005). See also Arguments from Nature (December 2010).

In its small way, Gregory Cochran's tweet has gone viral, receiving more Likes than the rest of the thread put together. But that surely doesn't mean his tweet will end up being the one that matters.




P. den Boer, Natural Selection or the Non-survival of the Non-fit (Acta Biotheor 47, 83–97, 1999) 

Dean Keith Simonton, Creative thought as blind-variation and selective-retention: Combinatorial models of exceptional creativity (Physics of Life Reviews 7 (2010) 156–179 - paper recommended by @Tudortweet who writes: worth linking to the theory of creativity as another metaphor

Charles H. Smith, Natural selection: A concept in need of some evolution? (Complexity, Volume17, Issue3 January/February 2012) 

 See also: Delayed Success - Evolution (April 2023)

Updated 26 January 2021

1 comment:

  1. Yes, totally agree. This is a really important distinction between an almost teleological 'the virus wants to improve' view, and a general purpose 'humans as infrastructure' view - and reminds me of the story about two people trying to outrun a bear: one may not be able to outrun a bear, but it doesn't matter - they just need to outrun the other person.

    There are two aspects to evolution I think a lot of people miss, which might be of interest.

    1. People are actually really bad at understanding the complexity of 'suitability' which stems from a complex and dynamic environment, involving the external environment 'itself', but also all of the interactions between any actor within it (or, to a more extreme extent, both entities and the environment coexist as a network of interactions). People tend to simplify the environment to something understandable, eg 'animals want to get faster'. But it's not about being 'better' at something - it's about whether a *mix* of attributes (faster x careful x resilient x etc) is enough to survive. That makes *predicting* and *manipulating* evolution a lot harder as a more rational/conscious/scientific process.

    2. Evolution itself is not a constant - I don't have ready links here, but there are plenty of case studies where an ecosystem has been stable for quite a while, but then some change (small or large) can induce a rapid rate of change within the evolution of the ecosystem as they feed off (literally, as well as in terms of feedback) each other. (This is actually a good example: https://www.youtube.com/watch?v=BTPcq2HczVY)

    Again, the complex and (mathematically) chaotic factors involved here are difficult to predict or hypothesise. Maybe we can consider evolution itself as some sort of fractal or chaotic system and study it more as an emergent/three-body type area of analysis. Where genetic analysis of the covid virus family could be a newtonian approach, a systemic look at how they evolve and adapt in context of the (mostly-manmade) environment and our responses to it could be more like Boyle's law, simplifying the overall effects into easier-to-work-with formulae.

    What's missing from the covid discourse currently (at least here in the UK) is the big question of 'what matters to us?' - which sets the environment for which the virus will evolve. If we decide that reducing deaths matters (as seems to be the case?), then we deprioritise focus on long covid, or on track-and-trace, and we judge mutations in terms of morbidity. This, though, might mean that a less symptomatic, less fatal strain which avoids positive test results better might thrive. This _might_ be OK, or it _might_ be that the absolute number of deaths still increases, as lower proportion of higher infections trends upwards.

    What seems ironic is that we spend a huge of political power increasing both the surveillance power over individuals (eg access to individual data and metadata) and a huge amount of commercial power understanding and predicting complex group behaviour (eg targeted advertising based on common life patterns) and yet the approach to understanding the virus seems to be a hope that vaccines (née "herd immunity") will be all the answer we need.

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