Blute Blog

Blute's blog about evolutionary theory: biological, sociocultural and gene-culture.

Posts Tagged ‘density-dependent selection

Density-dependent natural selection may have implications for the coming decline side of the COVID-19 pandemic

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Chapter 3 of Darwinian Sociocultural Evolution on “Necessity: why did it evolve” discussed principles of evolutionary ecology, notably density dependence relative to resources in section 3.3.1., and applied them illustratively to the sociology of science. Subsequently Blute (2016) reviewed the history of, and greatly extended the theory. The extensions included its applicability to selection in space and/or time, to somatic functions as a cause and not just an effect (as in Fisher’s sex allocation theory for example), and to selection within and between, not just growing populations, but also declining ones. These may have implications for the coming declining side of the COVID-19 pandemic.

Where/when density measured in cost per capita relative to resources is low within a population, or in growing populations with a history of catastrophes, natural selection favours spending on consumption (eating and excreting) whereas where/when it is high or in declining ones with a history of bonanzas, selection favours investing in digestion (breaking down and building up). What should be built up? In a homogeneous environment it is mechanisms of social interaction whether cooperative, antagonistic or a mixture of both but in a patchy environment it is mechanisms of dispersal in time (maintenance), in space (motility), and/or in niche (mutability) – the 3 M’s. Similarly, low density measured in frequency or in growing populations with a history of catastrophes, natural selection favours production (many small offspring) whereas high densities or in declining ones with a history of bonanzas, selection favours “reproduction” (fewer larger offspring, ones capable of social interaction or their own 3M’s).

Both these somatic and reproductive distinctions are quantity versus quality ones with the former in each case depleting and degrading the external environment while the latter depletes and degrades the internal environment. As well, the former in each case is associated with a small size because of the disproportionate surface to volume ratio there and the latter of each associated with a large size because of the disproportionate volume to surface ratio there. Under the simplest set of conditions if both somatic and reproductive functions utilize the same or positively correlated resources and the two functions interact synergistically, then at low densities the more one consumes the more one can produce and vice-versa whereas at high densities the more one digests the more one can reproduce and vice-versa.

What then of COVID-19? Our culture is coevolving in interaction with their genes (gene-culture or culture-gene coevolution, between species in this case) and our culture has evolved favouring social distancing etc. in some places – depleting viral resources and causing a levelling off and decline in the viral population(s).  But our culture is now on the edge of reversing itself at least somewhat. What are the implications of that for the virus? Given that surely humans are a heterogeneous environment, selection on the viruses should then favour:
i) maintenance: those which live longer (e.g. making the recovered or infected but symptom free contagious for longer)
ii) motility: those which move further (e.g. placing themselves in small droplets which disperse further rather than just in large drops which tend to fall) and/or
iii) mutability: those which increase their blind mutation rate seeking a new niche (e.g. infecting organs other than respiratory systems such as kidneys, nervous systems etc.)

It is at least possible therefore that changes in their genes and not just in our culture will in the future be contributing to one or more further spikes in the pandemic until a vaccine is widely available or until the 70 or 80% infection rate required for herd immunity is reached.

Blute, Marion. 2016. “Density-dependent selection revisited: Mechanisms linking explanantia and explananda.” Biological Theory 11(2) 113-121.

Written by Marion Blute

May 3, 2020 at 4:22 pm

Resource depletion and environmental degradation

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I have suggested (e.g. in Darwinian Sociocultural Evolution Chpt. 4 and this blog, Evolutionary Myth 8 posted in August 2010) that resource depletion and environmental degradation do not necessarily go hand in hand as is commonly thought. Specifically, I argued that low densities relative to ecological resources favour consuming/producing more and are associated with small sizes and resource depletion, while high densities favour digesting/re-producing more and are associated with large sizes and environmental degradation. (The size association is because of the greater surface area/volume ratio useful in the former case and the greater volume/surface area ratio useful in the latter case). The associations however can vary depending upon how the four terms are further interpreted. Hanging out sometimes with philosophers who are experts at analysing concepts, including scientific ones, encourages one to pay attention to and dig out these kinds of distinctions.

Consider only somatic functions as illustrated in the abstract in Figure 1. If consumption is understood as eating and excreting more (outer arrows 1 and 2) while digestion is understood as breaking down (degradative metabolism) and building up (biosynthetic metabolism) more (inner arrows 3 and 4), then sizes should be as stated – small versus large, but the former deplete and degrade the external environment while the latter deplete and degrade the internal environment. On the other hand, if consumption is understood as eating and breaking down more (left arrows 1 and 3) while digestion is understood as building up and excreting more (right arrows 4 and 2), then depletion and degradation should be as stated with the former depleting (the external and internal environments) and digestion degrading (the internal and external environments) but both sizes should be intermediate (although cost differences could shove both smaller or larger for example). An analogous break down can be applied to offspring production and re-production.

Such philosophical analysis of concepts can potentially be theoretically useful in the scientific sense. For example, the different interpretations described can be understood not just as different ways of analysing concepts, but as different ways in which genes specifying different components of life history strategies may be linked differently. For example, as originally suggested, the first breakdown could characterize heterospory or proto-genders with anisogamy while the second could characterize homospory or mating types with isogamy.

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Written by Marion Blute

June 15, 2011 at 1:55 pm