Sunday, 14 January 2018

Resource allocation theory

A common class of problems which agents frequently face involve resource allocation. Organisms divide their resources between growth, maintenance and reproduction.

Resource allocation decisions can be fixed or flexible. They can be directly genetically controlled or dependent on cognitive evaluation of circumstances.

To help quantify the resources involved it is often useful to split these problems up so that they can be represented as scalars and visualized on a one-dimensional axis. Seceral such splits will be described in the rest of this post.

First a few words about the "interchangability" of resources. Economists often treat resources as interchangable, since there is a market on which they can be exchanged for one another. However, not all organisms have access to efficient markets. Without these, it might not be easy to convert resources from one form into another. If resources are not interchangable at all doesn't make much difference to most of the analysis on this page. Instead of one resource, this just means that there are multiple resources which can be treated independently. However, in practice, resources may often be "weakly" interchangable, through barter, favors, debt, etc. Or maybe if you don't have enough sodium, you can make do with some potassium instead. While these kinds of complication are fairly common, they go beyond the scope of this page. Here we will just talk about "resources" as though they can be represented by scalars.

A fairly basic split when modeling resource allocation decisions is between self and other. Resources allocated to yourself are often then sub-divided between growth and maintenance processes. Other-allocated resources typically go into a range of processes associated with reproduction: mate seeking, courtship, coitus, parental care - and so on. It is possible to manipulate this self/other axis in a wide range of organisms via dietary energy restriction. This diverts resources into maintenance processes and away from reproductive processes.

Another fairly common way in which resource investment can vary involves the parental investment axis. Organisms face a choice between investing in existing offspring, or investing in producing new offspring. Strawberries, salmon and elms often focus on creating new offspring - while by contrast, elephants, whales and humans tend to invest quite heavily in their existing offspring. The parental investment axis is often referred to as r/K selection, which I rate as one of the worst pieces of terminology in evolutionary theory.

The parental investment axis seems rather neglected to me. Apart from the associated terminological mess, another issue is political correctness. When the topic comes up, it often gets mentioned that the human fertility rate is pretty variable. In Nigeria and Somalia is about 6, while in Hong Kong and Taiwan, it is about 1. After a while, Rushton (1996, 1988) may get cited and then this often leads to accusations of racism flying around. The parental investment axis seems to be a hot-button topic which is difficult for many people to discuss dispassionately.

Whether to invest in existing or future kids is one decision, whether to invest in existing or future mating partners is another, related decision. Males and females both face this sort of decision sometimes - their existing mate may be damaged, old or infertile. Or maybe they became more attractive and can find a better mate. Some female animals carry sperm around with them - for them the issue can be whether to use the existing sperm or to get a new stock.

Another resource-allocation decision involves whether to put resources into reproducing sexually or asexually. Not very many creatures face this dilemma, but strawberries, some aphids and some fish can reproduce in both ways depending on the circumstances. Reproducing asexually avoids the costs of sex - such as the costs of producing and spreading pollen or semen, but also avoids the benefits of sex, such as producing diversity to hinder the spread of parasites.

Resource allocation theory (and optimal resource allocation) also apply to cultural evolution. Indeed these terms are more common in economics than they are in traditional evolutionary biology.

In biology, this topic is often treated as part of life history theory.

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