From whence does purpose arise? People always want to know why: What is the purpose? Why did hurricane Sandy hit New York? Was it punishment for past sins? The idea of purpose is so central to people’s thinking that we want a purpose for every happening. This was engrained in philosophy as Aristotle’s final cause. Aristotle regarded the final cause as the most important of his four causes and it became central to medieval philosophy. Understanding the final cause has, indeed, been important to our survival. It was important to know the reason for the lioness taking a stroll. Was she just doing it for exercise or was she looking for a meal? If the latter, it was very important to give her a wide berth. Similarly in social interactions, it is important to know the purpose behind a person’s behaviour. Are they just being nice or do they have ulterior motives? And if so, what?
Purpose or Aristotle’s final cause is entirely from the physical sciences and downplayed in science generally. This leads to an argument against evolution. Evolution by natural selection has no purpose but is a stochastic process with the direction of each step being independent of the previous step and depending only on the local conditions at that moment. Apes did not evolve to form the stock from which humans later arose but rather humans arose as a result of local environmental pressures on the ape. The precise argument against evolution by natural selection is that since natural processes have no purpose, purpose could not have arisen unless there was an outside agency to give purpose. Since purpose is seen, for example in animal and human behaviour, such an outside agency must exist. If evolution produced this purpose, it must have been guided by an external purpose and not be due entirely to natural selection.
This argument is a prime example of proof by lack of imagination. It relies on not having enough imagination to find a method for purpose to arise from natural selection. Hence, the precise argument against evolution can be stated as: I can imagine no way that purpose can arise except by an external agency, therefore evolution must be caused by an external agency. The counter to proof by lack of imagination is the just so story. That is a story made up to explain a given occurrence without any evidence of wide spread validity. Generally, I regard just so stories as uninteresting and certainly not science. To make the just so story science, one would have to use it to make testable predictions. But as a counter to proof by lack of imagination, that is not necessary. All that is necessary is that to provide one plausible counter example. I will now give a just so story to counter the argument in the last paragraph.
So, let’s see how the illusion of purpose, if not purpose itself, could arise. Consider some bacteria in a solution with a gradient for food. The bacterium that moves towards more food will on average produce more offspring and therefore the population will eventually be dominated by those that move up the gradient. The resulting behaviour appears to have a purpose: namely to get more food. However, it is just the response to the local conditions, conditioned by evolution’s feedback loop.
One can apply the same type of reasoning to more complex situations and in every case evolution favours those individuals whose behavior appears to have purpose. Consider the case of a bird building a nest. Birds that build nests that do a better job of protecting their young will have more offspring (balanced somewhat by the cost of building the nest). Similarly with the behaviour of young men courting young women (and vice versa). Those that are successful produce offspring while those that aren’t, don’t reproduce. Thus, the behaviour seems to have a purpose but in fact, it is only that those who behave in a certain way leave offspring and hence, the behaviour is all that survives. Incidentally, this also explains why there are so few geeks.
Thus, we see that purpose, or to be more precise, the illusion of purpose, can arise from the feedback loop in evolution. Evolution favours those behaviours that work towards the end of producing more offspring, which is a purely mechanical process. But saying purpose is an illusion is perhaps going too far. In building models of animal and even plant behaviour, purpose is a useful concept that makes the job easier. Models that include purpose are simpler and make better predictions than those without and even if they didn’t, we are human after all, and do enjoy a just so story. Purpose, like the nucleon, is an emergent property that arises from the underlying dynamics. So the next time you are pursuing a member of opposite sex with a definite purpose in mind, remember that purpose is, if not an illusion, just an emergent property.
 See the blog http://www.quantumdiaries.org/2011/12/16/can-science-answer-the-why-question/ for more discussion.
 They can however be entertaining.