Function, behaviour, and evolution

Yeast was used to show that evolutionary fitness can be predictable.

Some new research suggests that evolutionary fitness is predictable even if the route taken is not. This actually bears on the difference between function and behaviour, both in nature and in designed products.

Dr. Michael Desai at Harvard has done some very impressive work with the evolution of yeast. He has shown that the fitness of different lines of yeast is essentially the same. This means that even though the mutations that result in different strains are random, they all tend – after a sufficient number of generations – to result in populations that are equally fit. All evolutionary roads lead, as it were, to Rome.

I think this work is a very good demonstration of the difference between behaviour and function.

I’ve always thought of behaviour as the direct response or output of a system to direct stimuli or inputs. Exert a physical force on an object, and it will deform; shine a light on something, and it reflects some and absorbs the rest; add enough heat to something and it will change state (or even combust).

Function, on the other hand, is the role that behaviour plays in a larger system.  Deformation (and resistance to it) of objects means the object will contain energy; reflected light will make an object visible to some agent; combusting something will generate heat and energy that some agent can use.

There are many behaviours that can provide the same function. The behaviours of a teacher, a textbook, and a responsive website are all very different, but they all provide the same function – to “teach.”  Planes, trains, and automobiles all behave in different ways, but provide the same function of moving people and cargo.  Photovoltaics, nuclear power plants, and Lithium batteries all have different behaviours, but they all have the same function – to make electric power available.

I think Desai’s work shows the difference between behaviour and function in nature.  The fitness of his yeast strains are an indicator that the strains have all reached some stable functional niche within their environment.  The specifics of each strain, as described by the mutations that give rise to them, imply some behavioural difference in the biochemistry they carry out.

I find this pleasing, as a design researcher, because it suggests that there is a certain naturalness to the behaviour/function dichotomy.  That is, if there is a symmetry between how we model natural systems and artificial systems, it means we potentially have a universal framework for understanding reality.

That bodes well for systems thinking (of which the behaviour/function framework is part) as a universally applicable way of understanding the universe.


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