Friday, 13 June 2014

Proximate and Ultimate Explanations

Proximate and ultimate explanations are among the first terms that you learn about when studying ethology. These terms are used in other contexts, in addition to the study of behaviour, where they mean slightly different things, so it's important to understand them and not get them confused.

Why does an animals behave in a certain way? An animal's behaviour can be explained in proximate and ultimate terms. Proximate explanations deal with the 'how' of a behaviour i.e the underlying or mechanistic reasons behind a behaviour. Ultimate explanations deal with the 'why' of behaviour i.e the usefulness of this behaviour to the creature and how it came to acquire it.

Here's an example - birds singing in spring.

Proximate questions - How do birds manage to sing in spring?
Proximate answers - Daylight induces changes in hormones which make them sing. They learned to sing when young.

Ultimate questions - Why do birds sing in spring?
Ultimate reasons - For mating/reproductive value. The vocal chords of distant relatives and extinct birds indicate that this trait evolved concurrently with overall fitness.

It is important to realise that proximate and ultimate reasons are both explanations for the same behaviour/phenomenon but from different perspectives. You could say that proximate explanations provide the reasons underlying behaviour (what is it due to?) while ultimate explanations look at the bigger picture (what is it for?)

Proximate behaviours usually provide mechanistic reasons for behaviour or describe the 'triggers' behind behaviour. You can think of them as being the result of things occurring in the animal's body (e.g. hormones, nervous system, genes, age) or immediate environment. Proximate explanations can be further divided into mechanistic (causation) and ontogenetic (developmental). 

  • Mechanistic explanations (how does it work? how was it caused? what caused it?) usually deal with processes within the body that follow simple rules, like neurons and the nervous system, hormones, pheromones and other bio-chemical processes.
  • Ontogenetic explanations (how did it develop?) cover behaviour from the nature-nurture or gene-environment angle. These explanations build on mechanistic processes, and relate them to what's going on with the individuals environment, like learning or other aspects leading to behavioural development.

Ultimate explanations usually describe the function of a behaviour in terms of evolutionary history and function. Ultimate explanations deal with evolutionary benefits of a particular behaviour. These can be further divided into phylogenetic (evolutionary history) and adaptive (functional) explanations. 

  • Phylogenetic explanations (how did it evolve?) deal with why this behaviour might have evolved over successive generations instead of being lost. We look at the evolutionary history of the creature to see how natural selection worked on this trait. 
  • Functional explanations (what is it for? what purpose does it serve?) deal with the benefit the behaviour confers to the individual in terms of its current environment. It is important to remember that an individual can have a current trait that is adaptive without it being an adaptation. 

Here's another example - Honeybees swarming (splitting up and building new colonies elsewhere).

Proximate questions - How to honeybees manage to swarm? What factors lead to swarming?
Proximate answers - Because of the way their central nervous system responds to other bees doing the waggle dance. Or because this behaviour is triggered by colony size, brood comb congestion, worker age, or the queen having reached her maximum egg laying rate.

Ultimate questions - Why do honeybees swarm?
Ultimate reasons - For reproduction, survival, more food resources.
And one more - birds building nests.

Proximate questions - How does a bird know how to build a nest?
Proximate answers - It could be a genetically programmed or learned behaviour.

Ultimate questions - Why does a bird build a nest?
Ultimate answers - Because a nest assists in mating and so improves reproductive success, which means genes are passed on to the next generation.