09 June 2009

Nobody knows what behaviour is

The question seems easy. “What is behaviour?”

A new paper suggests that this question is fiendishly difficult.

I often tell people, “Behaviour is movement.” I actually don’t think that is an all encompassing definition, but it turns out to be a simple one that gives you a lot of mileage. So I freely admit my definition is quick and dirty and incomplete, but Levitas and colleagues crave something more... well, definitive.

Levitas and colleagues took a straightforward approach. First, they looked in the scientific literature: textbooks, articles, and so on. They claim that there is no consensus. Nevertheless, there are a few key words that crop up in their representative definitions, including “movement,” “response,” and “activity.” Admittedly, each of these words, and the definitions they are in, have different shadings. “Response” suggests something that follows an external event, apparently leaving little room for spontaneity. Still, things may not be quite as dire as the authors suggest.

Second, Levitas and colleagues surveyed members of three professional scientific societies. They had a series of examples that they asked questions designed to get at what people thought were the key elements of behaviour. For instance, people were asked whether or not they agreed with, “Behavior always involves movement” (cutting right to the heart of my definition!).

Then, they asked people to decide on whether certain examples were behaviour. For example, is “A rat has a dislike for salty food” a behaviour? Some of the questions have a strong teleological bent, saying what the behaviour is for. “A sponge pumps water to gather food” is one example.

The authors found no strong consensus in their survey results on either of these sets of questions. Nothing got 100% agreement, and nothing got 100% disagreement. Though I’m not sure how I feel that the statement, “behavior always involves movement” got the lowest approval, with just 7.6% agreeing.

Flying geeseThe example that had the highest agreement – 99.1% – on whether it was behaviour or not was, “flocks of geese fly in V formations.” But even here, the authors note a potential problem: 31% of those surveyed said only individuals can behave! So about 30% of the survey respondents must have contradicted their own definition.

And this is far from the only consistence problem in the survey results.

23 respondents that agreed with the idea that organisms other than animals do not behave also agreed that algae (non-animals) swimming up a nutrient gradient was an example of behaviour.

Of course, having gone through all this, the authors can’t resist a crack at the task that nobody else seems up to: coming up with a working definition of behaviour. Theirs is:

Behaviour is: the internally coordinated responses (actions or inactions) of whole living organisms (individuals or groups) to internal and/or external stimuli, excluding responses more easily understood as developmental changes.

I am not sure I like the emphasis on responses to stimuli, but I’ll leave it to others to pick apart this definition for now. The comments section is open!

And, if nothing else, I learned that there is a Society of Plant Neurobiology, which was one of the groups surveyed. That plants do not have neurons does not phase these people. And good on them.


Levitis, D., Lidicker Jr, W., & Freund, G. (2009). Behavioural biologists do not agree on what constitutes behaviour Animal Behaviour DOI: 10.1016/j.anbehav.2009.03.018


Neuroskeptic said...

I don't find this all that surprising. It's surprisingly difficult to define most words. The philosopher Wittgenstein famously asked what the definition of a "game" is (i.e. what it is about games, and only games, that makes them "games"). You'd think it would be easy, but try it...

AK said...

I'm not sure you can draw a firm line anywhere between cellular and organismal behavior. The actions of an individual cell are cellular behavior, but organismal development is an emergent phenomanon of many cells behaving. So is the concatination of neural activity that drives action at the organismal level.

Would you define the "movement" of an asteroid through space as "behavior"? A thrown rock? If not, I doubt you could say that "behavior is movement". As for behavior "always involving movement", what about freezing in panic?

I'd define "behavior" as a change of state initiated by the object doing the "behaving". (Consider Kuhn's observation that pre-Neuton, motion was considered a change of state, but not after. Most of the "motion" involved in "behavior" is also a change of state. And, yes, I realize that "continuing to stay frozen in panic" could be defined a "not a change in state", but that depends on whether you define panic as a state without an automatic end-point.)