Non-adaptive explanations as null hypotheses in Evolutionary Ecology
As a general rule, the Graduate Student tries with great conviction to avoid public humiliation. The Graduate Student will spend long hours in the isolation of his laboratory, reading his Advisor's doctoral thesis with furrowed brows, diligently applying the appropriate statistical tests to partially-failed experiments, and avoiding the departmental seminar coordinator as if she had Zaire ebolavirus. Most of all, though, the Graduate Student is motivated to plod along by the terror and anticipation of the Week of Reckoning: the annual (and sometimes mandatory) sojourn to a scientific conference.
|When is a non-adaptive explanation reasonable as null hypothesis?|
I am well-versed in this area, as I have first-hand experience. I was at a conference a number of years ago, as a Graduate Student (I suppose I am still a Graduate Student, as I haven’t actually received my sheepskin in the mail yet). There I found myself in discussion with a Well-Respected Member of my Field. The discussion was going well, at first, but I eventually found myself in an error-catastrophe loop. I was trying, with great desperation, to explain the predicted relationship between temperature and body size, and I eventually asserted that the negative relationship that I expected to observe was based on a physiological constraint that maps body size to rearing temperature… at this point the Well-Respected Member of my Field cut me off, furrowed his brow, and replied:
|Electrofishing for juvenile Atlantic salmon during my thesis research|
Before I recapitulate the conclusions I drew after being told “Everything is adaptive, if you go deep enough”, I should defend the use of parsimony in evolutionary ecology. My view is that parsimony is one of many useful tools that the evolutionary ecologist should keep in his toolbox. Certainly, a blanket application of parsimony in evolutionary ecology is unwise, as parsimony will be more useful in some cases, and less so in others. For instance, the use of “maximum parsimony” to generate phylogenies is reasonable because it assumes, rightly I think, that it is statistically less probable for characters to revert back to their ancestral state after undergoing a change (at least, this is my understanding).
|Atlantic salmon eggs vary greatly in size, and there's all kinds of adaptive and non-adaptive explanations as to why this is...|
I also believe that there is some value in developing and testing simple explanations before moving on to more complex ones. In a reductionist framework, testing ideas that incorporate the fewest assumptions will, I think, lead more frequently to an unambiguous result. A clear result can then inform a linear and logical development of an idea, such that knowledge is acquired by the systematic elimination of the unlikely and the impossible. In this framework, the foundation upon which an idea is based is sound, such that any extension of the idea is well founded. Admittedly, some might want to label this notion as something like “misguided idealism”, but my point is that we should think very, very carefully about the number and nature of our assumptions as we develop hypotheses. This is the motivation behind Burnham and Anderson’s information theoretic approach for model selection in hypothesis testing, and I see no good reason why parsimony should not also be a consideration while evaluating the merits of adaptive and non-adaptive hypotheses.
|Does the extent to which parsimony informs a null hypothesis depend on the scale at which the comparison is made?|
However, as Andrew alludes to, there might be far less consensus on what type of explanation is most parsimonious when variation in a mean phenotype is observed among populations of the same species. I think Andrew is quite correct here. Personally, I might venture, as Andrew does, that adaptive explanations are often most parsimonious in these cases, especially for life-history traits. But I think it ultimately depends on our understanding of the adaptive and non-adaptive mechanisms invoked, in conjunction with the demographic history of the population, etc. Thus, even if we accept parsimony as a useful tool in evolutionary ecology, I agree that it is not clear that non-adaptive explanations are generally more or less parsimonious at this scale.