What is fitness in evolutionary biology?
In an earlier post it was pointed out that John O. Reiss argues that the fitness landscape metaphor has teleological implications. If evolution is anything close to the metaphor then the process is fundamentally teleological.
Reiss also makes the following interesting remark:
The rigor of this approach, however, is lessened because there is as yet no universally agreed upon measure of fitness; fitness is either defined metaphorically, or defined only relative to the particular model or system used. It is fair to say that due to this lack, there is still no real agreement on what exactly the process of natural selection is. This is clearly a problem.
He is right, it is a problem and the role that fitness plays in evolution is a hot topic of debate. There are at least two ways that scientists and philosophers view fitness. The propensity view of fitness argues that fitness is a probabilistic propensity while a statistical view sees fitness as a subjective probability. The propensity view sees fitness as a causal factor while the statistical view "deprives fitness of any causal or explanatory power".
It is an ongoing discussion and here are a view articles discussing the role of fitness in evolutionary biology.
Two ways of thinking about natural selection
Selection and Causation (argues against a causal view)
Fitness and Propensity’s Annulment?
Fitness (Stanford Encyclopaedia)
Matthen and Ariew’s Obituary for Fitness: Reports of its Death have been Greatly Exaggerated (argues for a causal propensity view)
What fitness can't be (argues against a causal view)
How do you understand the concept of fitness? An intrinsic propensity or disposition or potential of an individual and/or a population that plays a causal role in biological change over time? Or is it a subjective probability? Do you have any other interpretation of the concept?