The Unity of Fitness

Abstract

It's been argued that biological fitness cannot uniformly be defined as expected number of offspring; different mathematical functions are needed to define fitness in different contexts. Brandon (1990) argues that fitness therefore merely satisfies a common schema. Other authors (Ariew and Lewontin, 2004; Krimbas, 2004) argue that no unified mathematical characterization of fitness is possible. I focus on comparative fitness, explaining that it must be relativized to an evolutionary effect which fitness differences help to cause. Thus relativized, comparative fitness can be given a unitary mathematical definition in terms of probabilities of producing offspring of various types and probabilities of producing various other effects. Fitness will sometimes be defined in terms of probabilities of effects occurring over the long term, but I argue that these probabilities nevertheless concern effects occurring over the short term.

Levels, Time and Fitness in Evolutionary Transitions in Individuality

“…This has led Beatty & Finsen (1989), Sober (2001), and more recently Abrams (2009) to propose a distinction between short-term and long-term fitness. Although they all consider that short-term and long-term reproductive outputs are fitness, it should be clear by now that my view is that they represent different proxies of fitness.…”

Populations and pigeons: Prosaic pluralism about evolutionary causes

“…9 This is not quite correct if we step back from the idealized contexts discussed here. Abrams (2009bAbrams ( , 2009c argue that fitness is relative to a choice of an interval of time over which generational change takes place. In particular, describing an evolving population in terms of different intervals of time-or different numbers of generations-can reference different causal facts, and change whether it's appropriate to describe the population as undergoing selection.…”

Distinguishing Natural Selection from Other Evolutionary Processes in the Evolution of Altruism

“…Although the assumption that fitness is a reproductive output is very limited in scope, it will be sufficient to expose the problem of altruism in the next section. The more sophisticated notions of fitness that can be found in the literature (e.g., Mills and Beatty 1979;Bouchard and Rosenberg 2004;Bouchard 2008;Abrams 2009; Godfrey-Smith 2009) will not undermine the main points of the paper.…”