Chapter 10 Adaptation, Perfection, Function Nicolas Crossley K Sex and Death Summer ‘05 E. Oberheim

Index –1. Definitions in Adaptionism: traits and functions –2. Methodological Problems and redefining adaptionist groups –3. The alternative theory –4. Looking for another methods for adaptionism Definitions - Methodological Problems - Alternative Theory - New Methods

10.1 Definitions: –adaptive trait: trait that increases the relative fitness of their bearers how to choose them? –adaptation: trait that has been selected by natural selection. –vestigial trait: relic of previous selection. –exaptation: trait used for a different purpose than the originally selected for. Definitions

10.2 Functions –etiological theory: asking for function is asking for evolutionary origins. –propensity theory: asking for functions is looking at adaptive effects of traits. No need to do an evolutionary history. –causal role functions: a functional analysis refering to a particular capacity (might be capacity to reproduce) Definitions

10.3 The attack on Adaptationism (Gould and Lewontin) –every useful trait exists because it is useful –every trait is explained by adaptation what features of an organism are its traits? –unfalsifiability Definitions - Methodological Problems

10.4 Defining adaptationism: –Empirical adaptationism: natural selection is the main factor in evolutionary history –Explanatory adaptationism: natural selection may not be the main factor, but it is the only mechanism that produces complex adaptation. –Methodological adaptationism: biological systems should be studied looking for a good design. Definitions - Methodological Problems

10.5 The alternative: Structuralism and the Bauplan –Each organism is designed as a variation of a basic plan. –Explanation by classification. –Darwin’s objection: earlier adaptation of common ancestors. Being useless, shouldn’t they disappear? Definitions - Methodological Problems - Alternative Theory

Developmental constraints and canalization: Process Structuralists –certain traits are essential in the development of the organisms, and therefore are not explained by the environmental pressure. –Highly conserved traits are strong attractors for development –Design space is smaller than adaptionists think. Definitions - Methodological Problems - Alternative Theory

The synthesis: generative entrenchment –similarities are common due to incremental design (probability of each stage vs the whole design) –the incremental design asks for the maintenance of previous modifications –Counter example: animals which modified their developmental trajectories retaining their similarities. Definitions - Methodological Problems - Alternative Theory

10.6 How to test theories: Optimality and Game models –Optimality models Fitness measure (measure of success) Heritability assumption Phenotype set (alternatives) State equations (interactions) –Game theoretic models interaction with others is also considered game matrix / strategies / payoff Instead of optimal strategies, evolutionary stable –can’t be invaded –fixed if everyone uses the same phenotypes Definitions - Methodological Problems - Alternative Theory - New Methods

Modelling to save the unfalsifiable –they are tested by their similarities with reality –Problems: depends on being able to independently test physiological and ecological assumptions mismatch is explained by problems in the factors and not in the modelling itself. –Heuristic value? Mismatch reveals unsuspected constraints –Adaptionism as a research program: adaption is ubiquitous, important and optimal. Core ideas not tested, “extra” theories are. Definitions - Methodological Problems - Alternative Theory - New Methods

10.7 Adaptation and the Comparative Method –The historical problem in testing adaptionist’s hypothesis Optimality is local Chance (drift) may have a big effect in small populations Modelling “best explanations” (abduction) require some historical assumptions –there are many “good explanations” Definitions - Methodological Problems - Alternative Theory - New Methods

Advantages: –test historical premises in adaptionist hypothesis low birthweight for hibernation. –test link between trait and habitat factors finding covariations (flightless bird in island) convergence –test the priority of selection history is constant selection gives the variance –Dunbar’s theory on brain size and group size Definitions - Methodological Problems - Alternative Theory - New Methods