If someone commits the mereological fallacy, then he ascribes psychological predicates to parts of an animal that apply only to the (behaving) animal as a whole. This incoherence is not strictly speaking a fallacy, i.e. an invalid argument, since it is not an argument but an illicit predication. However, it leads to invalid inferences and arguments, and so can loosely be called a fallacy. However, discussions of this particular illicit predication, the mereological fallacy, show that it is often misunderstood. Many misunderstandings concern the use of this illicit predication in the course of discussions of understanding the mind/body problem. Our aim here is to provide an accessible overview through discussing common misconceptions of the fallacy. We also discuss how conceptual investigations of the relation between living organisms and their parts fit within the framework of modern evolutionary theory, i.e. inclusive fitness theory.
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Kenny (1984) used the term ‘homunculus fallacy’. He argued that ascribing psychological predicates to the brain invites the question of how the brain can for example see or remember something. Since it does not make sense to say that the brain sees or remembers something, Kenny argued that ascribing psychological predicates to the brain leads to the absurd consequence that one has to assume a homunculus in the brain. We prefer the term ‘mereological fallacy’ because the fallacy is about applying predicates to parts (not to an alleged homunculus in the head) of living creatures. This also clarifies why the fallacy extends to machines. Aeroplanes fly and clocks indicate time, but it makes no sense to say that the engine of an aeroplane flies or that the fusée of a clock indicates time.
We discuss an empirical example illustrating what is meant by ‘lifetime fitness consequences’. Visser and Lessells (2001) studied the effects of clutch size on the fitness of the great tit. In experiments they manipulated the clutch size so that the birds had to raise two extra chicks. There were three experimental conditions: either (1) two extra nestlings were added to the nest, or (2) two extra eggs were added to the nest, or (3) the female was induced to lay two extra eggs (by removing the eggs of the clutch so that the female laid new eggs, and then adding the old eggs to the new ones). The effects of these manipulations were that in all conditions the tits raised two extra tits (i.e. four tits instead of two). The results of the experiments showed that the number of young who survived to breeding age did not differ between the three conditions. Hence if we were to calculate the fitness-effects during one breeding season, there were no significant effects. But there was a difference in fitness-effects when the next breeding season was taken into consideration. Visser and Lessells found that the manipulations affected female survival. Females in the third condition who experienced the extra costs of laying two extra eggs (besides the costs of having to incubate them and to raise the chicks) had the lowest survival. Hence if we calculate the life time fitness of the individuals, then we have a different result compared to calculating the reproductive success per brood (illustrating why lifetime consequences matter).
Boomsma’s ‘monogamy hypothesis’ should not be confused with Hamilton’s ‘haplodiploidy hypothesis’. Hamilton argued that haplodiploidy should facilitate the evolution of altruistic helping. However, studies have shown that is unlikely that haplodiploidy was an important driver of eusociality, while there is evidence that monogamy has played a key role (see further Gardner et al. 2012).
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We thank two reviewers for their comments on an earlier draft of this paper.
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Smit, H., Hacker, P.M.S. Seven Misconceptions About the Mereological Fallacy: A Compilation for the Perplexed. Erkenn 79, 1077–1097 (2014). https://doi.org/10.1007/s10670-013-9594-5
- Multicellular Organism
- Nonverbal Behaviour
- Inclusive Fitness
- Conceptual Investigation
- Teleological Explanation