The Handicap Principle (HP) is an obsolete idea proposed by Amotz Zahavi (Zahavi, 1975; Zahavi & Zahavi, 1997). While it was popular in biology it can be rejected as it has no theoretical or empirical support.

First, the HP has no theoretical support as all the arguments for the HP have been completely refuted. Honesty is maintained by condition-dependent trade-offs (i.e. by differential marginal cost and/or differential marginal benefit) and not by equilibrium cost (Számadó, 1999; Lachmann et al., 2001; Bergstrom et al., 2002; Számadó et al., 2023a). Grafen’s (1990) seminal modelling paper that claimed support for the Handicap Principle has been misinterpreted as a handicap model (Penn and Számadó 2020), despite the fact that it is a life-history trade-off model.
Second, the HP has no empirical support as all the evidence supporting the HP has been misinterpreted and the anomalous findings have been ignored (Borgia, 1993, 1996; McCarty, 1996; Moreno-Rueda, 2006; McCullough and Emlen, 2013, Askew, 2014; Thavarajah et al., 2016; Guimarães et al., 2017; see Penn and Számadó 2020 for review). Experimental results have been repeatedly interpreted as supporting the Handicap Principle, however they confused correlation with causation. Signals can be honest and costly; however this is not enough to show that signals are honest because they are costly. See the fallacy of ‘affirming the consequent’ (Penn and Számadó 2020).

Third, the HP has generated enormous confusion, due to mixing up proximate and ultimate levels of explanation (Penn and Számadó 2020). Proximate investment is a necessity of life. Morphological features and behaviours are selected for the potential fitness benefits accrued as a result of these proximate investments. Yet in the handicap literature, every single trait with a proximate investment (meaning all) were labelled as a ‘handicap’ ignoring the obvious fact these investments were selected for because of their potential fitness benefits they provide. This resulted in a gamut of ‘handicaps’ ranging from immunocompetence-handicaps to vulnerability handicaps (Folstad and Karter 1992, Vehrencamp 2000, Hurd and Enquist 2005). These so called ‘handicaps’ had no explanatory power other than acknowledging the fact that different types off signals need different types of proximate investments.

We argue that (Számadó et al., 2023b):
‘To avoid confusion, signals having metabolic or other physiological costs at the proximate level are better labelled as investments or expenditures, rather than costs or handicaps, and they cannot be assumed that they have fitness costs (handicaps), especially since increased investment may instead enhance their fitness benefits.‘
The Handicap Principle needs to be fully rejected. It has to be replaced with a Darwinian theory of communication. This new theory should be able to explain both honest and dishonest signals and it needs to be integrated into life-history evolution.

References

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