To mask, or not to mask, Alice and Bob's dating dilemma

AO_SCPLOWBSTRACTC_SCPLOWFace masking in current COVID-19 pandemic seems to be a deceivingly simple decision-making problem due to its multifaceted nature. Questions arising from masking span biomedicine, epidemiology, physics, and human behaviors. While science has shown masks work generally, human behaviors (particularly under influences of politics) complicate the problem significantly given science generally assumes rationality and our minds are not always rational and/or honest. Minding minds, a legitimate concern, can also make masking legitimately confusing. To disentangle the potential confusions, particularly, the ramifications of irrationality and dishonesty, here we resort to evolutionary game theory. Specifically, we formulate and analyze the masking problem with a fictitious pair of young lovers, Alice and Bob, as a Sir Philip Sydney (SPS) evolutionary game, inspired by the handicap principle in evolutionary biology and cryptography figures in computer science. With the proposed ABD (Alice and Bobs dating dilemma) as an asymmetric four-by-four strategic-form game, 16 strategic interactions were identified, and six of which may reach equilibriums with different characteristics such as separating, pooling, and polymorphic hybrid, being Nash, evolutionarily stable or neutrally stable. The six equilibrium types seem to mirror the diverse behaviors of mask believers, skeptics, converted, universal masking, voluntarily masking, coexisted and/or divided world of believers and skeptics. We suggest that the apparently simple ABD game is sufficiently general not only for studying masking policies for populations (via replicator dynamics), but also for investigating other complex decision-making problems with COVID-19 pandemic including lockdown vs. reopening, herd immunity vs. quarantines, and aggressive tracing vs. privacy protection.