Vigil is to be applauded for tackling such a large and complex topic as the differences in emotivity between the sexes and for attempting to produce a model that reconciles psychological and evolutionary approaches. Vigil's summary of these differences (target article, sect. 3.2) is written crisply and directly, and will be a useful reference for anyone working in this area. With some adjustments and additions, his model or a derivative of it might successfully merge evolutionary and psychological approaches.

The model assumes that “approach” and “avoid” are the only possible responses to external stimuli. However, animals often respond to stimuli by taking a “wait and see” strategy to obtain more information. Second, to use Vigil's examples, food may be laden with toxins, and mates may sometimes become predators, so organisms seldom face a dichotomous choice, but rather must monitor many requirements and make the appropriate trade-offs. Third, even when it might be ultimately desirable to avoid a stimulus – for instance, a predator – there might be several viable short-term responses. The potential prey might freeze to avoid detection. If it is already being stalked, it might simply inform the predator that it has been seen so the latter can no longer mount a surprise attack. If the predator does attack, the best response might be to stand and fight. It is even more complex when, instead of responding to predators, animals must respond to highly social conspecifics with common and conflicting interests. Hence, the model would be stronger if it recognized that most responses to social stimuli probably fall within a large grey area between “avoid” and “approach.”

Vigil then applies the model to sex-related differences in emotivity, using for support the concepts of intrasexual competition (Darwin Reference Darwin1871) and reciprocal altruism (Trivers Reference Trivers1971). The model would be stronger if it also considered related concepts, such as intersexual selection (Darwin Reference Darwin1871) and the ensuing sexual conflict (Trivers Reference Trivers and Campbell1972). Vigil points out that most social interactions are with members of our own sex, and women have more intimate relationships and with fewer individuals than men do, and he attributes these patterns to sex-related differences in philopatry. It might be worth also considering that variance in reproductive success is higher for males than for females, so competition among males is stronger than among women, not just different in its style and in its setting. Second, one must also wonder why displaying emotions might be more useful in more intimate situations. The opposite could be argued. Powerful leaders throughout history, who happen to have been mostly male, demonstrate that displaying emotions can be a powerful means of controlling and motivating the masses. Third, as a sexually reproducing species, there is only one way for our genes to make it to the next generation – by interacting with the opposite sex. Maybe the model could incorporate intersexual selection (a.k.a. epigamic selection or mate choice) instead of focusing solely on intrasexual competition. Finally, sexual relationships are a constant struggle between common and conflicting interests. Within every sexual relationship, there is the potential for cooperation but also for deceit, manipulation, and exploitation. An enormous body of work over the past 40 years has been based on that premise (Andersson Reference Andersson1994; Arnqvist & Rowe Reference Arnqvist and Rowe2005; Low Reference Low2001; Majerus Reference Majerus2003; Trivers Reference Trivers and Campbell1972). It is peculiar that a treatise on the differences in emotivity between the sexes would not consider the one emotion that for millennia has provided a livelihood for thespians, singers, poets, and playwrights; humanity's greatest and most wonderfully labile and complex emotion and obsession: romantic love.

When mating, men have been selected to be relatively more concerned with quantity and women with quality (Betzig Reference Betzig1986; Reference Betzig and Ellis1993; Buss Reference Buss2003; Helle et al. Reference Helle, Lummaa and Jokela2008; Murstein Reference Murstein1986). Men compete for resources mostly with other men, but they also compete for the attention of women by displaying, emphasizing, and exaggerating their strength, status, and wealth. In contrast, women compete for high-quality males by displaying, emphasizing, and exaggerating their potential fecundity, beauty, and/or youth, all of which are highly positively correlated. Emotional displays are signals, and as such, their purpose is to persuade, cajole, and manipulate the intended receivers (Maynard-Smith & Harper Reference Maynard-Smith and Harper2003; Searcy & Nowicki Reference Searcy and Nowicki2005). There is nothing more potentially deceptive than a simple smile. A new hypothesis suggests itself: emotivity, or lack thereof, might be yet another way to attract the opposite sex. Given that children are more emotive than adults, men might conceal their emotions as a way to display their strength and maturity. In contrast, women might express more and more variable emotions in order to display their youth. In any case, consideration of intersexual selection offers a different and more complete perspective.

Vigil's social framework of emotions consists of a two-dimensional construct with “trustworthiness” on one axis and “capacity”, or, perhaps more aptly, “ability”, on the other axis. This conceptualization is similar to Leary's (1957) model, which had “love” and “dominance” as the two axes. Just like Leary's model, Vigil's is reasonable, interesting, and compelling, and it could have been derived without any knowledge of evolutionary biology. In applying the model to sex-related differences in emotions, evolutionary concepts are used only for support, not for illumination. Unfortunately, integration must encompass all evolutionary biology, not just selected concepts that agree with the model. If anything, the model highlights the fact that some areas of psychology and evolutionary biology, despite over 50 years of progress and a mutually acknowledged desire for integration, might be getting closer but are still entrenched in their own ways of thinking.

Following Darwin's (1872) pragmatism, Vigil addresses the expression of emotions, not emotions per se, as the latter are more difficult to observe, quantify, and classify (e.g., Nesse & Ellsworth Reference Nesse and Ellsworth2009), and anyway, can only affect fitness when they alter behaviour. This important distinction might help us merge evolutionary and psychological approaches by allowing us to abandon arbitrary conceptualizations of what is inside a mind – the sensation of emotions – and instead lead us to focus on their ecology and functions. It is ironic that, evolutionarily, it only matters what emotions do, not how they feel.