Costly signaling theory in evolutionary psychology refers to uses of costly signaling theory and adaptationism in explanations for psychological traits and states. Often informed by the closely related fields of human behavioral ecology and cultural evolution, such explanations are predominantly focused on humans and emphasize the benefits of altering the perceptions of others. They also stress the need to do so in ways that are difficult to fake, due to the widespread existence of adaptations which demand reliable information to avoid manipulation through dishonest signals.
Although initially created to explain costly morphological traits as honest signals of an individual's underlying quality resulting from sexual selection, the scope of costly signaling theory has been expanded to include signals of cooperative intent and need, with the targets of such signals often going beyond potential mates.
Costly signaling background
Almost any organism can benefit from altering the perceptions, behavior, and physiology of others in its environment in ways that favor itself. Particularly true in social species, the result is often investment in signals to enhance one's perceived attractiveness, formidability, or cooperative value to members of their own species.
A signal differs from a cue in that signals evolved to influence the behavior or perceptions of others, while a cue is any piece of information an organism uses to alter its current state that was not created for this purpose. As signals evolve due to their communicative effects and are often not fully linked to the qualities being signaled, they have the potential to be easily faked by those who do not possess a trait. Such faking would likely be favored through natural selection due to the ubiquity of conflicts of interests among living things. These conflicts create situations in which the negative impacts on others are either not relevant, or still worth the benefits to the signaler.
Although there are substantial risks of being deceived, targets of a signal may still benefit from paying attention to this information as long as it is honest and relevant to fitness-related problems. For this reason, natural selection is thought to have resulted in adaptations in many species to verify the validity of signals before accepting the information as reliable. Signaling in a costly manner is thought to satisfy these anti-manipulation adaptations when the resultant signals are comparatively cheaper to produce for those who have the underlying quality compared to those who lack it. In these instances, individuals with the quality can maximize their fitness by investing more in the signal relative to those who lack the quality or possess it to a lesser degree, thereby resulting in a signal that, while often not impossible to fake, tends to not be worth faking.
Costly signals of beneficial qualities The majority of costly signaling explanations involve behaviors that broadcast beneficial traits about oneself to others. In many instances, these signals are expected to be directed towards potential mates, with males often thought to benefit more from such signaling due to their relatively low levels of investment in offspring leading to greater fitness benefits in having multiple partners. However, the importance of cooperation over human evolutionary history is also thought to have resulted in many signals that involve showing one's potential as a cooperative partner to those outside of mates.
Costly signals of embodied capital
Hunting Primarily through the work of human behavioral ecologists, hunting among humans has received much attention as potentially serving as an honest indicator of various qualities due to its potential for differential costs. The first signaling approaches to hunting emphasized that although hunting can provide an important source of calories and nutrients in small-scale societies, it is still practiced when it is less efficient than other means of food production and often involves the targeting of species that result in less meat for a given period. In response to this and findings that food is typically shared widely in small-scale societies, the show-off hypothesis suggests that men may hunt difficult prey in part due to reputational benefits that increase the likelihood that others will want good hunters in their group because of the benefits they provide.
Later models built off this by incorporating costly signaling theory. In addition to the costs of inefficiency reported in some hunts, hunting can be costly in terms of the time needed to develop one's skill, the risks involved, and the resources required for a successful hunt. For this reason, it has been proposed to honestly signal a wide range of traits including strength, skill, ability to buffer risk, leadership, and various beneficial cognitive traits, all of which can increase one's attractiveness to mates and cooperative partners. As with other costly signals, this is due to hunting being relatively more costly for those who lack the previously mentioned qualities or possess them to a lesser degree, with such individuals being more likely to produce less effective signals and become injured, both of which deter faking the signal.
Although not mutually exclusive with the show-off hypothesis, such approaches have been presented as explaining a wider range of hunting behaviors as the benefits that come with signaling one's qualities does not require that hunting benefits others, thereby better accounting for relatively wasteful displays. However, these models still emphasize the benefits of providing for others as meat sharing is often public and attracts large audiences, thereby increasing the effectiveness of a signal to increase one's status within a group.
Evidence in favor of hunting being a costly signal of beneficial qualities has primarily come from its valuation by group members and by the benefits good hunters enjoy. In small-scale societies, individuals can often tell a good hunter from a bad one, with skilled hunters having been reported as having higher status than those less skilled. Material benefits are also seen with good hunters having been shown to have increased reproductive success, more political power, and more support for one's kin in both times of illness and health.
Compared to the existence of the reputational benefits of hunting, its importance in explaining human hunting relative to explanations involving kin selection or reciprocity is more controversial. This is primarily seen through disagreement on the amount of provisioning that happens within a family and the general ability of hunters to control who receives the meat they bring in.
Risk-taking Often invoked in costly signaling approaches to hunting, risk-taking has been suggested to result in honest signals of quality in other forms. As risk increases, so do the costs that come with failure. This results in greater costs for those who do not have qualities which allow for greater chances of success or the ability to buffer failure relative to those who possess such qualities. For this reason, risky behaviors may often be honest signals, with individuals who lack the relevant traits being expected to avoid risk or suffer too much damage from failures to maintain risky behavior.
Many beneficial qualities have been suggested to underlie risk-taking behavior. For example, physical skill, good judgment, or bravery have all been argued to increase the chances of success in risky situations. Similarly, social dominance, confidence, and ambition may also help in competition among conspecifics, with social dominance, ambition, and wealth also potentially limiting the costs of failure.
In general, the targets of risky signals are often thought to be potential mates. This is primarily due to the finding that young males (who are the age and sex class with the highest reproductive variance) take more risks than any other group in both experiments and observational data. By undertaking risky endeavors, males are thought to signal the previously mentioned qualities which may be directly related to one's ability to provision and protect one's family. However, traits like bravery and physical prowess may also be valued by cooperative partners due to their benefits in group-hunting and warfare, thereby increasing the potential audience for risk takers.
Physical attractiveness Physically attractive traits have also been hypothesized to be signals of mate quality, with facial characteristics, body type, voice characteristics, and body modification having all been suggested to provide information relevant to reproduction. However, most approaches focus on how the information is relevant to the receiver rather than whether the information takes the form of signals or cues, with the two possibilities often hard to distinguish between.
Although exceptions exist, costly signaling theory has mainly been incorporated into explanations for attractive male traits in a wide range of species. In humans, both low voice pitch and facial masculinity in males have been suggested to be honest indicators of male quality due to testosterone's connection to facial and vocal cord development and its hypothesized role in mediating tradeoffs. From such perspectives, only high-quality males can afford to invest heavily in phenotypic qualities outside those needed for survival due to lower relative costs of such investment, with testosterone's linking of these traits with facial and vocal characteristics preventing individuals from faking these signals. Additionally, low voice pitch may also be difficult to fake in the short-term due to activation of the autonomic nervous system, which controls fight-or-flight responses, altering voice pitch. For this reason, only individuals who are confident in their ability are likely ability can afford to maintain low levels of arousal, thereby potentially serving as an honest signal of formidability.
Regardless of whether the information comes from cues or signals, differences are expected in which information is valued by each sex. In general females are expected to be more sensitive to information about the ability of potential mates to acquire and defend resources, while males are expected to focus more on potential partners' ability to conceive and take care of future children. Outside of these areas, both sexes are often suggested to benefit similarly in signaling pathogen resistance or a lack of harmful mutations due to their hypothesized importance over human evolutionary history.
Art Art has also received attention as a costly signal of beneficial qualities relevant to sexual selection.Miller, G. F. (2016). Art-making evolved mostly to attract mates. In On the origins of art [exhibition catalog] pp. 163-213. Hobart, Tasmania: Museum of Old and New Art. If defined as environmental modification lacking adaptive functions outside of sexual selection, art or art-like behavior has been observed in spiders, crabs, fish, and birds in addition to humans. Unlike the art of other species, however, the form of human art is generally not considered to be genetically encoded. Instead, adaptationist approaches often involve the hypothesis that humans possess adaptations capable of resulting in a wide range of artwork as sexual signals and adaptations for correctly evaluating the information being signaled.