Adaptive calibration in a world of human universals

A common complaint leveled historically at evolutionary approaches to human behavior is that they focus too much on human universals and not enough on human variation. However, over the last decade or so there has been greater recognition that this is an oversimplification of the adaptationist approach. The basis was in understanding human nature or what are referred to as human universals (Brown, 1991), such as sexual jealousy or incest avoidance. Such understanding provides solutions to human wide problems. Infidelity is a threat to high investment mating relationships. Over human history, males have faced the recurrent problem of paternity uncertainty and the specificity of male sexual jealousy can be viewed as an adaptive response designed to motivate behavior that will reduce the reproductive cost of sexual infidelity to men (Buss, 2018). Similarly, humans, as members of a social species, spend significant time with genetic relatives, including opposite sex relatives. However, selecting close kin as sexual partners is disadvantageous due to the risk of negatively impacting recessive mutations. While in some species, offspring disperse to avoid inbreeding, humans have done this much less frequently over our history. Thus, avoiding incest is an adaptive problem to solve, and indeed adaptations exist in the form of information processing systems that weigh cues of relatedness in order to avoid incest and its resulting costs (Lieberman & Patrick, 2023).However, in addition to understanding human universals, there has also always been interest in understanding what shapes behavioral variation within and between individuals. Understanding what makes us human does not preclude understanding the variable ways in which our human nature is expressed. For example, not everyone experiences or expresses sexual jealousy the same way. Some individuals are more sensitive to cues of the likelihood of infidelity and this sensitivity can be influenced by within-couple mate value discrepancy, past history of experiencing infidelity, as well as other environmental factors such as the local sex ratio (Buss, 2018).A number of scholars have argued for the integration of evolutionary psychology and the field of individual differences (Buss, 2009;Kanazawa, 2011;Maestripieri & Boutwell, 2022). Heritable individual differences can be adaptive and functional. But in addition, differences in behavior can be contingent on current and past environmental calibration of universal psychological and physiological mechanisms (Del Giudice et al., 2011;Ellis & Del Giudice, 2019;Schwartz et al., 2023). Adaptationist approaches now and in the future should continue to examine the ways in which the universal architecture of human nature is calibrated to variable environmental conditions across the lifespan (Sell et al.,2017).Two examples of areas of research that have benefitted from evolutionary approaches that emphasize the role of the environment in calibrating psychological mechanisms are evolutionary developmental psychology's (evo-devo) approach to variation in parental investment and work on variations in female mate preferences.According to Trivers (1972), parental investment includes any parental effort that increases an offspring's chance of surviving and reproducing while reducing the parent's ability to invest in other current or future offspring. The adaptive problem associated with parental investment is how to allocate limited, zero-sum resources (time, energy, etc.) among current offspring and potential future offspring and maximize one's inclusive fitness. As with solutions to other universal human problems, evolutionary psychologists posit that adaptive allocation decisions are made automatically and on an unconscious level via universal neuroendocrine and psychological mechanisms designed by natural selection to attend to certain environmental cues and produce contingent responses based on those cues (Bugental, 2000;Daly & Wilson, 1980). The specific allocation of parental resources involves trade-offs as well as developmental consequences for both the offspring and the parent. As such, evolutionary psychologists have long been interested in identifying factors that influence individual differences in these parental investment decisions. What factors determine whether a parent invests less in more offspring or invests more in fewer offspring? Under what circumstances will parents invest heavily in current offspring, potentially risking their own survival and/or future reproductive opportunities, versus conserve their resources for future offspring? What environmental cues influence how parents distribute their limited resources among multiple offspring (e.g., even or biased)? Daly and Wilson's (1984) investigation of infanticide cases provided some of the earliest evidence that parental investment decisions are influenced by the quality of the offspring (i.e., their reproductive potential), parental resource availability, and maternal age. Specifically, their investigation revealed that children with low reproductive potential, born to parents of low socioeconomic status, and/or born to younger mothers were at greater risk of neglect, maltreatment, and infanticide. Later work by Beaulieu and Bugental (2008) found evidence that, in addition to the previously observed main effects of offspring reproductive potential and parental resource availability, there was also an interaction between those two factors. When resources were high, mothers invested more in their low reproductive value infants (relative to their high reproductive children); and when resources were scarce, mothers invested less in their low reproductive value infants (relative to their high reproductive children). In more recent work, researchers proposed evo-devo models of how environmental factors generate variable adaptive responses leading to differences in parental behaviors (including parental investment) and their effects on child dev