Over time species can evolve new traits and behaviors that increase reproductive success

Pubertal timing

Evolutionary theory highlights the adaptive value of within-species variability. Optimal biological and behavioral strategies differ depending on the nature of the environmental context as well as the characteristics of the organism such as age, sex, health, or physical size. Pubertal timing is an example of an aspect of human physiological development that shows phenotypic plasticity. As suggested above, the typical sequence of reproductive development in humans includes a period of delay between puberty and sexual debut. During this time, adolescents acquire the physical, social, and economic resources necessary to attract a mate, reproduce, and successfully rear their young to reproductive age.

From an evolutionary perspective, early puberty is understood as an adaptive strategy in the context of family stressors and a negative quality of family relationships (Belsky, Steinberg, & Draper, 1991; James, Ellis, Schlomer, & Garber, 2012). Over the course of human evolution, early exposure to harsh, unpredictable family contexts, and/or inadequate resources has been shown to accelerate the life history resulting in an earlier onset of pubertal physical maturation and earlier age of sexual debut (Ellis, 2004). This relationship is particularly notable for girls. Physiological response to stressful conditions, especially the frequent activation of the HPA axis, is associated with early pubertal development (Ellis & Del Giudice, 2014). According to evolutionary theory, early onset of puberty and accelerated entry into sexual activity can be viewed as adaptive when parental investment is low and resources are inadequate or uncertain. Those individuals whose sexual development is accelerated increase their chances of attracting a mate and surviving to reproduce.

However, these adaptive advantages also come with costs. In contrast to those who delay reproduction into later adolescence and adulthood, early entry into sexual reproduction is associated with increased risks of premature birth and low birth weight in the offspring, as well as health and mental health problems for mothers. The phenotypic plasticity associated with pubertal timing consists of trade-offs. Accelerated life history provides a longer reproductive period with more possible offspring, but increased risks of infant morbidity and mortality and fewer resources to support parenting. Slower life history results in a shorter reproductive period with fewer offspring, but greater likelihood of health and survival of offspring as well as more resources to support parenting (Hawley, 2011). Taking a population perspective, the fertility rate estimate for population replacement is 2.1 live births per adult woman. Currently, across the 28 countries in the European Union, the average fertility rate is 1.58, well below population replacement (Eurostat, 2018). Taken from an evolutionary perspective, one might infer that the short-term adaptive advantages to the individual for the slower life history may not be so advantageous for the long-term survival of the larger group.

Evolutionary theory predicts that individuals will avoid mating with close kin and will cooperate preferentially with relatives. Theory also predicts that mechanisms facilitating assessment of kinship will evolve. The kin-recognition process comprises three components: the production of kin labels that correlate reliably with relatedness, the perception of these labels in others and a comparison to a recognition template, and the action taken, if any, as a function of estimated relatedness. Each of these components is discussed as they relate to ecological and life-history parameters of animals, including an example of the mechanisms and functions of recognition in a model organism.

Evolutionary theory has inspired a number of writers to comment on its ethical implications. These writings constitute a subject entitled ‘evolutionary ethics’. Starting with Charles Darwin and Herbert Spencer, attempts have been made to explain or to justify ethics from an evolutionary perspective. The history of these attempts is broken down into three periods: first, starting with Darwin and Spencer; second, with the investigations of scientists such as Julian Huxley associated with the formulation of the modern theory of evolution in the first half of the twentieth century; and then third, with the ideas inspired by E. O. Wilson and sociobiology.

Evolutionary theories

Evolutionary theories take the long-term look at the emergence of the human species. According to this perspective, humans of today carry with them genetically guided characteristics passed from generation to generation that have contributed to survival and reproductive success. This chapter introduces the place of adolescence within Darwin’s idea of fitness, the link between human adolescence and adolescence in other primates, and the concept of adaptation to an ecological niche. The chapter incorporates concepts from evolutionary psychology to consider the integration of genetic and social forces that result in phenotypes related to puberty, fidelity to a group, sex-specific sexual strategies, aggressiveness and bullying, and the adaptive nature of risky behaviors.

Conditions for Evolutionary Theories of Aging

Evolutionary theories of aging are based on particular assumptions initially articulated by Williams (1957). These were extended and clarified by Hamilton (1966), Charlesworth (1993), and Abrams (1993) and recently reviewed by Gaillard and Lemaître (2017). It must be stressed that evolutionary theories of aging were originally defined for those systems that satisfied those assumptions.

There is a clear distinction between the soma and germ line. The germ line is the only source of genetic variants transmitted to the next generation. While the soma is required for reproduction, somatic mutations perish with individual death. As discussed below, this condition is relaxed in many plants and problematic in many unicellular organisms.

Natural selection acts on competing alleles. This is a cornerstone of current evolutionary thinking and does not exclude any taxa.

At least some alleles have pleiotropic effects. This condition is also firmly supported by our current understanding of evolution and development.

Reproductive value decreases with individual age. This is based on the logic that death is inevitable, regardless of aging. There is some debate regarding its generalization (Vaupel et al., 2004); however, this is beyond the scope of this article and I recommend (Shefferson et al., 2017) for a more detailed discussion.

Populations are age-structured. This requires distinction between parent(s) and offspring. Note that cell division (budding, fission) in unicellular organisms can be asymmetric, with one cell determined as the offspring.

It is very important to note that these assumptions leave ample scope for the existence of non-aging cells and organisms and their occurrence does not invalidate evolutionary theories of aging. At the same time, it is clear that current evolutionary theories of aging cannot explain all variation in the perpetuity of particular lineages, their longevity, aging, death and extinction. As an example, germ lines, by definition, represent non-aging cell lineages inside aging bodies. I will return to lineages that deviate from these assumptions in “Situations Beyond the Evolutionary Theories of Aging” section 6.

Evolutionary theory views violence in the context of its likely costs and benefits measured in the currency of the actor’s inclusive fitness. Violence is one potential means of resolving conflicts over scarce resources for survival and reproduction. Many species have evolved heritable specialized traits that are useful in violent encounters, such as antlers and large canines, as well as neural mechanisms controlling the use of force. As violence tends to elicit counterviolence, social disapproval, or other costs, it is unlikely to pay if used indiscriminately. The realization that selection operates on the combined or ‘inclusive’ fitness of an individual and its relatives has inspired new hypotheses and findings of the patterns of conflict and violence. Many patterns of violence turn out to be consistent with the assumption that humans evolved to be effective competitors and kin benefactors.

Comparative Predictions of the Evolutionary Theory of Aging

The evolutionary theory of aging is unusual among theories of biology in that it makes some absolute predictions. The experimental corroborations of the prediction that the pattern of aging should evolutionarily respond to manipulation of the force of natural selection have already been mentioned. With even greater strength, the evolutionary theory of aging predicts that all species that exhibit a well-defined separation of germline from soma must age. Conversely, the evolutionary theory predicts that all species with strictly symmetrical fissile (splitting in two) reproduction must be free of aging. (This does not imply absolute immortality, since such organisms could still die from disease, predation, or mechanical injury.) These two predictions can be tested extensively using comparative data.

However, many species exhibit neither a well-defined soma nor fissile reproduction. Colonial coelenterates, such as corals, or grasses may have fairly ambiguous delineation of ‘organisms.’ Still other forms may combine fissile with sexual reproduction. In these cases, the evolutionary theory does not provide any simple prediction about the pattern of aging. Fully developed population genetics theory could, of course, be formulated to address any of these ‘hybrid’ cases, and some progress along these lines has been made by M. E. Orive. There is no fundamental violation of theory, only some difficult special cases.

Evolution of Aesthetics

Evolutionary theory has been applied to specific aspects of the creative process, including aesthetics (Berlyne 1971; Lowis 2004; Martindale 1990Berlyne, 1971Lowis, 2004Martindale, 1990). Martindale, for example, gleaned from various historical and experimental analyses that supported a “psychological theory of aesthetic evolution.” Martindale’s premise is that artistic change is predictable. (For this reason the title of his book is The Clockwork Muse.) It is predictable because there is a canon that governs all art. Somewhat ironically, that canon is, “rules must be broken … laws must be disobeyed” (p. 11). The relevant law reflects the universal need for novelty. This is expressed in different ways at different times. Sometimes it leads to outrageous styles, sometimes to the fairly mundane or sedate. Behind it all is the need for novelty, which is in turn a reflection of the need for arousal.

1.1 Evolutionary and Social Psychological Perspectives: Towards a Synthesis

Evolutionary theories enable understanding of the ultimate significance of heterosexual relationships, specifically the determinants of partner selection, whereas social psychological perspectives provide insight into the more proximate factors involved.

The evolutionary models of partner selection essentially view individuals as acting on the basis of evolved mechanisms, selected with a focus on maximizing ancestors' genetic fitness or increasing the likelihood of raising healthy offspring (Kenrick et al. 1993). These models contend that gender differences in preferences or selection criteria are cross-culturally universal, and have unfolded through sexual selection pressures over millions of years. As the physical condition of females is necessary for offspring survival, males generally tend to focus upon characteristics indicative of this aspect. On the other hand, females place more value on males' ability to contribute to resources.

A prominent theoretical model in social psychological perspectives on partner selection is the social exchange model, which posits that individuals search for partners who have resource value that is equitable with one's own ‘market value.’ In other words, there is an exchange of valued traits or resources (Kenrick et al. 1993). Based upon the market value of each trait, which varies cross-culturally, both women and men seek partners who will maximize gains and minimize costs. Social psychological models generally explain gender differences in terms of structural powerlessness of women and traditional sex role socialization patterns. Evolutionary theories, on the other hand, emphasize gender differences in terms of the reproductive investment hypothesis (Buss and Barnes 1986).

Evidence of the universality of certain gender differences in partner selection preferences across cultures supports the role that evolutionary forces play in shaping cultural factors that mediate the gender-based criteria for partner selection (Buss et al. 1990). Nevertheless, predictions related to psychological mechanisms in selection preferences offered by evolutionary models need to be viewed in conjunction with specific cultural-environmental contexts (see Evolutionary Social Psychology).

The sexual strategies theory proposes an integrated contextual-evolutionary perspective of partner selection. Based on the premise that human mating is inherently goal-directed, the theory incorporates factors from the larger context that have a bearing on partner selection and states that mating strategies are context-dependent in terms of the social milieu and the duration of the relationship. Also, the principles that govern selection by women and men are different and, to that extent, the psychological strategies or mechanisms adopted to maximize reproductive success and offspring survival also differ (Buss and Schmitt 1993).

Abstract

Evolutionary theory is the organizing framework for the life sciences because of its unique value in deriving falsifiable predictions about the causal structure of organisms. This chapter outlines the relationships of evolutionary principles to the study of phenotypic variation and defines two distinct paradigms for personality science. The first of these, dimensional cost-benefit analysis (DCBA), entails analyzing the reproductive cost-benefit tradeoffs along inductively derived personality dimensions (e.g., the Big Five) to derive predictions regarding adaptively patterned variation in manifest trait levels. The second paradigm, ground-up adaptationism (GUA), requires building models of specific psychological mechanisms, from the ground-up, including their variable parameters that result in manifest behavioral variation. After evaluating the strengths and limitations of these paradigms, it is concluded that (1) inductively derived dimensions of person description should not serve as the field's explanatory targets; (2) GUA represents the most powerful available framework for elucidating the psychological mechanisms, which comprise human nature and produce its diverse range of behavioral variants; and (3) the goals of adaptationist evolutionary psychology are the same as those guiding personality psychology's next era: to identify the mechanisms that comprise the mind, figure out how they work, and determine how they generate behavioral variation.