Addressing our inner salmon in an evolutionary framework for psychopathology

Life history theory is an elegant instrument for describing major differences in patterns of life history traits across plant and animal taxa (Charnov, 1993; Roff, 1992, 2002; Stearns, 1992). Typical life history traits discussed in the classic evolutionary biology literature include size at birth, growth pattern, age of sexual maturation, size at maturity, age of first reproduction, number and sex ratio of offspring produced, age and size-specific reproductive investments, age and size-specific mortality schedules, and length of lifespan (see Stearns, 1992). A basic assumption of the classic optimality approach to life history theory is that, given adequate genetic variation, the evolution of species has involved natural selection of optimal combinations of these traits. However, genetic and other constraints, and trade-offs have reduced the set of possible combinations. Life history theory predicts trade-offs between energetic investment in growth, maintenance, and reproduction across species, of which a trade-off between the main constituents of reproductive investment, mating and parental effort, may be the most common (McGlothlin, Jawor, & Ketterson, 2007). It is easy to see how if organisms possess finite resources that trade-offs affecting life history traits would necessarily evolve over evolutionary time. If the “pie of finite resources” is divided up between life history traits, taking a large slice of one type of trait leaves less of the pie to be divided into other forms of investment. Among vertebrate species, for example, salmon have very different life histories than primate species. Their life history consists of relatively rapid growth, early maturation and first reproduction, small size, little parental care, and the production of a high number of offspring, followed immediately by death in semelparous species,eclipsing a postreproductive period. In contrast, the life history of human beings consists of relatively slow development, late puberty and first reproduction, iteroparity, large body size, low number of offspring, followed by high parental investment (extended to grandparental investment) and a long life span, including a female postreproductive period