Life History Evolution: An Explanatory Framework
Abstract The purpose of this chapter is to supply the reader with foundational information about life history theory without which the remainder of the book would not make sense. Herein, it is explained that life history was originally an exclusively biological theory relevant to the timing of gestation, development, maturation, and death. Later, it was used to explain variation among human populations not only on these core biological variables, but also on psychological and social variables. Psychological variables include personality traits like conscientiousness, mating strategy, and intelligence, while sociological variables include altruistic effort, cultural capital, and communal affiliation. With this primer on life history evolution, the reader can better assimilate specific life history knowledge detailed in subsequent sections.
Keywords Somatic effort • reproductive effort • r-selected • K-selected • pace of life
Mark the difference in maturation, fecundity, and longevity between annual and perennial plants (Barrett et al. 1997), bats and terrestrial rodents (van Schaik and Isler 2012; Wilkinson and South 2002), and small and large undulates (Harvey et al. 1989), and questions will arise only answerable within a life history evolutionary framework (Hertler 2016). Life history is a mid-level evolutionary biological subdiscipline (Figueredo et al. 2005) that explains values across seven intercorrelated variables: (1) size at birth;
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S.C. Hertler, Life History Evolution and Sociology, DOI 10.1007/978-3-319-48784-7_3
(2) growth pattern; (3) age and size at maturity; (4) number, size, and sex ratio of offspring; (5) age- and size-specific reproductive investments; (6) age- and size-specific mortality schedules; (7) length of life (Stearns 1992; Braendle et al. 2011; Hertler 2016). Variation across these life history traits creates a continuum that is variously labeled fast and slow, or r and K,1 which, in aggregate, measures an organism’s pace of life; that is, the pace at which an organism lives out its life cycle (Reale et al. 2010; Johnson et al. 2012; Niemela et al. 2013). As a group, insects are fast or r strategists in that they are small at birth, grow rapidly, mature while still young and small, have relatively more small offspring to which they provide scant parental investment, senesce rapidly, and die early (Geary 2003). Alternatively, elephants are slow or K strategists in that they are large at birth, grow slowly, become mature and fertile only after many years of delay, have few and large offspring to which they provide consistent parental investment, senesce slowly, and die late (Stearns 1983). Life history evolution measures the balance of bioenergetics resources (Figueredo et al. 2013) allocated toward maintaining the organism, defined as somatic effort, or replacing the organism, defined as reproductive effort (Williams 1966; Hewlett et al. 2000; Figueredo et al. 2005). This is consistent with the Disposable Soma Hypothesis,2 which properly identifies the organism as a temporary vessel in which genes reside for a time (Kirkwood and Holliday 1979; Kirkwood and Austad 2000). Following this, the more disposable the soma, the more r selected the species. Fast life history strategists invest little in bodily growth and maintenance, funneling resources instead to reproducing themselves early and amply (Kaplan and Gangestad 2005). Alternatively, the slow life history strategist, in effect, holds onto the genetic, intergenerational baton longer, and thereafter passes it on to only a few long-developing, high- quality offspring (Hertler 2016).
As reviewed previously (Hertler 2016), all species fall at some point along the life history continuum; but there are species-specific life history parameters, as opposed to fixed values (Figueredo et al. 2005). Humans, taken as a species, are highly K selected (MacDonald 1997; Ellis 1987, 1988), but some are more so than others (Figueredo et al. 2005). This human life history variation was first described by Rushton (1985) in a paper entitled Differential K Theory: The Sociobiology ofIndividual and Group Differences. In the 30 years since the initial articulation of Rushton’s Differential K Theory, a host of research and theoretical developments have documented the physiological, behavioral, social, and cultural ways in which human life history variation is expressed
(Weizmann et al. 1990; Chisholm 1999; Figueredo et al. 2005; Gladden et al. 2008; Walker and Hamilton 2008; Griskevicius et al. 2011; Sherman et al. 2013; Wenner et al. 2013). All such variation will be familiar to the readers of Coming Apart.
- 1. As previously described (Herder 2016), “the r used above refers to rate, which, along with K for carrying capacity, was part of the shorthand notations used by the innovators of life history theory, MacArthur and Wilson. Though the density dependence that these notations were used to calculate has been superseded by direct measures of mortality, their use above follows the modern convention of using r and K as shorthand references to fast and slow life histories respectively.”
- 2. Disposable Soma Theory Encapsulated
The concept of a disposable soma can be disconcerting, given that the organism, whether animal or person, author or reader, is simply a temporary vehicle for the propagation of genetic material. Such a view undermines the view of self, especially as it has been exalted since the Renaissance, as an ultimate end. Putting aside the many existential and philosophical implications of somas being disposable, it is important to provide some further explanation of this important concept. Such a theory would hardly be conceivable without the work of Richard Dawkins and W. D. Hamilton. Dawkins achieved a conceptual revolution in Darwinian evolution by discussing the gene, instead of the organism, as the level of selection. This more precisely emphasized that the evolutionary process is simply a change in gene frequencies. Hamilton showed the soma to be disposable through a similar emphasis on genes by developing his theory of inclusive fitness, otherwise known as kin selection. By either name, this process recognizes relatives as repositories of shared genes. The higher the level of genomic overlap, the more the interests of self and other overlap. It is in this way that self-sacrifice is more likely for a daughter than a niece; for a niece than a cousin; for a cousin than a stranger. Genetic propagation, not individual survival, is paramount; a process that is illustrated by the male Australian Redback Spider which increases offspring viability or number by becoming a nuptial meal for his mating partner.