SD–IE and other differentiation effects in Italy and Spain

Highlights

• We test SD–IE, CD–IE, and SLODR among Spanish and Italian provinces.

• Both countries show increasing differentiation effects with high K and high g.

• SD–IE tends to be a Jensen effect and cognitive differentiation an anti-Jensen effect.

Abstract

SD–IE is a strategic differentiation effect present amongst indices of life history (LH), such that persons and populations of slow LH are more differentiated compared to those of fast LH. We found that this phenomenon is present amongst provinces in Italy and Spain, similarly to demonstrations among US states and Japanese prefectures. The average effect size of SD–IE was found to be bigger in Spain and Italy. We also tested cognitive differentiation as a function of life history speed and IQ (high-K and high-IQ provinces having higher cognitive differentiation), and found that these effects are also present in the Italian and Spanish regions. Most cognitive differentiation effects were statistically significant in spite of the small number of provinces, but all trended in the predicted direction. We discuss the findings from a bio-historical perspective, taking into account the ethnic variability present in Spain and Italy.

Introduction

Life history strategies constitute coordinated sets of bioenergetic resource trade-offs between mating effort, parenting, health, defense of one’s community, and so on (Ellis et al., 2009, Hairston et al., 1970, MacArthur and Wilson, 1967; Pianka, 1970). Organisms that focus on mating effort instead of other domains are said to have ‘fast’ life histories; those that focus on domains such as parenting and somatic maintenance have ‘slow’ life histories. Within human populations, individual differences in personality are genetically related to health and a general behavioral life history factor termed K (Figueredo and Rushton, 2009, Figueredo et al., 2004). The superordinate of these dimensions is a global life history super-factor termed super-K (Figueredo, Vásquez, Brumbach, & Schneider, 2007). Not everything that relates to life history at one level of aggregation necessarily relates to it at different levels of aggregation, however. The g factor, for example, seems to correlate with life history traits between populations (Boutwell et al., 2013, Meisenberg and Woodley, 2013, Rushton, 2000, Templer, 2008), but very little with individual differences in life history (Woodley, 2011). This disparity has been termed “Rushton’s Paradox” (Meisenberg & Woodley, 2013).

One possible solution to Rushton’s Paradox is that high-K people, although not possessing higher g overall, nonetheless exhibit more specialized cognitive abilities (Woodley, 2011). As high-K populations generally live in environments where population density, stability and competition are high, specialization may be a fitness-enhancing strategy. Specialization leads to enhanced aggregate efficiency (because there are specialists for every niche) and a higher carrying capacity. Therefore, it is a logical component of a high-K strategy. Conversely, cognitive generalism may be the strategy of choice amongst low-K (fast) life history populations, as these populations live in unstable environments where there is a need to switch between niches. This cognitive differentiation–integration effort (CD–IE) hypothesis was successfully tested recently amongst large cohorts, wherein g and K either did not correlate, or where correlations could be controlled (Woodley, Figueredo, Brown, & Ross, 2013).

Spearman’s Law of Diminishing Returns (SLODR) is a similar phenomenon to CD–IE; however, it refers to the ability differentiation effect among persons of high g, (e.g., Detterman and Daniel, 1989, Spearman, 1927). Many individual-differences studies employing sample polytomization techniques have investigated SLODR over the last century, and the results of meta-analysis suggest that it is a real phenomenon, albeit one exhibiting a small effect magnitude (Hartmann & Nyborg, 2004). This phenomenon has also been found using polytomization at the population-differences level (Coyle & Rindermann, 2013).

SD–IE (strategic differentiation–integration effort) is an analogous effect to both CD–IE and SLODR; however, it concerns differentiation among components of life history. SD–IE exists among individuals (Figueredo, Woodley, Brown, & Ross, 2013) and populations (Fernandes and Woodley, 2013, Woodley and Fernandes, 2014, Woodley et al., 2014).

In the present study, we test SD–IE using regional-level data for counties in Spain and Italy. We also tested CD–IE and SLODR among these counties. At the between-group level, however, g and K are typically strongly correlated (e.g., Boutwell et al., 2013, Meisenberg and Woodley, 2013, Rushton, 2000, Templer, 2008), so it is hard to test CD–IE on the group level without the possibility of contamination from SLODR. We expect, based on the previous studies aforementioned, that among populations, SD–IE is present, and that either CD–IE or SLODR (or both) is present. We will discuss the generalities and particularities of these differentiation phenomena in Spain and Italy, as compared to previous similar tests in the US and in Japan, based on an ethnic-historical perspective.