Uncertainty exerts powerful influences on life history decisions. This has been demonstrated in experiments on nonhumans and in mathematical models. Studies of human populations are suggestive of the effects of uncertainty, but they rely on measures of environmental stress. In this paper, we derive a new measure of uncertainty, upsilon (υ), for use in non-experimental studies. We estimate its association with reproductive behaviors in a longitudinal panel sample of adolescents in the United States. Results show upsilon’s internal structure is consistent (...) with theoretical models of uncertainty. Its associations with reproductive outcomes are also consistent with theoretical predictions. Upsilon seems to have its largest effect on the timing of fertility—increasing the odds of early fertility by a factor of 7, net of the effects of control variables. We discuss our findings for the association between υ and the timing of reproductive effort as well as our future research on υ. (shrink)

Life history theory suggests that in risky and uncertain environments the optimal reproductive strategy is to reproduce early in order to maximize the probability of leaving any descendants at all. The fact that early menarche facilitates early reproduction provides an adaptationist rationale for our first two hypotheses: that women who experience more risky and uncertain environments early in life would have (1) earlier menarche and (2) earlier first births than women who experience less stress at an early age. Attachment theory (...) and research provide the rationale for our second two hypotheses: that the subjective early experience of risky and uncertain environments (insecurity) is (3) part of an evolved mechanism for entraining alternative reproductive strategies contingent on environmental risk and uncertainty and (4) reflected in expected lifespan. Evidence from our pilot study of 100 women attending antenatal clinics at a large metropolitan hospital is consistent with all four hypotheses: Women reporting more troubled family relations early in life had earlier menarche, earlier first birth, were more likely to identify with insecure adult attachment styles, and expected shorter lifespans. Multivariate analyses show that early stress directly affected age at menarche and first birth, affected adult attachment in interaction with expected lifespan, but had no effect on expected lifespan, where its original effect was taken over by interactions between age at menarche and adult attachment as well as age at first birth and adult attachment. We discuss our results in terms of the need to combine evolutionary and developmental perspectives and the relation between early stress in general and father absence in particular. (shrink)

Within evolutionary biology, life-history theory is used to explain cross-species differences in allocation strategies regarding reproduction, maturation, and survival. Behavioral scientists have recently begun to conceptualize such strategies as a within-species individual characteristic that is predictive of behavior. Although life history theory provides an important framework for behavioral scientists, the psychometric approach to life-history strategy measurement—as operationalized by K-factors—involves conceptual entanglements. We argue that current psychometric approaches attempting to identify K-factors are based on an unwarranted conflation of functional descriptions and (...) proximate mechanisms—a conceptual mix-up that may generate unviable hypotheses and invites misinterpretation of empirical findings. The assumptions underlying generic psychometric methodology do not allow measurement of functionally defined variables; rather these methods are confined to Mayr’s proximate causal realm. We therefore conclude that K-factor scales lack validity, and that life history strategy cannot be identified with psychometrics as usual. To align theory with methodology, suggestions for alternative methods and new avenues are proposed. (shrink)

The current paper synthesizes theory and data from the field of life history (LH) evolution to advance a new developmental theory of variation in human LH strategies. The theory posits that clusters of correlated LH traits (e.g., timing of puberty, age at sexual debut and first birth, parental investment strategies) lie on a slow-to-fast continuum; that harshness (externally caused levels of morbidity-mortality) and unpredictability (spatial-temporal variation in harshness) are the most fundamental environmental influences on the evolution and development of LH (...) strategies; and that these influences depend on population densities and related levels of intraspecific competition and resource scarcity, on age schedules of mortality, on the sensitivity of morbidity-mortality to the organism’s resource-allocation decisions, and on the extent to which environmental fluctuations affect individuals versus populations over short versus long timescales. These interrelated factors operate at evolutionary and developmental levels and should be distinguished because they exert distinctive effects on LH traits and are hierarchically operative in terms of primacy of influence. Although converging lines of evidence support core assumptions of the theory, many questions remain unanswered. This review demonstrates the value of applying a multilevel evolutionary-developmental approach to the analysis of a central feature of human phenotypic variation: LH strategy. (shrink)