Behavioral and Brain Sciences最新文献

The two-tiered model proposed by Ellis et al. offers a compelling framework for understanding how extrinsic mortality (EM) sources shape life history strategies, including fertility. This commentary evaluates this model in light of modern fertility trends, identifies gaps in its current formulation, and proposes modifications to enhance its explanatory power in modern contexts.

The number and timing of births are strongly associated with the stability of available resources and the risk of extrinsic mortality. The authors suggest a verbal model to disentangle the relationship between these two variables. However, we challenge their assumption of a hierarchical relationship between these two predictors and propose that formal modelling of their interaction, within a developmental perspective, could further our understanding of how the reproductive strategies of women respond to environmental uncertainty.

This commentary expands Ellis et al.'s 2-tiered life history (LH) model by integrating shyness and insecure attachment as mediators of environmental adaptation. Shyness balances survival-reproduction trade-offs with mixed LH outcomes. Avoidant attachment accelerates LH strategies under harsh conditions; anxious attachment delays reproduction under unpredictable conditions. Incorporating social behaviors, which are related to survival and safety, enhances the model's applicability across behavioral domains.

Life-history theory is a valuable framework to derive predictions about species-level and population-level adaptations, but it says little about variation between the individuals within a population. Conflating these different aggregate levels constitutes a mereological fallacy and may yield wrong conclusions. I argue that formal models are necessary to disentangle the mechanisms underlying individual-level and population-level variation in life-history traits.

Our systematic analysis of operationalizations and conceptualizations of harshness (extrinsic mortality) and unpredictability in the (psychology) life history literature highlights that (1) employment of extremely diverse measures contributes to the confusion about the effect of harshness on life history traits and (2) few measures reflect energetic stress or ambient EM, such that Ellis et al.'s two-tiered model should motivate future research.

In this commentary, I highlight the challenge of incorporating the harshness-unpredictability framework into the two-tiered model. While the effects of energetic stress (first tier), which are mostly mediated through biological pathways, can be decomposed into harsh (high mean) and unpredictable (high variance) components, ambient cues to EM (second tier) blur this distinction because they often share the same psychological mediators.

While I applaud the effort that went into their article, I believe Ellis and colleagues' two-tiered theory of life history has three problems: (1) relying on a straw man argument; (2) limitations in their data; and (3) alternate theoretical explanations for their correlations. Failure to attend to these issues resulted in a more confident presentation of their conclusions than is warranted.

Ellis and colleagues propose that plasticity in human life history strategy (pubertal timing, reproductive pacing) is governed by energetic and mortality-cue related regulatory tiers. We feel that our published interpretation of these findings - that growth (and thus maturational timing) is energetically driven, while reproductive behaviors are largely free to vary independent of energetics - provides a more parsimonious interpretation of this work. The concept of tiers is mechanistically vague and introduces unnecessary complexity to this literature.

The two-tiered life history model remains inadequate in addressing how social factors (particularly cultural norms and religious beliefs) interact with biological determinants to shape life history strategies. This limitation significantly constrains the model's explanatory power when applied to certain historical demographic phenomena. We recommend introducing a third explanatory framework (the cultural-institutional tier) to augment the two-tiered model.

I argue that the two-tier model represents a clear step forward, resolving debates and disentangling complexity in our understanding of human life history strategies. I relate the model to findings from my previous work, as well as to embodied capital and market integration, providing relevant schematics. I then discuss the timing of exposure to mortality cues and the age of the deceased, discussing what the two-tier model does and does not add to these debates.