Evolutionary Trade-Offs: Emergent Constraints and Their Adaptive Consequences.

Abstract

Evolutionary trade-offs: emergent constraints and their adaptive consequences

Trade-offs are widely recognized in biology, but the rules that govern them are not yet well understood. Increased predictive power can be gained by treating trade-offs as emergent phenomena governed by laws that are also emergent. The law-like nature of trade-offs becomes evident when we subdivide examples by type.

Trade-offs can be A) probabilistic (e.g. the darkest individual in a population will rarely be the biggest), B) based on the mutually exclusive allocation of resources (e.g. roots vs. shoots), or C) based on extrinsic design limitations (e.g. high efficiency vs. extreme robustness). Only design trade-offs are law-like, although the other two types may be transformed into design limitations given strong selective pressures.

Between every two fitness-enhancing characteristics of an organism or mechanism, a design trade-off must logically exist, preventing simultaneous optimization. Selection’s tendency toward optimization reveals that fraction of design trade-offs we come to empirically recognize. A particular trade-off can be evident both within and between species. Trade-offs may be obscured by insufficient selective time, noisy or fluctuating selective environments, and weak selection pressures.

A natural parallel exists between trade-offs in space, and in time. The interrelation between these phenomena on the one hand, and niche-partitioning, competitive exclusion, character displacement and phenotypic plasticity on the other is also considered.

Chapter One describes the proposed theoretical landscape. Chapter Two describes a senescence-causing trade-off between cancer prevention and tissue-repair capacity in vertebrates. Chapter Three relates the latitudinal diversity gradient to a gradient of design constraints that is a consequence of environmental fluctuation positively correlated with latitude on all relevant time scales. A natural reconciliation between niche assembly and community drift is proposed, and the effects of mate choice on diversity patterns is considered. Chapter Four argues that facultative human moral self-restraint is an evolutionary response to an inescapable trade-off between the component of fitness that results from success in competition within one’s lineage, and the component that derives from the success of one’s group in competition with other lineages.