Unintentional error in formula preparation and its simulated impact on infant weight and adiposity.

BACKGROUND: Accelerated weight gain in infancy is a public health issue and is likely due to feeding behaviours. OBJECTIVES: To test the accuracy of individuals to dispense infant formula as compared with recommended serving sizes and to estimate the effect of dispensing inaccuracy on infant growth. METHODS: Fifty-three adults dispensed infant formula powder for three servings of 2, 4, 6, and 8 fl oz bottles, in random order. The weight of dispensed infant formula powder was compared with the recommended serving size weight on the nutrition label. A novel mathematical model was used to estimate the impact of formula dispensing on infant weight and adiposity. RESULTS: Nineteen percent of bottles (20 of 636) prepared contained the recommended amount of infant formula powder. Three percent were underdispensed, and 78% of bottles were overdispensed, resulting in 11% additional infant formula powder. Mathematical modelling feeding 11% above energy requirements exclusively for 6 months for male and female infants suggested infants at the 50th percentile for weight at birth would reach the 75th percentile with increased adiposity by 6 months. CONCLUSIONS: Inaccurate measurement of infant formula powder and overdispensing, which is highly prevalent, specifically, may contribute to rapid weight gain and increased adiposity in formula-fed infants.

Evolutionary game dynamics of controlled and automatic decision-making.

We integrate dual-process theories of human cognition with evolutionary game theory to study the evolution of automatic and controlled decision-making processes. We introduce a model in which agents who make decisions using either automatic or controlled processing compete with each other for survival. Agents using automatic processing act quickly and so are more likely to acquire resources, but agents using controlled processing are better planners and so make more effective use of the resources they have. Using the replicator equation, we characterize the conditions under which automatic or controlled agents dominate, when coexistence is possible and when bistability occurs. We then extend the replicator equation to consider feedback between the state of the population and the environment. Under conditions in which having a greater proportion of controlled agents either enriches the environment or enhances the competitive advantage of automatic agents, we find that limit cycles can occur, leading to persistent oscillations in the population dynamics. Critically, however, these limit cycles only emerge when feedback occurs on a sufficiently long time scale. Our results shed light on the connection between evolution and human cognition and suggest necessary conditions for the rise and fall of rationality.

Nonlinear dynamics of the rock-paper-scissors game with mutations.

We analyze the replicator-mutator equations for the rock-paper-scissors game. Various graph-theoretic patterns of mutation are considered, ranging from a single unidirectional mutation pathway between two of the species, to global bidirectional mutation among all the species. Our main result is that the coexistence state, in which all three species exist in equilibrium, can be destabilized by arbitrarily small mutation rates. After it loses stability, the coexistence state gives birth to a stable limit cycle solution created in a supercritical Hopf bifurcation. This attracting periodic solution exists for all the mutation patterns considered, and persists arbitrarily close to the limit of zero mutation rate and a zero-sum game.