BackgroundInterventions to promote healthy eating make a potentially powerful contribution to the primary prevention of non communicable diseases. It is not known whether healthy eating interventions are equally effective among all sections of the population, nor whether they narrow or widen the health gap between rich and poor.We undertook a systematic review of interventions to promote healthy eating to identify whether impacts differ by socioeconomic position (SEP).MethodsWe searched five bibliographic databases using a pre-piloted search strategy. Retrieved articles were screened independently by two reviewers. Healthier diets were defined as the reduced intake of salt, sugar, trans-fats, saturated fat, total fat, or total calories, or increased consumption of fruit, vegetables and wholegrain. Studies were only included if quantitative results were presented by a measure of SEP.Extracted data were categorised with a modified version of the “4Ps” marketing mix, expanded to 6 “Ps”: “Price, Place, Product, Prescriptive, Promotion, and Person”.ResultsOur search identified 31,887 articles. Following screening, 36 studies were included: 18 “Price” interventions, 6 “Place” interventions, 1 “Product” intervention, zero “Prescriptive” interventions, 4 “Promotion” interventions, and 18 “Person” interventions.“Price” interventions were most effective in groups with lower SEP, and may therefore appear likely to reduce inequalities. All interventions that combined taxes and subsidies consistently decreased inequalities. Conversely, interventions categorised as “Person” had a greater impact with increasing SEP, and may therefore appear likely to reduce inequalities. All four dietary counselling interventions appear likely to widen inequalities.We did not find any “Prescriptive” interventions and only one “Product” intervention that presented differential results and had no impact by SEP. More “Place” interventions were identified and none of these interventions were judged as likely to widen inequalities.ConclusionsInterventions categorised by a “6 Ps” framework show differential effects on healthy eating outcomes by SEP. “Upstream” interventions categorised as “Price” appeared to decrease inequalities, and “downstream” “Person” interventions, especially dietary counselling seemed to increase inequalities.However the vast majority of studies identified did not explore differential effects by SEP. Interventions aimed at improving population health should be routinely evaluated for differential socioeconomic impact.Electronic supplementary materialThe online version of this article (doi:10.1186/s12889-015-1781-7) contains supplementary material, which is available to authorized users.

Repeatability of parental care, let alone heritability of care, has been rarely measured, although there has been much research linking sexual selection to male parental care and also examining biparental care in relation to game theory models. We investigated within‐ and between‐year repeatabilities of incubation and nestling provisioning and how these two types of parental care were related in a sexually dimorphic species, the house sparrow, Passer domesticus. We found that between‐ and within‐year repeatabilities of feeding rate were high in males and low to moderate in females, but that between‐ and within‐year repeatabilities of incubation time were low to moderate in both sexes. Interestingly, the amount of time during which neither sex incubated significantly predicted the subsequent male feeding rate but not the female feeding rate. Our results suggest a need for a new theoretical framework that encompasses variation in the predictability and plasticity of parental investment by individuals.

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Maternal fitness should be maximized by the optimal division of reproductive investment between offspring number and offspring quality. While evidence for this is abundant in many taxa, there have been fewer tests in mammals, and in particular, humans. We used a dataset of humans spanning three generations from preindustrial Finland to test how increases in maternal fecundity affect offspring quality and maternal fitness in contrasting socio-economic conditions. For 'resource-poor' landless families, but not 'resource-rich' landowning families, maternal fitness returns diminished with increased maternal fecundity. This was because the average offspring contribution to maternal fitness declined with increased maternal fecundity for landless but not landowning families. This decline was due to reduced offspring recruitment with increased maternal fecundity. However, in landowning families, recruited offspring fecundity increased with increased maternal fecundity. This suggests that despite decreased offspring recruitment, maternal fitness is not reduced in favourable socio-economic conditions due to an increase in subsequent offspring fecundity. These results provide evidence consistent with an offspring quantity-quality trade-off in the lifetime reproduction of humans from poor socio-economic conditions. The results also highlight the importance of measuring offspring quality across their whole lifespan to estimate reliably the fitness consequences of increased maternal fecundity.

Human menopause is ubiquitous among women and is uninfluenced by modernity. In addition, it remains an evolutionary puzzle: studies have largely failed to account for diminishing selection on reproduction beyond 50 years. Using a 200-year dataset on pre-industrial Finns, we show that an important component is between-generation reproductive conflict among unrelated women. Simultaneous reproduction by successive generations of in-laws was associated with declines in offspring survivorship of up to 66%. An inclusive fitness model revealed that incorporation of the fitness consequences of simultaneous intergenerational reproduction between in-laws, with those of grandmothering and risks of dying in childbirth, were sufficient to generate selection against continued reproduction beyond 51 years. Decomposition of model estimates suggested that the former two were most influential in generating selection against continued reproduction. We propose that menopause evolved, in part, because of age-specific increases in opportunities for intergenerational cooperation and reproductive competition under ecological scarcity.