Interventions 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). We 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”. Our 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. Interventions 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.

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.

The black throat patch or bib of male house sparrows, Passer domesticus, is often referred to as a “badge of status” or a “badge” because previous studies have shown bib size to be correlated with the social status of males. Yet, little is known about how strong and robust this relationship is and how the strength of this relationship compares with that of other associations. We conducted a meta-analysis for 6 well-studied correlates of bib size: fighting ability, parental ability (egg incubation and food provisioning), age, body condition, cuckoldry, and reproductive success. We introduce a flexible meta-analysis method in this study that is better suited in the biological sciences than the methods usually employed in popular meta-analysis software because our method accounts for a common form of nonindependence of the data. The relationship between fighting ability and bib size was found to be strong and robust, and the relationship between age and bib size was moderate and robust. Also, body condition was weakly but significantly correlated with badge size. The other parameters showed nonsignificant small effects and/or large confidence intervals. Therefore, we conclude that bib size signals dominance and to a lesser extent age and possibly reflects body condition in house sparrows. There was weak evidence that bib size is currently under sexual selection because there was little association between reproductive success and bib size. This is surprising as the bib size probably affects the outcome of male–male competition. Empirical data on sparrow bib size could not be reconciled with sexual selection theory, although there is ample evidence that it is a condition-dependent trait.

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 pre-industrial 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.

In the past six decades, lifespan inequality has varied greatly within and among countries even while life expectancy has continued to increase. How and why does mortality change generate this diversity? We derive a precise link between changes in age-specific mortality and lifespan inequality, measured as the variance of age at death. Key to this relationship is a young–old threshold age, below and above which mortality decline respectively decreases and increases lifespan inequality. First, we show for Sweden that shifts in the threshold’s location have modified the correlation between changes in life expectancy and lifespan inequality over the last two centuries. Second, we analyze the post–World War II (WWII) trajectories of lifespan inequality in a set of developed countries—Japan, Canada, and the United States—where thresholds centered on retirement age. Our method reveals how divergence in the age pattern of mortality change drives international divergence in lifespan inequality. Most strikingly, early in the 1980s, mortality increases in young U.S. males led to a continuation of high lifespan inequality in the United States; in Canada, however, the decline of inequality continued. In general, our wider international comparisons show that mortality change varied most at young working ages after WWII, particularly for males. We conclude that if mortality continues to stagnate at young ages yet declines steadily at old ages, increases in lifespan inequality will become a common feature of future demographic change.