Farther off from England but no nearer France

Why children in the same family are so different from one another must be a question that has intrigued most of us at some point. We understand, or think we understand, differences in physical characteristics ‘she’s the spitting image of her Dad’, although the variance explained by single nucleotide polymorphisms in genome-wide association studies for characteristics as heritable as height has only recently moved from <5 to 45%. However, it seems obvious that other less easily defined characteristics, such as personality, will have a large environmental input. How did the Mitford family (Figure 1) end up producing Diana the Fascist and Jessica the Communist? How did the sons and daughters of Violeta Chamorro, president of Nicaragua 1990–1997, end up on opposing sides during the civil war that preceded their mother’s election? The classic paper by Plomin and Daniels reprinted in the current issue of the IJE brought together evidence of the importance of non-shared environments in the development of personality, psychopathology and differences in cognitive ability between children within families. This represented a major challenge to the existing paradigm at a time when the debate raged almost exclusively between nature and nurture and where nurture was taken to mean the shared environment. However, as Neven Sesardic points out in his commentary, reaction to this evidence was notable by its absence. Although it seems that there are no serious challenges to the claim for primacy of the non-shared environment, progress in determining which variables account for this non-shared variability has been very limited. In general, although Plomin himself feels this research is off to a good start and documents evidence from over a dozen studies of small non-shared environmental effects independent of genetics and shared environments, the wider jury seems to be firmly of the opinion that we are closer to the ‘gloomy prospect’ of chance as the source of non-shared environmental influence, as outlined in Plomin and Daniels’ original paper, than ‘the cup [. ] more than one quarter full’. The number of published meta-analyses in epidemiology has increased exponentially since the early 1990s—see Figure 2. Reflecting this increasing trend, the current issue of the IJE contains five empirical meta-analysis papers, and a methodological paper. About half the world’s population is exposed to smoke from household use of solid fuel; mainly coal and various forms of biomass. Hosgood et al. summarize the association between household coal use for heating and cooking and lung cancer in 25 studies, of which 20 are from mainland China or Taiwan, where coal use is very common. Firm evidence of an association between coal use and lung cancer was observed in 17 of the 20 studies with considerable variation across regions of China, suggesting that carcinogenic properties of the coal and personal exposure vary by region and are not explained by smoking; a 3-fold risk of lung cancer being observed among women non-smokers. The UK Clean Air Act of 1956 was brought in after the huge increase in deaths that occurred during and after the great smog in London in 1952. Judging from the last Olympics, smog is still a problem in China, and in a succinct and pertinent commentary, Nino Kunzil suggests that ‘dilution [. ] is not the solution’; rather than fitting chimneys, coal stoves should be replaced by electric. High body mass index, the top-ranking risk factor for Type II diabetes, is more prevalent in lower socio-economic groups in high-income countries. However, despite some indication that obesity may be on the rise among lower socio-economic groups Figure 1 Jessica, Nancy, Diana, Unity and Pamela Mitford in 1935. Reproduced by kind permission of Rogers Coleridge and White Published by Oxford University Press on behalf of the International Epidemiological Association