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PAPERS: Barbara J M H Jefferis, Chris Power, and Clyde Hertzman Birth weight, childhood socioeconomic environment, and cognitive development in the 1958 British birth cohort study BMJ 2002; 325: 305 [Abstract] [Full text]

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Correlations and Causes

Fraank J Leavitt   (10 August 2002)

Unfortunately we are not born equal.

Russell Keenan   (12 August 2002)

Brain function may be determined by adverse environments in utero

Simon C Langley-Evans   (16 August 2002)

Correlations and Causes 10 August 2002
Fraank J Leavitt, Chairman, Centre for Asian and International Bioethics Faculty of Health Sciences, Ben Gurion University of the Negev, Beer Sheva, 84105, ISRAEL Send response to journal: Re: Correlations and Causes	The paper is a perfect example of what the philosophers call "post hoc, ergo propter hoc". The fact that two events are correlated does not entail that one causes the other. The paper gives no evidence that birth weight, social class and cognitive development, are not all results of a common fourth factor, like genetics. The statement: "The postnatal environment has an overwhelming influence", is particularly gratuitous because the paper cites no seperated-twin studies to show that social class is not genetically influenced.
Unfortunately we are not born equal. 12 August 2002
Russell Keenan, Consultant PAediatric Haematologist Alderhey Hospital Liverpool L12 Send response to journal: Re: Unfortunately we are not born equal.	The authors are a little quick to jump to the conclusion 'The postnatal environment has an overwhelming influence' (on mathematical acheivement). This conclusion is particularly problematic in the way this study has been reported in the lay press and will be interperated by politicians. The evidence provided suggests a more likely explanation which may be socially and politically unpalatable i.e. 'we are not born equal'. Few educationalists, and for that matter politicians, would argue that academic acheivement provides an improved chance of employment, income and in turn social class. Intelligence, however defined, has a multigenic hereditary component. The result is more intelligent children are more likely to raise their social class and pass these charateristics onto their own offspring. Unfortunately the opposite is true for less intelligent children.
Brain function may be determined by adverse environments in utero 16 August 2002
Simon C Langley-Evans, Lecturer in Human Nutrition University of Nottingham, School of Biosciences, Sutton Bonington, Loughborough LE12 5RD, UK Send response to journal: Re: Brain function may be determined by adverse environments in utero	This article adds to the growing body of literature that suggests that all aspects of physiological, metabolic, endocrine and probably neural function are subject to non-genetic influences before birth. Weight and other measures of physical attributes at birth are determined primarily by genetic inheritance. Other factors such as poor maternal nutrition, maternal stress or smoking can constrain that genetically defined growth. Constraints on growth force the fetus to adapt and these adaptations may become permanent features that modify tissue functions and possibly disease risk in later life [1]. The brain and its’ functions is no exception to this programming effect of the fetal environment. There is good evidence from human cohorts such as the offspring of women who were pregnant in the wartime Dutch Hunger winter to suggest that risk of mental illness [2] is increased by prenatal growth restraint. Similarly Barker et al [3] have proposed that depression and suicide are related to prenatal factors and growth in infancy. These data suggest that prenatal influences may alter the structure of the brain and neuroendocrine processes within key centres. Importantly a large number of animal studies back up these assertions. Rats exposed to prenatal undernutrition show alterations to the gross structure of the brain with redistribution of neurones between different centres [4]. A broad range of behavioural changes are noted in the offspring of rat mothers subject to prenatal stressors [5]. The findings of Jefferis and colleagues [6] are thus entirely consistent with a small but significant influence of the prenatal environment upon later learning and processing abilities. 1. DJP Barker. The fetal and infant origins of disease. Eur J Clin Invest 1995; 25: 457-463. 2. HE Hulshoff, HW Hoek, E Susser, AS Brown, A Dingemans, HG Schnack, NEM van Haren, LMP Ramos, CC Gispen de Wied, RS Kahn. Prenatal exposure to famine and brain morphology in schizophrenia. Am. J. Psychiatry 2000;157: 1170-1172. 3. DJP Barker, C Osmond, I Rodin, CHD Fall, PD Winter. Low weight gain in infancy and suicide in adult life. BMJ 1995; 311: 1203 4. A Plagemann, T Harder, A Rake, K Melchior, W Rohde, G Dorner. Hypothalamic nuclei are malformed in weanling offspring of low protein malnourished rat dams. J. Nutr. 2000; 130: 2582-2590 5. R Diaz, K Fuxe, SO Ogren. Prenatal corticosterone treatment induces long-term changes in spontaneous and apomorphine-mediated motor activity in male and female rats. Neuroscience 1997; 81: 129-140. 6. BJMH Jefferis, C Power, C Hertzman Birth weight, childhood socioeconomic environment, and cognitive development in the 1958 British birth cohort study. BMJ 2002; 325: 305