Prenatal environment

Disturbance of the prenatal environment by stressing the mother can lead to increased CRH gene expression in the fetal PVN (Fujioka et al. 1999) and... 

What is certainly true is that you don t need great drama— earthquakes or floods or terrorism—to affect the prenatal environment. Far subtler events can have an impact on that environment as well. 

What s the science that directs us to consider the prenatal environment so important in childhood and adult behavior The evidence and conclusions have been accumulating for more than a decade and form the substance of this book. Some highlights ... 

These and a host of other studies since the early 1990s, research to be discussed in this book, all point to a new attitude in biological and medical science—a new understanding that the prenatal environment is an extremely important determinant of health, disease, IQ and behavior. 

In Part II, we consider some of the postnatal costs of those influences and examine the strong evidence that the prenatal environment is related to various behavioral dysfunctions or anomalies and to deficits in intelligence. The chapters in this part cover fetal alcohol disorders, transsexuality, developmental disabilities such as attention deficit hyperactivity disorder (ADHD), autism, and psychosis, as well as the emotional frameworks that give rise to a few other mental disorders. The important question of individual IQ is also addressed, including the controversies about its measurement in IQ tests (what are such tests Do their scores signify anything How is their reputed significance used ) and the extent to which the prenatal environment comes into play in the variance of IQ. 

In Part III, we move past the individual costs of prenatal disruptions to address broader social and economic questions that relate to those costs. What, for example, are the effects of ethnic and cultural heritage, geographic location, and socioeconomic status on the prenatal environment The chapter in this part also seeks to answer questions about the relation between prenatal impacts and social behavior such as criminality. 

My intention throughout the book is to make the case that the prenatal environment must be considered in any attempt to understand the origins of human health and disease, and of human behavior and intelligence, and in any resolution of the simplistic nature—nurture debate put to the public by the media. Nature is more than genetics, and nurture is a more complex proposition than what occurs in just the postnatal environment of parents and communities and nations. Environment starts at conception, and neglecting this fact as we have for too long has resulted in often tragic consequences for those born into our world and, by extension, for us all. 

America currently has a heavy bundle of social, economic, and political problems related to the prenatal environment, but... 

Of importance is that some hereditarian psychometricians are fond of measuring behavioral and IQ differences between various racial and ethnic groups and then offering us conclusions about how genes determine behavior and IQ.17 Do such psychometric studies of heritability of behavior and IQ involve adequate controls for prenatal environment They do not. 

I have considered lead pollution in detail, but lead is not the only villain in the prenatal environment. Others include methyl-mercury polychlorinated biphenyls (PCBs) dioxins pesticides ionizing radiation and maternal use of alcohol, tobacco, marijuana, and cocaine. These villains can cause a range of behavioral effects from severe mental retardation and disability to subtle changes in mental function that depend on the timing and dose of the chemical agent. Indeed, more than zoo industrial... 

The second set of variables lies in the prenatal environment. These are variables that the mother either produces (her own hormones, for example) or filters from external sources (tobacco-smoke chemicals, for example) into the placenta and the local environments of prenatal tissues. During gestation,... 

Yes, genes ultimately control development, but the control is not simplistic. These days the most important idea in developmental biology is that it s the switching of genes on and off (expression or prevention of expression) that determines the direction development takes at any instant in the embryo and fetus, and that the switching is heavily dependent on interactions with both local tissue environments and the global prenatal environment. 

The important point here is that the production and migration of nerve cells are provoked by local biochemical events easily affected by the local prenatal environment, and the same is true for axon guidance processes that connect nerve cells to other nerve cells—connections of critical importance for later cognitive and emotional behavior. 

There is no evidence to argue that the other half result from prenatal environmental effects. But it s reasonable to assume that the prenatal environment in its various forms can be an important factor, and that countless possibilities exist for both lethal and nonlethal effects due to that factor. The simple fact that so many embryos are apparently lost means embryos are particularly vulnerable to damage. 

As in every other biological system, fetal mechanisms to sustain survival by compensating for various environmental effects do exist. But as with other biological systems, survival mechanisms often involve a trade-off between a severe outcome and a lesser outcome. The fetus survives, but with a mild consequence recognized only as phenotypic variation —a difference between individuals that results not from genetic differences or postnatal environmental differences, but from differences in prenatal environments. 

In 1996, researchers reported intellectual impairment (in short-term memory, long-term memory, and sustained attention) in school children exposed to PCBs in utero.42 The data showed that in the prenatal environment the presence of PCBs in concentrations only slightly higher than those in the general environment can have a long-term impact on intellectual function. In addition, the deficits in short-term memory in infancy and early childhood are consistent with reports of reduced IQ scores of children in Taiwan whose mothers had ingested rice oil contaminated with PCBs and dibenzofurans... 

What seems apparent from all these cases is that human sexuality is a good example of how genes, prenatal environment, and postnatal environment all contribute to behavior traits. As such, absolute genetic determinism of gender seems an untenable idea. Both genes and environment are involved—prenatal and postnatal environment—and how they re involved may differ in each case. 

Nor are genes and heredity the exclusive determinants of sexual orientation, which is instead derived from a complex of variables involving genes, prenatal environment, and postnatal environment. Four real empirical situations illustrate variations of this point. 

The best view we have from twin studies is that schizophrenia results from both genetic and shared-environment etiological influences, with shared environment meaning classical postnatal environmental factors plus prenatal environmental factors, such as exposure to infectious agents, macro- or micronutrient dietary characteristics, and exposure to environmental toxins, teratogens, and other assaults to the prenatal environment.22 Which factors and assaults are important can differ from one individual to another for reasons still unknown. Schizophrenia is not a simple puzzle. 

A study of 20,000 pregnant women in California, begun in the 1990s, has been yielding data about the relation between prenatal environment and the risk for adult onset schizophrenia spectrum disorders (SSDs). Results indicate that first trimester... 

This chapter is about the effects of the prenatal environment on childhood and adult intelligence quotient (IQ), but it needs to be more than that, since once the prenatal environment is admitted as an important determinant of postnatal behavior and cognitive performance, some old hereditarian ideas must be abandoned. Abandonment of these old ideas will be a critical step forward in the twenty-first century, and I want to outline here the reasons for the shift among researchers. The problem for the general reader is that although the new view of IQ involves concepts in statistics and psychometrics, I have committed myself to tell the story without graphs or equations. I do hope this works for the general reader, but if in a few places the discussion seems too technical, I advise the reader... 

Meanwhile, the current pervasive myth about IQ is that it s an innate and inherited trait, determined by genes and with no or only minor influences by the individual s environment. The myth is substantially based on a set of mistaken ideas,1 one of which imagines that babies pop out as immaculate gestations and that individual IQ is unaffected by the prenatal environment. 

The clearest refutation of the idea advanced by hereditarian behavior geneticists that the prenatal environment is of only small consequence for childhood and adult IQ is the research on known IQ effects of prenatal exposure to certain neurotoxins. Any argument that this neurotoxic impact is extreme, rare, and therefore irrelevant is unsound. In addition, every known neurotoxic effect confirms the possible prenatal impact of other environmental agents not yet studied, and we do know there are literally hundreds of such neurotoxins already dispersed in the environment.15... 

Definitely not. The similar environments in these studies is the postnatal environment. The prenatal environment is never considered in the analysis. For twins reared in similar postnatal environments, we don t know if the higher twin-pair IQ correlations for MZ twins are due to identity of genes or similarity of fetal environments. It is certainly possible that the fetal environments (including reactions to impacts) of identical twins are always more similar than the fetal environments of fraternal twins. We don t know enough yet about human twin biology to discount that possibility. 

The general constraint on the interpretation of all twin studies is that differential effects of culture, family, and prenatal environments, and even the effects of their physical appearance on the correlated experience of twins, all affect twin development.31... 

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