Sociality, Hierarchy, Health Comparative Biodemography: A Collection of Papers (2014) / Chapter Skim
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4 The Long Reach of History: Intergenerational and Transgenerational Pathways to Plasticity in Human Longevity--Christopher W. Kuzawa and Dan T.A. Eisenberg
4 The Long Reach of History: Intergenerational and Transgenerational Pathways to Plasticity in Human Longevity--Christopher W. Kuzawa and Dan T.A. Eisenberg
Pages 65-94
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From page 65... ...
Although an unusually long lifespan is a defining characteristic of Homo sapiens, prehistoric and historic evidence for trends in human life expectancy, along with contemporary disparities in relation to ethnicity, class, and race (Keppel et al., 2002) , demonstrate the enormous impact of environments as influences on heterogeneity in potential longevity among members of the species.
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From page 66... ...
risk is not limited to abnormally low birth weight individuals, but is found in relation to increases in BW across the full BW spectrum, suggesting that the overall quantity of nutrition that a fetus receives may be important. In parallel, an extensive nonhuman literature has replicated many of these findings in model species using experimental designs, demonstrating that early environments, per se, are likely important drivers of many of these effects.
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From page 67... ...
For bio emography, this work implies that a full understanding of the determi d nants of human life expectancy, including the vast heterogeneity across and within societies, may require investigating not only the role of early rearing environments, but also historical environments experienced by ancestors, potentially extending back multiple generations. In this paper, we begin by briefly tracing the history of scientific interest in the early-life determinants of late-life health.
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From page 68... ...
Animal model work provides true experimental tests of the hypothesis that early-life experiences shape future adult health. Such studies have replicated many of the disease outcomes found in relation to lower BW in human populations (Symonds et al., 2003)
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From page 69... ...
. Maternal experiences during or prior to pregnancy have similarly been shown to predict altered epigenetic markings in human offspring, supporting a role for such effects on human biology and disease (Heijmans et al., 2008; Waterland et al., 2010)
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From page 70... ...
. To date, these intergenerational effects have received little research attention among demographers, despite their potentially large impacts on patterns of health and life expectancy within and between societies.
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. Evidence that maternal overweight can directly impact offspring a diposity and metabolic disease risk is seen in the excess estimated heritability for body mass index observed through mother-offspring pairs compared to father-offspring pairs (Murrin et al., 2012)
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From page 72... ...
Intriguingly, in part as a result of these epigenetic modifications, female offspring are biased towards exhibiting the same style of maternal care that they experienced as pups, thereby contributing to the intergenerational transmission of an environmentally induced behavioral phenotype. Intergenerational Pathway #2: Direct Germ Line Epigenetic Inheritance In a second class of nongenetic inheritance, a variety of epigenetic factors capable of directly regulating gene expression are modified in the parent in response to their experiences and then transferred via sperm or egg to offspring (and potentially, grand and great-grandoffspring)
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From page 73... ...
Early evidence for such transgenerational epigenetic transmission of environmental effects through the germ line came from animal models involving exposure to toxins and chemical compounds. In rats, exposure to endocrine-disrupting chemicals has been shown to impair the fertility of offspring (F1)
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From page 74... ...
. Human Evidence for Germ Line Epigenetic Inheritance of Environmental Effects Although animal experiments provide important biological precedents illustrating how the environment can impact subsequent generations, the relevance of these findings for understanding human biology and health remains unclear.
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From page 75... ...
predicting higher BMI in male, but not female offspring. The authors concluded that these findings, viewed alongside those of Överkalix, provide evidence that the "slow-growth period" of late childhood is a critical period in epigenetic programming in humans.
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From page 76... ...
. These findings raise the intriguing and testable hypothesis that societal trends toward delayed age at male reproduction may themselves lead to the transmission of longer telomeres that contribute to a lengthening of late-life function and life expectancy -- and conversely that earlier ages at male reproduction will lead to shorter telomeres (Eisenberg and Kuzawa, 2013)
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From page 77... ...
In instances such as these, an experience must influence the body and then be communicated in molecular form to the germ line. In cases of transgenerational epigenetic inheritance, any induced changes must survive the normal erasing of germ line epigenetic marks that occurs during gametogenesis and at implantation.
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From page 78... ...
Intergenerational Phenotypic Inertia One challenge to the hypothesis of long-term anticipatory adaptation comes from the long duration of the human lifespan. Because humans typically live many decades, the ecological conditions experienced during a few months of early development, such as gestation or early infancy, may not serve as reliable cues of environments likely to be experienced in adult life (Kuzawa, 2005)
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From page 79... ...
. FIGURE 4-1 The intergenerational phenotypic inertia hypothesis.
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From page 80... ...
. INTERGENERATIONAL PLASTICITY: HYPOTHESES FOR BIODEMOGRAPHY The pathways for phenotypic and epigenetic inheritance that we reviewed could have substantial impacts on individual and population h eterogeneity in morbidity and mortality, including ongoing secular trends in life expectancy documented in high-income populations.
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From page 81... ...
KUZAWA AND DAN T.A. EISENBERG 81 Hypotheses: Phenotype-to-Phenotype Transmission Across Two Generations In some ways the most straightforward tests of intergenerational effects include examples in which early environments influence adult characteristics that have similar downstream effects on fetal or infant development in the next generation, which alters the gestational environment of offspring and thereby increases risk of these same phenotypes in grandchildren.
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From page 82... ...
Despite this, this pattern of findings is limited to a single population, and we are aware of no attempts to replicate them. The Överkalix findings lead to the prediction that favorable nutrition during the prepubertal "slow-growth period" of late childhood will increase risk for chronic disease, and reduce life expectancy, among same-sexed grandoffspring.
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From page 83... ...
disease risk and paternal grandfathers' (PGFs) late childhood experience only show an association with grandsons' (GSs)
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From page 84... ...
Because humans typically live decades rather than months or years, this implies that the types and magnitudes of environmental change that are relevant when orienting an individual human life will be different than for a member of a short-lived species. Consistent with this prediction, we recently showed that offspring of longer-lived species tend to experience comparably small changes in BW and adult disease risk in response to maternal diet restriction in pregnancy compared to offspring of smaller and shorter-lived species (see Kuzawa and Thayer, 2011)
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From page 85... ...
However, environmental chemicals, endocrine factors including stress hormone levels, infections, and other immunological causes are also implicated in fetal loss (Holman and Wood, 2001; Nepomnaschy et al., 2006)
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From page 86... ...
. Despite these recent advances, much more is known about the nature and health effects of these responses in animal model species than in h umans, and indeed, there is only minimal evidence for transgenerational epigenetic inheritance in human populations.
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American Journal of Physical Anthro pology, 152(Suppl.
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American Journal of Human Biology, 19(6)
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American Journal of Human Biology, 19(5)
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. Altered skel etal muscle fiber composition and size precede whole-body insulin resistance in young men with low birth weight.
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American Journal of Human Biology, 17(1)
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American Journal of Human Biology, 22(4)
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. Birth weight and risk of type 2 diabetes, abdominal obesity and hypertension among Chinese adults.
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From page 94... ...
. Early life origins of insulin resistance and type 2 diabetes in India and other Asian countries.
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