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12 Overview Thoughts on Genetics: Walking the Line Between Denial and Dreamland, or Genes Are Involved in Everything, But Not Everything Is "Genetic"--Kenneth M. Weiss
12 Overview Thoughts on Genetics: Walking the Line Between Denial and Dreamland, or Genes Are Involved in Everything, But Not Everything Is "Genetic"--Kenneth M. Weiss
Pages 231-248
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From page 231... ...
"Genetic" is also a population concept that refers to the correlation between phenotype variation and inherited variation in populations. Inherited variation in the p53 gene is associated with abnormal tissue architecture and cancer.
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From page 232... ...
Evolution involves population size, mating patterns, chance, migration, geographic and social distribution, differential reproduction, and the like. The variation that results depends on mutation rates, the size of the mutation target (number and length of relevant genetic units in the genome)
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From page 233... ...
The practical upshot is that many complex traits can be called "oligogenic" or "multilocus," in that embedded in a polygenic background are at least some specific loci with alleles frequent enough and/or effects strong enough that standard methods can detect them with adequate sample design -- and new instances are continually being reported. But what fraction of genetic architecture comprises this low-hanging fruit in relation to common disease risk is a contentious question.
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From page 234... ...
Hypertension refers to blood pressure elevated enough to pose a presumed universal risk factor for cardiovascular disease per se, not simply relative to the average in the population. In other words, everyone in the population is presumed to be at higher risk with higher blood pressure.
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From page 235... ...
Such a situation may involve genetic mechanism but not be mappable in observational research: if we all share the genetic mechanism, there may be insufficient or genetic variation contrasts that are too heterogeneous for statistical inference. This usually points to exogenous causal factors, like diet, and does not mean the trait is genetic in the sense that variation in genetic susceptibility is a major cause of variation in risk.
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From page 236... ...
A potential complicating factor is a third aspect of genetic causation mentioned earlier, that of somatic mutation. We don't yet know how important this may be, but somatic mutation is probably responsible for cases of behavior disorders related to epilepsy and may be a sleeping giant in behavioral biology that will be silent until attacked explicitly, which is difficult to do with today's technologies (Weiss 2005a, 2005b)
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From page 237... ...
Overall, to varying but not precisely known extents, about 30-60 percent of the variance in most complex traits, including chronic disease, generally called the heritability, is due to aggregate effects of genetic variation that can be estimated statistically by familial aggregation of risk, monozygotic versus dizygotic twin contrasts, and other common measures. Family-based estimates are probably somewhat inflated because of undetected confounding between environmental and genetic correlations (various study designs, such as adoptee studies, are often suggested to try to disentangle these)
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From page 238... ...
The genetic objective is to predict outcome from inherited genotype. Part A shows a symbolic DNA sequence with several alleles in fonts proportional to their inherent effect on some trait of interest (inherent effect is a rather epistemologically dubious notion itself, but we'll let it pass)
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From page 239... ...
Snatching victory from failure We do not yet know clearly where on the spectrum from monogenic to polygenic control the genetic components of complex traits lie, and this clearly varies among traits and to some extent among different populations because of their different population history. There are two possible explanations for the frustration we have faced in attempting to dissect complex traits into their genetic and environmental causes or to identify the factors when they interact.
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From page 240... ...
Current knowledge raises the epistemological and methodological question of what to do in the face of a substantial fraction of polygenic control, rather than hoping, against the bulk of the existing evidence, that we can identify a large fraction of individual contributing genes with expensive technological fixes, such as more elaborate statistics, more extensive genotyping technology, and faster computers. Denial vERSUs Dreaming The substantial debate about the nature and extent of genetic control of complex traits becomes more heated when the subject is social or nonpathogenic behavioral traits.
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From page 241... ...
But since natural selection affects only genes that determine a trait, Darwinian arguments are inescapably deterministic. Where between these views -- one denying genetic involvement in social behavioral traits, and the other dreaming of a simple causal world -- does the truth lie?
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From page 242... ...
It remains relevant to ask what the scientific rationale is that leads social scientists today to hunger yet again for rescue by aliens, in this case molecular rescue by genes, another reductionist approach that is too far below the emergent level of the phenomena to fully explain them, and a diversion from trying to fix the problems in social science itself. Why would social scientists essentially abandon the notion that social facts are to be understood in their own terms and instead seek to reduce these facts to molecular terms?
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From page 243... ...
Topics discussed in this volume concern genetic contributions to behavioral traits that may be ultimately related to aspects of health but only indirectly so. Behavioral genetic findings also apply to those that the subject interacts with.
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From page 244... ...
There is often a disclaimer that a given kind of social genetics is just exploration of the nature of nature, to build models of basic mechanism that can't be done through mouse experiments, and that the work is not intended to identify individuals for policy reasons, nor is understanding mechanism necessarily a step toward genetic determinism in the variation sense. But read carefully: do the same authors -- even the same paper -- eventually relate their findings to points of intervention?
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From page 245... ...
What about selective abortion based on genetic results for behavioral traits? How undesirable a behavioral trait might be involves subjective judgments or values, which can delve into senses of personal worth, and there are countless ways in which societal discrimination could be imposed on those deemed inherently less worthy.
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From page 246... ...
There are positive findings that may help in the understanding of genetic mechanisms affecting social behavior, but even classic examples of success, like ApoE, have subtleties that may be important to take into account. Extensive data from research on complex disease traits, which one might think would be more tractable than behavioral traits, suggests that a lot of effort, time, distraction, and resources will be committed to chasing down false positive results if the studies are not properly designed to detect genetic factors or if due attention is not paid to tempering results.
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From page 247... ...
KENNETH M WEISS 247 Odling-Smee, F.J., Laland, K.N., and Feldman, M.W.
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