Difficulties identifying causally relevant genetic variants underlying patterns of human variation have been given competing interpretations. The debate is illuminated in this article by drawing attention to the issue of underlying heterogeneity—the possibility that genetic and environmental factors or entities underlying a trait are heterogeneous—as well as four other fundamental gaps in the methods and interpretation of classical quantitative genetics:
Social epidemiologist Davey Smith (2011) argues that epidemiologists should accept a gloomy prospect: considerable randomness at the individual level means that they should keep their focus on modifiable causes of disease at the population level. The difficulty epidemiology has had in moving from significant population-level risk factors to improved prediction of cases at an individual level is analogous to the lack of success in the search for systematic aspects of the non-shared environmental influences that human quantitative genetics claims overshadow common environmental influences (e.g., the family’s socioeconomic status which siblings have in common). This article responds to the argument and analogy, aiming to draw three audiences—social epidemiologists, human quantitative geneticists, and philosophers of science—into a shared discussion that centers not on randomness, but on heterogeneity in various forms.
My four steps to interpret and move beyond nature-nurture for the current draft of a 1500-word entry for a handbook on environmental studies: Continue reading
Practice run of a talk to philosophers of biology & biologists, March 2016 Continue reading
The first installment ended on the following note: Suppose you have many sets of same-sex non-identical twins raised together and many sets of same-sex identical twins raised together and find that the identical twins are on average more similar. It seems reasonable to conclude that is because they share all their genes whereas the non-identical twins share fewer of their genes. Reasonable, but not certain, at least not certain that it is only about genes. After all, the treatment of identical twins could be more similar than the treatment of non-identical twins, even same-sex non-identical twins. In any case, that conclusion doesn’t say that it’s the same nature—the same genes—or the same nurture that brings about the resemblance from one pair of twins to the next. Given this possibility of underlying heterogeneity where are you? What can you do? Continue reading
Genetic heterogeneity refers to
either: a) a multiplicity of mutations within some gene and a spectrum of corresponding values for a trait (or “phenotype”), each of which varies little within the typical range of locations (i.e., allelic heterogeneity); or b) the trait exists if any one of a range of loci has the atypical form (i.e., locus heterogeneity).
If presence of a section of DNA (SNP) increases the odds of a disease, then look for genes close to the SNP, investigate the enzymes associated with the gene and use that as an entry point to investigation of the etiology of the disease, then try to design drug therapies to counteract any undesired function of those enzymes or their subsequent effects. Continue reading