Proximate versus Ultimate Effects of Intervention. Anthropologists often point out that in the PTC taste blindness polymorphism there are nil frequencies of non-tasters among many recent hunting peoples, but high non-taster frequencies in cosmopolitan areas, where humans have been longer removed from a foraging subsistence (Boyce et al., 1976; Pool, 1992) (see PTC tasting in Table 1 of the entry Genetic Disease II).12
The classic explanation for this observation is that modernization provides both enhanced tools and special environments in which such a gene-based condition can survive and perhaps thrive—that culture in some respects buffers the harsh effects of natural selection, and that the former tension due to natural selection has been "relaxed." As populations modernize, the argument goes, the need to personally detect goitrogens and other toxic alkaloids becomes less and less necessary, and—like an unused organ that has atrophied through disuse—the result is a vestige of a former adaptation.
On the other hand, it has been argued that such cultural interventions into "natural" processes, while offering attractive short-term solutions, can ultimately result in a burden. Such ameliorative processes may ultimately only increase the genetic load of populations that exploit strategies that are only beneficial in the short term.
New forms of disease can be inadvertently introduced by iatrogenic measures.13 In some cases, new forms of disease are produced as a direct result of proximate intervention. In the well-known case of phenylke-tonuria, the humane intervention by dietary management has the proximal effect of buffering the naturally debilitating course of this condition during the critical period of post-natal development, but can result in an entirely new form of the disease in subsequent generations, known as maternal phenyketonuria (see Table 1 of the entry Genetic Disease II).
In a more modern—and ethically more complex— case, the cultural response to the genetic disease IDDM was, in the 1920s, due directly to the development of a molecular etiologic model of this mostly genetic disease. This led immediately to substitutional therapy: to the prophylactic substitution of defective human insulin molecules with working analogs of insulin extracted from pigs and cows. These porcine and bovine molecules were used until the 1980s, when less expensive recombinant human insulin produced in transgenic bacteria became available. The proximate, humane result of this medical intervention was that lives were saved, suffering was relieved, and the quality of life for those affected was vastly improved. Furthermore, IDDM individuals who prior to this prophylactic technology would probably have died before reproducing, now survived to procreate, and to achieve fitness parity with the unaffected population. Ironically, to the extent that IDDM (or any disease) is genetic, this meant that affected individuals survived to place new copies of their defective IDDM genes into the next generation, thus potentially increasing the incidence of the disease. Increases in IDDM incidence have been reported in Michigan (1949-1972), France (1988-1995), and in all the Nordic countries, where a secular increase in IDDM incidence has been noted for the past 70 years (Joner & Sovik, 1989; Levy-Marchal, 1998; North et al., 1977).
Under the laws of natural selection, nature is the primary arbiter of life and death. In the case of "relaxed" selection—or what has most recently been called directed evolution—humans have co-opted this role. With our cultural solutions, humans have sometimes become the alternative arbiters of life and death. Formally, directed evolution is a mode of biological selection in which the agent of differential reproduction or differential mortality is a human, or a human-based medical system. The concept is not new. During Darwin's time this process, when applied to plants and animals, was called domestic selection (Darwin, 1868) and was well known to husbandrymen (Russell, 1986).
As a neologism, directed evolution was coined as a supplement to the older term "relaxed selection." Relaxed selection had originally been applied to the cultural buffering of natural selection, but was also a core concept employed by (and therefore negatively associated with) the eugenics movement in pre-World War II America. Today, the term directed evolution has been suggested specifically for cases in which domesticated DNA has been manipulated to serve human ends.14
The "unnatural" cultural modification of a "natural" process may result ultimately in new generations of children born with the gene for IDDM, and such cultural interventions—regardless of the humane motivation for the proximate medical treatment—may increase the incidence of genetic diseases. Proponents of gene therapy hold that humans are now in the early stages of such genetic manipulation, and that the anthropogenic (human-caused) manipulation of genetic diseases can succeed only if followed through to a third logical level of manipulation: gametic gene therapy. But because this third level of gene therapy involves techniques such as embryonic stem cell manipulation and in vitro fertilization, human gametic gene therapy is unlikely to be realized in the current political climate without the advocacy of political lobbyists, genetic counselors, and bioethicists.
Bioethicists are concerned with behaviors and policies concerning biological materials. Issues pertinent to bioethics include organ transplantation, induced abortion and life termination, artificial insemination and sex selection, the use of embryonic tissue in research, and the engineering of genomes. Some of the current bioethical issues are these apparent disparities between the short- and long-term outcomes of medical intervention policies, and costs versus benefits of genetically engineered plants, animals, and humans.
These are complex issues, not only technically, but ethically and morally, as well (see, e.g., Zilinskas & Balint, 2001). In the coming decades, it should be of immense interest to medical anthropologists to follow not only the directed cultural evolution of the new biotechnologies, but also to observe the dynamic of the associated bioethical concerns.
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