Читать книгу Bioethics - Группа авторов - Страница 114

There is one doubt about the workability of schemes of genetic improvement which is so widespread that it would be perverse to ignore it. This is the view that, in any genetic alteration, there are no gains without compensating losses. On this view, if we bring about a genetically based improvement, such as higher intelligence, we are bound to pay a price somewhere else: perhaps the more intelligent people will have less resistance to disease, or will be less physically agile. If correct, this might so undermine the practicability of applying eugenics or genetic engineering that it would be hardly worth discussing the values involved in such programmes.

This view perhaps depends on some idea that natural selection is so efficient that, in terms of gene survival, we must already be as efficient as it is possible to be. If it were possible to push up intelligence without weakening some other part of the system, natural selection would already have done so. But this is a naive version of evolutionary theory. In real evolutionary theory, far from the genetic status quo always being the best possible for a given environment, some mutations turn out to be advantageous, and this is the origin of evolutionary progress. If natural mutations can be beneficial without a compensating loss, why should artificially induced ones not be so too?

It should also be noticed that there are two different ideas of what counts as a gain or a loss. From the point of view of evolutionary progress, gains and losses are simply advantages and disadvantages from the point of view of gene survival. But we are not compelled to take this view. If we could engineer a genetic change in some people which would have the effect of making them musical prodigies but also sterile, this would be a hopeless gene in terms of survival, but this need not force us, or the musical prodigies themselves, to think of the change as for the worse. It depends on how we rate musical ability as against having children, and evolutionary survival does not dictate priorities here.

The view that gains and losses are tied up with each other need not depend on the dogma that natural selection must have created the best of all possible sets of genes. A more cautiously empirical version of the claim says there is a tendency for gains to be accompanied by losses. John Maynard Smith, in his paper on ‘Eugenics and Utopia’,⁶ takes this kind of ‘broad balance’ view and runs it the other way, suggesting, as an argument in defence of medicine, that any loss of genetic resistance to disease is likely to be a good thing: ‘The reason for this is that in evolution, as in other fields, one seldom gets something for nothing. Genes which confer disease‐resistance are likely to have harmful effects in other ways: this is certainly true of the gene for sickle‐cell anaemia and may be a general rule. If so, absence of selection in favour of disease resistance may be eugenic.’

It is important that different characteristics may turn out to be genetically linked in ways we do not yet realize. In our present state of knowledge, engineering for some improvement might easily bring some unpredicted but genetically linked disadvantage. But we do not have to accept that there will in general be a broad balance, so that there is a presumption that any gain will be accompanied by a compensating loss (or Maynard Smith’s version that we can expect a compensating gain for any loss). The reason is that what counts as a gain or loss varies in different contexts. Take Maynard Smith’s example of sickle‐cell anaemia. The reason why sickle‐cell anaemia is widespread in Africa is that it is genetically linked with resistance to malaria. Those who are heterozygous (who inherit one sickle‐cell gene and one normal gene) are resistant to malaria, while those who are homozygous (whose genes are both sickle‐cell) get sickle‐cell anaemia. If we use genetic engineering to knock out sickle‐cell anaemia where malaria is common, we will pay the price of having more malaria. But when we eradicate malaria, the gain will not involve this loss. Because losses are relative to context, any generalization about the impossibility of overall improvements is dubious.