Mutation and Human Exceptionalism: Our Future Genetic Load
GENETICS March 7, 2016 vol. 202 no. 3 869-875; DOI: 10.1534/genetics.115.180471
Although the human germline mutation rate is higher than that in any other well-studied species, the rate is not exceptional once the effective genome size and effective population size are taken into consideration. Human somatic mutation rates are substantially elevated above those in the germline, but this is also seen in other species. What is exceptional about humans is the recent detachment from the challenges of the natural environment and the ability to modify phenotypic traits in ways that mitigate the fitness effects of mutations, e.g., precision and personalized medicine. This results in a relaxation of selection against mildly deleterious mutations, including those magnifying the mutation rate itself. The long-term consequence of such effects is an expected genetic deterioration in the baseline human condition, potentially measurable on the timescale of a few generations in westernized societies, and because the brain is a particularly large mutational target, this is of particular concern. Ultimately, the price will have to be covered by further investment in various forms of medical intervention. Resolving the uncertainties of the magnitude and timescale of these effects will require the establishment of stable, standardized, multigenerational measurement procedures for various human traits.
… Taking the lower end of the latter range suggests that the recurrent load of mutations imposed on the human population drags fitness down per generation …
Summing up to this point, our current knowledge of the rate and likely effects of mutation in humans suggests a 1% or so decline in the baseline performance of physical and mental attributes in populations with the resources and inclination toward minimizing the fitness consequences of mutations with minor effects.
A fitness decline of a few percent on the timescale of a century is on the order of the rate of global warming, and that is part of the problem. What will it take to promote serious discourse on the slowly emerging, long-term negative consequences of policies jointly promoted by political, social, and religious factors? Should such a discussion even be pursued or should the process of accelerated genetic change simply be allowed to run its course—a slow walk down the path to what Hamilton (2001) called “the great Planetary Hospital”? Unlike global environmental change, there is no obvious technological fix for the uniquely human goal of intentionally ameliorating the effects of mutation, nor is there a simple ethical imperative for doing otherwise, short of refocusing our ethical goals on future descendants.
This is the kind of dysgenic logic that worried people like the great William D. Hamilton (a lot, in Hamilton’s case, due to personal reasons besides the Darwinian cultural heritage — he grew up five miles from Darwin’s home). Note that it’s a different cause for dysgenic worry than the differential rate of breeding worry featured in Idiocracy.
On the other hand, doot-dee-doot-dee-doo, I’m not all that worried.
First, I don’t know for sure that it’s really happening.
Second, the persuasiveness of dysgenic logic is one reason why people kept discovering the Flynn Effect and then losing it (until James Flynn made sure that after him it would stay discovered).
Third, I would assume that while the advent of practical genetic engineering for humans isn’t going to happen as fast as I figured it would back in 1999, it will likely still happen within a few generations. So, that looks like a solution that will likely kick in before things get too bad.
On the other hand, fifty years ago everybody assumed that the problems caused by fossil fuel use would soon be gone because nuclear power is only going to get ever more cost-effective. (Not to mention that fusion power would be here Real Soon Now.) Last summer, however, I went for a memorable walk along the base of the recently shuttered San Onofre nuclear power plant.
So, what do I know about the future?