> The approach may work a while. But then I am sure some mutant gene will eventually emerge in the wild-type populations that will inhibit the synthetic kill gene.

> That's how Nature works.

More accurately, "That's how Nature works, sometimes."

The statement "...some mutant gene will eventually emerge ... that will inhibit [another gene]" describes one subset of the set of all possible causes of future genetic expression branching from this point. There is no law (that we are yet aware of) that allows us to say conclusively that a certain genetic trait will be selected for or against with any meaningful certainty. Furthermore, we have no scientific footing on which to say 'we are sure that a specific mutation will arise that will inhibit this other mutation' as decreed by Nature. In order for the claim to always be true in all arbitrary subsets of Nature, we would need to at least know: whether or not the gene will be selected against, specifically how the gene will be selected against, and nearly all nth order organism-local and population-global effects of a specific mutation or selection event. (We can play Nature in the lab and make approximations of the claim, though! Sort of.)

We can make statements like "If the oxygen content of that atmosphere or environment increases, it is possible that many anaerobic organisms will be selected against." Or, "If low hemoglobin production becomes advantageous, at some point after that, conditions x, y, and ... will likely exhibit reciprocal selective pressures."

Of course, we can also say things like, "All species are statistically likely to go extinct." (That's not very interesting.)

Essentially, we can make broad guesses about future states of genetic expression (and implied warranties and effects) under certain specific contexts. But we cannot say that a specific genetic cause and effect will occur as derived from an inherent property of Nature and a specific sub-state of the universe. As far as we know, genetics, mutation, evolution, and selection are just functions in a mostly random, iterated chaotic system that we are just beginning to comprehend.

We cannot say that 'a particular gene will be selected against, because it is inevitable that specific genes are invariably inhibited or selected against by subsequent shifts in population genetics.' In a sense, that's partially accurate. All species, and by extension, each gene and all genomes, are likely to be selected against. But not always via mutation. It's about the same as saying that species go extinct because of x; it's not certain to be true and may not yield any new information.

There is no law (that we know of) that allows us to make deterministic statements like 'X% of the genome will be inhibited because of the emergence of another mutation'.

For all we know, a rogue asteroid might hit Earth on Tuesday during rush hour in Hong Kong. Or, that particular gene may end up surviving until the closest possible moment before the heat death of the universe. On a more fundamental level, we'd need laws that allow us to predict specific future events (with interesting and meaningful degrees of certainty). We would need to be able to identify and map the exquisitely threaded chaos woven throughout Nature before we can be reasonably certain that 'a mutation will eventually arise to inhibit this other mutation.'