Some opponents of Warren's view believe that what matters morally is not that one be "actually exhibiting" complex mental qualities of the sort she identifies, but rather that one have in oneself a self-directed genetic propensity or natural capacity to develop such qualities. In other words, what is crucial is that one be the "kind" of entity or substance that, under the right conditions, actively develops itself to the point of exhibiting Warren's qualities at some point in its life, even if it does not "actually" exhibit them because of not having developed them yet (embryo, infant) or having lost them (severe Alzheimer's). Because human beings do have this natural capacity—and indeed have it "essentially"—therefore (on this view) they "essentially" have a right to life: they could not possibly "fail" to have a right to life. Further, since modern embryology shows that the embryo begins to exist at conception and has a natural capacity for complex mental qualities, therefore the right to life begins at conception.