It should be remembered that the boundary, though it is measured by which individuals survive long enough to contribute to future genetic distributions, is not primarily dependent on any particular population. The boundary is determined by the characteristics of the environment the population finds itself in.

If we are talking about Arctic hares, the boundary might be the degree of pigment that can be tolerated in the white winter fur before the hare becomes too easily found by a predator. The boundary is a characteristic of the environment, even if it may be measured in terms of the characteristics of the animal.

Without bothering with "the fittest", we can state without contradiction that the "unfit", who are those just outside the boundary, do not "survive", using "survive" in the sense of making a significant contribution to future gene pools. Thus it is clear that the undisputed fundamental rule of evolutionary dynamics is "The Non-survival of the Unfit".

It seems reasonable that this was also evident to Darwin and Spencer, but they wanted a more positive statement. They just fell into the logical trap of thinking that the positive equivalent of "Nonsurvival of the Unfit" was "Survival of the Fittest". Figure EG0506b shows that this simply isn't the case.

But it would be nice to be able to make the statement of the basic principle of evolution take a more positive form by emphasizing those who do survive. We can do that by looking at the boundary again. We see that the individuals who survive are those inside the boundary.

Since the individuals at the boundary are the ones who just barely manage to survive, the population we are looking for contains those who are at least that fit. Thus the positive equivalent of "The Non-survival of the Unfit" can be stated as "The Survival of the Just-Barely-Fit-or-Fitter".

Since the boundary cases are the defining ones we can simplify this to "The Survival of the Just-Barely-Fit".

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