A thought about individual selection

I recently conversed with a friend about Darwin and amenorrhea, which led to my new experience and appreciation for this thought: In amenorrhea, there is no normal menstrual flow in a female of reproductive age. One interesting finding is that as the female body ceases producing eggs, it then actually channels energy to sustain the body. To me, this suggests that instead of trying to pass on individual genes by reproducing, the metabolic process concentrates on individual rather than species survival. Amenorrhea usually occurs in emaciated, malnourished females experiencing starvation. The condition of amenorrhea could then allow females to survive the starvation period by essentially shutting off reproductive potential and maintaining self-sustenance. One consequence would be that the females' reproductive organs could be permanently damaged. Then, they would not be able to reproduce. Or, another consequence could be that the females segway directly into menopause and lose reproductive capacity altogether. Amenorrhea thus seems to be an exception to Darwin's typically understood theory that evolution favors survival of the species over the individual. Yes, he has proposed that the fittest individuals survive, but usually, the associated biological mechanisms seem to support individual sacrifice for the sake of progeny survival (take for example maternal grandmother lionesses that will fight to the death an intruding male lion that will commit infanticide on the previous male lion's offspring). So is it possible to conceive then, that Darwin's principles apply on an individual level more than previously envisioned? Is "species" just a mental construct?
-Bonnie Chien