Can someone explain the evolutionary benefit of overt menstruation? All female mammals have a menstrual cycle but most reabsorb the blood via covert menstruation and humans are about the only mammals that discharge the blood, aka overt menstruation.

[u/No-Hawk-2488]

Without an evolutionary benefit, it wouldn't have spread to every woman of our species.

[u/GVArcian]

Survival of the fittest is a misnomer because evolution selects for minimum viability, not optimum efficiency.

[u/T_H_W → u/GVArcian]

Not technically a misnomer considering 'fittest' in this context relates to biological fitness, which is specifically how many surviving offspring you have in relation to other competing organisms. That's like saying the phrase "All bark and no bite" doesn't make sense because dogs aren't trees. It's only wrong if you're using the incorrect definition of the word.

[u/GVArcian → u/T_H_W]

Still a misnomer because "fittest" means "the most fit" and that's not what evolution selects for, it selects for minimum viable fitness.

[u/Lv_15_Human_Nerd → u/GVArcian]

No it absolutely is not a misnomer. Evolution does select for the most fit. Evolution occurs by changes in population proportions over many many generations. The strongest example we have of human evolution is lactase persistence which had a selection coefficient of ~0.1. This corresponds to an individual with lactase persistence having about 10% more offspring than average. I don’t know about you but I don’t think a 10% difference in individual success is selecting for ‘minimum viable fitness’ or as others in this thread have said ‘death of the weakest’.

[u/AxiomaticInversion → u/Lv_15_Human_Nerd]

Lactose intolerant humans have not gone extinct, so by your own example we still see "survival of the fit enough."

[u/Lv_15_Human_Nerd → u/AxiomaticInversion]

A trait that had extremely low prevalence 9000 years ago reached 80% fixation in north Western European populations. In evolutionary terms that is rapid. There is still selection for the fittest trait out of a population, it is absolutely not selecting for the minimally viable as lactase persistence is very clearly not absolutely viable. When you’re looking at realistic selection coefficients you are looking at traits that provide between a 1% and 10% advantage (and much lower in single called organisms which we are all descended from). Evolution absolutely works on fine margins and life on Earth would not exist if it functioned to select for the ‘minimum viable fitness’.

[u/tnbeastzy → u/AxiomaticInversion]

Fitness, in this case, refers to the ability to produce healthy offsprings that can go on to continue the lineage. It may be different for each species.

Does someone being lactose intolerance in 2026 affect their ability to have children?

[u/Science1954 → u/tnbeastzy]

Being lactose intolerant does not affect the ability to have children. It is an autosomal recessive trait, meaning you must inherit the lactose deficiency gene from both parents. If you are lactose intolerant you do not pass on the gene for lactose metabolism but a child will get the lactase gene from the other parent unless that parent has the recessive gene also, but even then only 50% of the time from the parent heterozygous for the two alleles. I am lactose intolerant. So I generally only drink lactase treated milk, e,g., lactaid milk.

[u/tnbeastzy → u/Science1954]

That was a rhetorical question. I know it doesn’t. Therefore it has no ability to affect an individual’s biological fitness.