[Ichneumon]

I would be a bit sceptical. It turns out that humans were "supposed" to make N-Glycolylneuraminic acid but the corresponding enzyme gene got damaged somewhere along the way.

Exactly the same is true of Vitamin-C (all mammals except for guinea pigs and primates -- which includes humans -- produce their own Vitamin-C internally), but you don't see articles claiming, "Vitamin molecule may cause health problems". On the contrary, we *need* the Vitamin-C we get from external food sources, and *avoiding* eating foods which contain Vitamin-C is what actually causes "health problems" like the disease Rickets.

If fact, it was only because Vitamin-C was present in sufficient amounts in primates' diets that the mutation which "broke" our Vitamin-C synthesis gene wasn't immediately weeded out by natural selection. I suspect the same may be true of the "broken" human N-Glycolylneuraminic acid synthesis gene.

[facedown]

I suspect the same may be true of the "broken" human N-Glycolylneuraminic acid synthesis gene.

I don't know if N-Gn is an essential nutritional like vitamin C but but if so carnivorous primates would survive.

[Smokin' Joe]

...*avoiding* eating foods which contain Vitamin-C is what actually causes "health problems" like the disease Rickets.

I think the one you are looking for is "Scurvy". IIRC, I think Rickets is Vit. D defeciency related.