Humans do not naturally produce Neu5GC, a sialic acid that was lost during human evolution, potentially as a defense against malaria.

“Humans don't make new5GC. There's an enzyme that does make new5GC that was lost in our history and part of the hypothesis around this is that earlier versions of malaria used new5GC or may have used new5GC to enter cells. Thus, by losing new5GC on the surface of our cells, we may have been able to escape that malaria pandemic, epidemic, etc.”