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Humans Might Be So Sickly Because We Evolved to Avoid a Single Devastating Disease:
Sialic acids are a diverse group of carbohydrates that blossom like leaves from the tips of proteins covering the surfaces of human cells.
[...] Changes in sialic acid markers can give rise to a number of diseases. But it was one specific change particular to all humans that the researchers here were most keen to gain an understanding of.
Most mammals – including closely related apes – have a compound called N-glycolylneuraminic acid, or Neu5Gc. We've known for some time that the gene for this version of sialic acid is broken in us, leaving its precursor form, N-acetylneuraminic acid (Neu5Ac), to do its job.
Researchers previously speculated that this mutation was selected for in humans to make it harder for devastating malarial parasites such as Plasmodium knowlesi to latch onto red blood cells.
[...] Since chimpanzees retain the gene for Neu5Gc, the mutation must have occurred within the past 6 million years or so, sometime after we parted ways from one another.
[...] This most recent study shows Neanderthals and Denisovans share our variant of sialic acid, meaning the change happened before our branch of the family tree separated roughly 400,000 to 800,000 years ago.
[...] To differentiate between cells that belong to us from possible invaders, our immune cells are armed with a scanning chemical called sialic acid-binding immunoglobulin-type lectins. Or Siglecs for short.
When an inspection occurs, if a cell's sialic acid marker isn't up to scratch, it's curtains for that cell. Naturally, any changes to our sialic acid name-tag would imply our system of Siglecs would have needed adjusting as well.
Sure enough, on further investigation the researchers found significant mutations among a cluster of Siglec genes that are common to humans and their ilk, but not great apes.
[...] Siglec expression is linked with conditions such as asthma and Alzheimer's disease, raising the possibility that protection from a devastating disease put us at risk of other conditions.
Journal Reference:
Naazneen Khan, Marc de Manuel, Stephane Peyregne, et al. Multiple Genomic Events Altering Hominin SIGLEC Biology and Innate Immunity Predated the Common Ancestor of Humans and Archaic Hominins [open], Genome Biology and Evolution (DOI: 10.1093/gbe/evaa125)
(Score: 1, Interesting) by Anonymous Coward on Monday August 10 2020, @01:20PM
I think there are arguments to be made on both sides.
For example most bacteria that switch on their antibiotic resistance traits will often eventually revert back to their prior states if the antibiotic is removed from the environment. While the bacteria can make adaptations to fight the antibiotic the cost of those adaptations make them undesirable if the antibiotic is absent in the environment.
Likewise we have an immune system with various functions and adaptations. But those adaptations aren't free, they come at a cost.
An obvious example could be sickle cell anemia and malaria. Having sickle cells isn't necessarily a good thing. But if you are heterozygous the cost to you is minimal (though there is still a small cost to you directly there is a potentially much larger cost to your offspring) but the benefits to you of being resistant to malaria outweigh the cost if you live in an environment riddled with malaria. If malaria doesn't exist you and especially your offspring are much better off not having the sickle cell gene whatsoever.