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"A primary cause of somatic mutations has to do with errors during the DNA replication that occurs when cells divide—neural progenitor cells undergo tens of bil
by reubenswartz 9y ago
"A primary cause of somatic mutations has to do with errors during the DNA replication that occurs when cells divide—neural progenitor cells undergo tens of billions of cell divisions during brain development, proliferating rapidly to produce the 80 billion neurons in a mature brain."
Certainly there must be tens of billions of cell divisions to create all the neurons, but each neural progenitor cell would only divide 30-40 times, right?
I'm not surprised that there are mutations, but the number of mutations is remarkable to me, and seems like yet another evolutionary check on brain size that I hadn't considered (energy use, difficulty of birth, and difficulty of childhood being the more obvious ones).
- nonbel 9y ago>"Certainly there must be tens of billions of cell divisions to create all the neurons, but each neural progenitor cell would only divide 30-40 times, right?" Surprisingly to most, this is not a mainstream opinion: https://www.ncbi.nlm.nih.gov/pubmed/25459141 https://www.ncbi.nlm.nih.gov/pubmed/25459141 I would guess the main reason is that it leads to major problems with the current model of cancer.
- reubenswartz 9y agoThanks for the link. Very interesting stuff. Also worth noting that there's a difference between mutation and cancer, although of course they're related. Just as mice and people get cancer at similar rates, so do elephants, which have many more cell divisions, but have more elaborate anticancer mechanisms (presumably because elephants lacking them died of cancer).
- nonbel 9y agoIf you give humans 2^53 divisions (as in that paper) and elephants have ~100x the mass of humans, as a rough estimate they would require 2^60 divisions. So about 7 more divisions per stem cell to live as long as the usual human (they usually don't live that long).
- nonbel 9y agoInstead of "per stem cell" that should be 7 more divisions from the zygote.
- reubenswartz 9y agoFor some of the cells, like neurons, that to a first approximation don't divide in adulthood, this seems true. But for things like blood cells that are constantly getting turned over, it seems like there would be a lot more opportunities for bad mutations in a larger creature (although as your link suggests, there seems to be some fairly strong defense against this).