View Full Version : Big brains=prone to cancer but longer lives?

Little bit
10-15-2012, 02:12 PM
Humans evolution towards bigger brains may come at the cost of being more prone to cancer due to reduced apoptosis:

There's a downside to everything. When humans evolved bigger brains, we became the smartest animal alive and were able to colonise the entire planet. But for our minds to expand, a new theory goes, our cells had to become less willing to commit suicide and that may have made us more prone to cancer.

When cells become damaged or just aren't needed, they self-destruct in a process called apoptosis. In developing organisms, apoptosis is just as important as cell growth for generating organs and appendages it helps "prune" structures to their final form.

By getting rid of malfunctioning cells, apoptosis also prevents cells from growing into tumours. "Reduced apoptotic function is well known to be associated with cancer onset," says John McDonald of the Georgia Institute of Technology in Atlanta.

It makes me wonder if autism, known for big brains with excess neurons early on, could be a mistake or even just "growing pains" of this process. The theory is that genes promoting apoptosis are down-regulated in humans, and those turning apoptosis off are up-regulated. We see similar quirks in gene regulation in autism as well. The upside of this reduced apoptosis is longevity:

Preuss says that lower levels of apoptosis could also help explain why humans live so much longer than other primates, something that allows us to lavish time on raising children and acquiring knowledge. "Animals with larger brains tend to live longer," he says.

Little bit
10-15-2012, 02:24 PM
Btw, a snp of the TP53 gene has been cited for apoptosis:

Rs1042522 C or G - dbSNP Orientation is Minus, so 23andme customers should flip their results C=G and G=C.

For example, I am CC at 23andme, and would therefore be GG for interpreting my results. Too bad, CC's live 3 years longer than GG's, thanks to increases apoptosis>:(

[PMID 18256523] Minor allele homozygotes, i.e. rs1042522(C;C) genotypes, live on average 3 years longer than major allele (G;G) homozygotes, based on a study of 9,200+ Danish individuals. The increased longevity is speculated to be related to the increased apoptosis seen for this gain of function SNP, presumably due to "increased robustness" during the period of treatment after the diagnosis of life-threatening diseases such as cancer of certain types.

10-16-2012, 11:49 PM
Very interesting theory. Unfortunately, we don't know enough to properly evaluate it. I'd also be hesitant to start applying it to pathology, much less such a poorly-understood disorder as autism.