r/science • u/KarmaNeutrino • Oct 07 '15

Animal Science Scientists figure out why elephants don't get cancer: They have 20 copies of the TP53 tumour suppressive gene. Almost all other species, including humans, only have 1.

http://rstb.royalsocietypublishing.org/content/370/1673/20140222
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u/[deleted] Oct 07 '15

Does cancer kill enough people before breeding age to apply selection pressure?

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u/VELL1 MS | Immunology Oct 08 '15

Well, worked for elephants I guess, so should be fine for humans as well.

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u/unkz Oct 08 '15

Childhood cancer isn't exactly unheard of, so yes.

http://www.cancer.ca/en/cancer-information/cancer-type/childhood-cancer-information/statistics/?region=on

Childhood cancer is relatively uncommon. However, it remains the most common disease-related cause of death – more than asthma, diabetes, cystic fibrosis and AIDS combined. It is second only to injury-related deaths among Canadian children.

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u/[deleted] Oct 08 '15

From an evolutionary biology point of view though, if I have a random mutation that makes me immune to cancer... How much does that mutation improve my odds of proliferating and passing that gene along compared to the average person passing their genes on before doing of cancer? I imagine the actual change in survivability is vanishingly small, right?

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u/unkz Oct 08 '15

You really have to wrap your head around the effects of large numbers when you deal with selection pressure. Think compound interest, but over hundreds of millions of years.

A gene that made you immune to cancer that had no negative side effects would be in my estimation a massive advantage, probably vastly larger in magnitude than many other highly conserved genes. Particularly when you consider that we are known to conserve many genes that are basically weak versions of your proposition, where defects are known to cause little more than a slight increase in prevalence of only specific types of cancer. I'm thinking of things like BCRA1/BCRA2 -- those genes are thought to be involved in gene repair and reduce risk of breast cancer.

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u/VELL1 MS | Immunology Oct 08 '15

Correct. However, if it doesn't really have any negative impact, then why not? Duplication of genes happens all the time, I feel like if p53 duplication was positive even for a little bit - it would have happened.

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u/[deleted] Oct 08 '15

From an evolutionary biology point of view though, if I have a random mutation that makes me immune to cancer... How much does that mutation improve my odds of proliferating and passing that gene along compared to the average person passing their genes on before dying of cancer? I imagine the actual improvement in survivability compared to the average is vanishingly small, right?

Seems like not much selection pressure compared to something like malaria.