Retina is a good example of this. Zebrafish can regrow damaged retina, but while mammals have the same stem cells (Muller glia), they dont repair the retina, but form scar tissue. There is a lot of research and I think they have managed to modify rat genome, so that their retina has showns some repair abilities. The problem is that it often causes tumors.

I have other retina permanently damaged, and suffer from double vision when looking small objects like text.

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cortesoft 3 hours ago | parent [-]

Ah, I was wondering the evolutionary reason why those genes would have gone dormant.

Cancer is a sensible answer.

	▲	Sharlin 3 hours ago \| parent \| next [-]
		Yep, the unfortunate flipside of "let's use stem cells to rebuild stuff" is always "let's use stem cells to give us cancer". Technology might help alleviate the cancer part compared to blind evolution, hopefully.
	▲	themafia 18 minutes ago \| parent \| prev \| next [-]
		Teratomas are insane. https://en.wikipedia.org/wiki/Teratoma
	▲	api 2 hours ago \| parent \| prev [-]
		Some aging mechanisms like telomeres are also mechanisms to prevent cancer by limiting cell division. It looks like one of the optimization edges walked by evolution is a conflict between longevity and the ability to repair and regenerate versus not getting cancer. It’s easy to make human cell lines immortal, but that will kill you. One route I can imagine to radical life extension is to start by editing the genome to introduce much more robust but different anti cancer adaptations. Then start turning regenerative stuff and things like telomerase back on.