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Comment by fragmede | Hacker News Reader

Growing new appendages is clearly much more involved, but a Youtuber was able to give themselves lactose tolerance for a couple of months (they were lactose intolerant before). Assuming it wasn't faked for views, and that we are what we eat, that suggests other modifications to gut bateria aren't inconceivably far off.

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My understanding is that lactose tolerance is a particularly interesting case because lactose tolerance is in fact the mutation and lactose intolerance is the "default". It's just that for historical reasons lactose tolerance obviously conferred an advantage in Europe in particular which is why the mutation persisted. That's why around 40% of the global population are lactose tolerant and intolerance is the global norm.

https://en.wikipedia.org/wiki/Lactase_persistence

If we're thinking about the same youtuber, I found that experimental design to be really poor. They said they were lactose intolerant as a child, but they didn't confirm that they still were (decades?) later. I was lactose intolerant until I was six and then it just resolved on its own (perhaps this wasn't even lactose intolerance but a reaction to something associated with lactose).

What they should have done was eat a pizza before the treatment, gotten sick, then taken the treatment and shown that the same pizza had no effect afterwards.

Considering that there aren’t any mammals that can regrow appendages, chances are adding an appendage would be impossible with gene editing because it would require editing both the mother and offspring to support novel embryonic development.

I seem to think that human children can regrow the tips of their finger if it is cut off (I think the nail is ok, not the joint) though I don't know where I learned that, perhaps a first aid course. I've never tried it though.

That is correct, as long as the injury doesn’t take out the nail bed. That implies that there is some sort of growth factor involved with the nail bed as a signaling center, but regrown finger tips are a very simple case compared to actual appendages.

Finger tips are mostly fatty soft tissue minus the muscle, which is known to regenerate. Stuff like nerves are a completely different issue and children who regrow finger tips usually lose finer sensory input like two point discrimination.

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