Michael Levin

How do you control all the individual low-level rules, right, all the protein interactions and everything else?

Rolling it back from the anatomy that you want to the low-level hardware rules is, in general, intractable.

It's an inverse problem that's generally not solvable.

So right now it's mostly in the lab because what we need to do is we need to understand how biology uses top-down controls.

So the idea is not bottom-up emergence, but the idea of things like goal-directed test-operate-exit kinds of loops, where it's basically an error minimization function over a new space.

It's not a space of gene expression, but for example, a space of anatomy.

So just as a simple example, if you have a salamander and it's got an arm, you can amputate that arm anywhere along the length.

It will grow exactly what's needed and then it stops.

That's the most amazing thing about regeneration is that it stops.

It knows when to stop.

When does it stop?

It stops when a correct salamander arm has been completed.

So that tells you that's right.

That's a...

A means ends kind of analysis where it has to know what the correct limb is supposed to look like, right?

So it has a way to ascertain the current shape.

It has a way to measure that delta from what shape it's supposed to be.

And then it will keep taking actions, meaning remodeling and growing and everything else until that's complete.

So once you know that, and we've taken advantage of this in the lab to do some really wild things with both planaria and frog embryos and so on.

Once you know that, you can start playing with that homeostatic cycle.