Sean Carroll

In natural selection or biology, it's exactly the same thing.

You can see the animal, but you can't, by looking at the animal, read all of its DNA sequence, and therefore you can only make probabilistic statements about will the baby be a boy or a girl, right?

So it's very, very easy for there to be fundamentally different kinds of behavior at a macroscopic level than at a microscopic level.

Okay.

So I think that answers all the general questions.

Let me go through very, very quickly here.

Dan R. says, a complex system is still entirely constrained by the deterministic laws of its basic part.

Sure, it is.

But you don't know the state of the basic parts.

And it's not just you happen not to know.

They are literally unavailable to you at that macroscopic level.

In some sense, at the microscopic level, it is entirely valid to say that that intent that you had at the macro level came from an unchosen lottery of genes, hormones, and prior environment.

So what?

You don't know.

It's not part of that macro theory.

The macro theory is one in which people are not predictable and make choices.

And that's just how the macro theory goes.

To Ian's question, I think that was very close to the way that I answered already.

But he says, if fundamental physics equals deterministic and my brain equals fundamental physics, how can we say my brain is not deterministic?

The answer is your brain is not fundamental physics.