Will aliens look like us? Answer involves ergodicity & predictability of evolution

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EXCERPTS: The aliens you see in science fiction movies and TV often look a lot like us [...] If Darwinian evolution works on other planets, will they lead to forms of life — literally how it appears — like we find on Earth?

In our own planet’s history, for example, we do see different versions of wings evolving on many separate occasions in many separate species. This is convergent evolution, and if we knew it always happened, then we could say that evolution is, in some sense, predictable. In that case we could tell if and when aliens would look like us.

But there is a long and fierce tradition of argumentation about convergent evolution. Today, I want to unpack one line in this fight which is new (to me at least) and touches on one of the deepest issues not in biology but in physics: a crazy, profound idea called ergodicity.

[...] Now let’s make the jump to biology. Here is the killer question: Is evolution ergodic? Like statistical mechanics, evolution links the random microscopic world (gene mutations) with the macroscopic world (the shape and function of living things). If evolution is ergodic — that is, if the trajectory of the evolution of a species behaved in its “phase space” of possibilities the way molecules in a coffee cup do — then we might be able to predict evolutionary outcomes. We could know in advance what evolution would lead to. We even might be able to tell that, in principle if not in practice, circumstances on exoplanet XB4-27A will lead to humanoid looking creatures (but with pointy ears of course).

So, is evolution ergodic? Will it explore all its crazy hyperdimensional phase space?

[...] As of now, there is no answer to this question of evolution and ergodicity. I suspect that if you polled biologists, most would tend to argue against ergodicity. The thing I wanted to call out here though — the thing that is really super cool — is how the argument itself works. Evolution’s predictability, which is a huge question, gets mapped onto the properties of a crazy, hyper-abstract, hyperdimensional space of possibilities. The fact that this is even conceptually possible is what makes my head swim with wonder. It might even be cooler, or at least just as cool, as knowing if aliens will look like us... (MORE - missing details)

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