> This argument depends on whether there is a 'natural' biochemical scaffolding for life that resembles what we have on Earth. I don't think the argument hinge

> This argument depends on whether there is a 'natural' biochemical scaffolding for life that resembles what we have on Earth. I don't think the argument hinges on a notion of 'naturality'. Instead it seems to be more of an statistical/occams razor kind of argument: Mixed chiralities would introduce a lot of incompatabilities among the building blocks, making the emergence of a stable form/process more unlikely. And also the argument (as far as I understand it) is in no contradiction to your caveat: Of course, a stable form/process might have emerged with mixed chirality. But it did not and was never very likely to begin with. [Note: This is not a statement about assigning truth values to these arguments but rather I hope it clearifies the argument itself.]