Life is not improbable.

[Chas]

Really? Is there such a thing as a priori probability being 1?

I'm using a definition for evolution here which is rather loose or broad......Basically I am thinking that evolution is just descent with change.

But you are correct, it isn't 1 because over any time specified time scale I suppose there is a probability that life as we know it can occur were there is descent but no change.

Thanks for prompting the thought.

But evolution is not 'just descent with change'. You've left out the critical ingredient - selection.