@Setanta,
There are several toy level (and a number of research level) programs that parallel the development on this planet and use it as inputs to see what could happen if certain conditions change through history.
All of these runs require some rather simple changes in the earths (or any planets ) initial environments to promote the development of a loooong period of single to multicell life.Whats kind of neat is that The occurrence of a Cambrian Explosion is almost a chemical" given" as free Carbonate and a buffered saline environment occur.
These chemical conditions are apparently driven to occur as long as the planet has a molten and multi-layer mantle (so that continents can drift about and erode salts) and the planet contains free water. It concludes that a Cambrian Explosion style of a blooming life is sorta inevitable (based upon the inputs on the models).
AFTER a Cambrian Explosion however, its a Chinese fire drill. In most all cases, life adapted to an environment and there was no innate driving of life to become "clever" . So, using biological expansions, the chances of developing a big brained pinnacle species who controls his environment is about 99% staked against.99% is good enough to say its inevitable that some time a clever pinnacle species would develop(maybe itd be a lizard or even some other new form of life that isn't anything like we can recognize)
SO, according to that, the only variable that deteremines the inevitability of anything is time and the good luck not to be wiped out by a bolide,solar flare, or gamma burst in the neighborhood.
I think we will ultimately extend our influence to a coupleof lightyears out there. So all these things will be be made obvious to us. I just wish I could live longer and see it happen.
outcomes.