So our biologists Ursula and Stuart have been carrying on a very cool discussion about emergence and reductionism. This may seem a tad academic to some but it is actually at the heart of the culture of science, especially as it relates to how science has driven culture as a whole.
For right now I thought I would just try and fix the question a bit more firmly from the physicists' perspective.
For the last 5 decades we physicists have dreamed a little dream called the TOE - the Theory of Everything. Briefly put, the dream went like this - once you have this TOE you are done. You know everything there is to know in principle. This theory will be simple, and elegant. It will be so simple and elegant, that it should be expressible via an equation that fits on a T-shirt (the kind you proudly wear at the next Omni-Universe-Sci-Fi-Convention).
Now this theory may turn out to be something like String Theory or it may turn out to be something entirely different. Whatever it is, it will rule and we will all be happy. We will understand how all the forces governing all the different kinds of stuff in the Universe came about. In fact we will understand much of how the Universe as a whole came about.
Now the next question is simple - is that enough?
Would that be all I need - in principle - to understand the entire history of history? Would that be all I need to understand - to predict -- all the structures that that we see around us.
Of course there are many caveats that should be added to my formulation of the question, most importantly the role of quantum mechanics and its fundamental addition of probabilities. Still, the idea that a theory describing the most fundamental level of reality (particles or strings or whatever) is all that you need, in principle, to describe the higher levels (planets and people and puma's) still holds a lot of currency in the halls I walk.
There will be more on this from all of us - including why so much of western thinking about science and culture does or does not hinge on this question - but for now I wanted to be very clear about what I think we are arguing about.