The prevailing wisdom has, for a long time, been that having a giant planet like Jupiter in a solar system is a good thing for the evolution of life. Smaller planets like our own are, the story goes, protected by the gravitational vacuuming power of a big gas giant. Lots of comets, asteroids and other potential collisional threats get sucked in by Jupiter gravity field. This allows life on smaller worlds a better chance of making some progress before getting sterilized by an impact.
Now new research is challenging that story. Over at Centauri Dreams you can find a nice discussion of new work by Jonathan Horner (University of New South Wales) and Barrie Jones (The Open University, UK). Their study implies gas giants might not be so helpful. Looking at impact scearios under different conditions their simulations imply that collision rates can, in some cases, go up with a larger planet in a solar system. The authors of the study conclude,
"As such, it seems that Jupiter can easily be at least as much, if not more, of a foe than it is a friend."
We are just at the beginning of this game of understanding how solar system architecture effects the chances for life (and complex life at that) developing. Part of this process will naturally involve having old assumptions challenged and, perhaps, overturned.