What plays a more important role in dog behaviour - nature or nurture?

My answer would be 'both', although nurture to a greater extent in most cases. I do believe that certain behavioural traits are genetic, but I also believe that behaviours are moulded throughout a dog's life.

There's also a 'Chicken or the egg' problem of sorts, though. Scenario:

A bitch is dog aggressive and has a litter of pups. All of these pups are sent to good homes with good owners, and yet they all become dog aggressive. Is this because of a genetic link or did the behaviour develop after birth through imitation of the bitch?

Now you could reason that it would depend on when the aggressive behaviour showed itself and that, if it was after the pups reached maturity, nature was to blame. What do you think?

I've voted Nature. Of course Nurture has a huge role to play, but I would never get a pup if I knew one or the other parent (but particularly the mum) was aggressive.

Nor would I! I'd always ask to see at least the dam. The sire too, if possible. If one was aggressive, I'd want to know exactly why and to what extent.

I said both. I am terrible at trying to explain what I mean but I think that nurture can play a huge role in shaping a dogs behaviour but you are working with the basics that nature has already put there.

Actually, I think that was really well said! Something I hadn't really thought of before.