There are a couple of posts my fellow dog-bloggers submitted that caught my eye.
One was about "Cujo", the runaway and intimidating German Shepherd and specifically the comment that two people were killed by dogs in the author's county; the other one about the life guard stray dog in India.

After reading both posts the question "How come that some dogs are great while others are killers" came to my mind. A question that frequently pops up and a thought I have pondered over for quite some time.

Aside from physical reasons that explain attacks, what causes a stray dog to safe people's lives on a beach in India, while others in the same country are mass culled because they attack humans? Why do some strays become excellent pets - or at least don't bother humans, while other's attack and kill?
Is is genetics? Are some dogs born bad and some good?
Or is it early imprinting? The influence people and/or other dogs have during the first few weeks of a pup's life.
Is there a canine equivalent to a human psychopath - and, on that note, are human psychopath' born or made?

I have met many strays and ferals - some in loose packs, some solitary. In Spain, in Greece and in Canada. My experiences were always good ones. The dogs were approachable, soliciting, at worst keeping their distance, but never attacking.
I have met a rescue pup, born to a feral mom, that relentlessly and seriously attacked other dogs at a very young age (after weaning), while all other litter mates were normal, middle of the road pups.
I have first hand knowledge of a pup born spitting, 'mean' almost the moment she popped out of her mother's womb. Born to a very knowledgeable and conscientious breeder and of a breed described by one dog book as the least likely to bite.

So what is it? Nature or nurture? Probably both. Which brings up another question? Is it okay to euthanize a pup we suspect is born bad, even if he/she is very young, and without having tried rehab?