This is a question that just occurred to me. What makes one species of animal die "harder" than another that is similar in biological function? For example, let's think about Whitetails and Dall Sheep. They are similar size, and similar construction (relatively speaking) but there is a big difference in the will to live, at least in my experience. The same could be said about Moose and Elk. Although I have never hunted Elk, the opinion is that they are much tougher to kill than your average moose.
My question is why? Is it purely more instinct to survive? More sprit engrained in that particular species? If so how did that happen? What drives it?
I thought this may make for an interesting discussion.