To live means to be part of a timeline that we share with other living creatures. The core purpose of every living creature is to insure its continued survival on this timeline. Some living creatures, like humans, have developed an awareness to its surrounding which gave them the ability to set different, but not so different (as the root of every goal is survival), goals for itself.
Some humans are selfish, or does things to insure their own survival, and some are selfless, or who do things to insure the survival of others including or excluding themselves. Both of these groups want to survive but one could say that selflessness is better because it benefits a group rather than an individual.
To me, it make sense to have a group of living creatures, like Foxes, fight off another group, like rabbits, for survival but where it doesn't make sense is when you have individuals of a same specie fighting each other for supremacy/survival.
Primates, for example, have groups that will fight off primates, from another group, that entered their property. Because these two groups can't cohabit they're effectively limiting the specie's potential to grow. One would think that a group could become so big that it could conquer every other group, and then grow exponentially, but what tends to happen, with the case of primates at least, is that big groups separates to form smaller groups and the cycle repeats itself.
I've purposely chosen primates in the example above because humans have commons ancestors with them and we can certainly see similarities in regards to behaviors. The societies that we've created for ourselves might be a bit bigger and more complex but the idea behind those societies remains the same - we form these groups in order to survive and we will fight off invaders just the same as our primate ancestors did.
At a much smaller scale, the workplace has people fighting each other to rise up that corporate ladder which, to me at least, is the same as having 2 primates fighting each other for group dominance. The type of society we've built is definitely a progression of the primate's territorial mindset.
Our society, unlike Primates' societies, has evolved to the point where we've included such things as personal freedom and equal rights. It's now possible, for example, to have women occupy roles that used to be reserved for men something not accepted in primate societies. Progress is slow but these are indicators that we're moving away, at least in some areas, from our primitive instincts in favor of a, perhaps, more logical approach to the way of living our lives.