Why must anything murder to stay alive?

[daveb]

4 hours ago, Sherlocks said:

Wouldn't this fall back to the old rabbit vs wolf concept, though? If there are a lot of rabbits the population of wolves will go up but if they start eating too many rabbits the wolf population would drop. In fact, this concept has happened with species in today society. Either they don't have enough ecosystem and populations drop, or they run out of things too eat and populations drop. 

Not sure what you're getting at with this? What you're saying is basically one of the main reasons why some creatures need to kill other creatures, so you're answering your own question in your OP. Yep, if you have organisms that reproduce death has to happen to keep populations from increasing ad nauseum until they overload their ecosystem, which then leads to massive depopulation as many of the organisms die from lack of food.