Animals kill their own kinds only for two reasons:
1. To eat to survive
2. To ensure their genes are passed on to their offsprings eg. A male lion kills other male lions cubs (looks cruel but necessary) to ensure the lioness comes in heat and thus it can mate and have its own cubs. A male lion usually have only 2-3 years to control the pride before it is chased away by the younger and stronger male lions.
In contrast, humans kill other humans for much lesser reasons such as:
1. Unpaid debts
5. Skin colour
6. Materials such as money, car, etc
7. Crying babies
9. Car overtaking
10. Women, Men
12. Power, etc etc
13. Parliamentary seat
Just ponder about this. We are blessed with sophisticated brain, but why all the killings?