Buddhism affirms the unity of all living beings, all equally posses the Buddha-nature, and all have the potential to become Buddhas, that is, to become fully and perfectly enlightened. Among the sentient, there are no second-class citizens. According to Buddhist teaching, human beings do not have a privileged, special place above and beyond that of the rest of life. The world is not a creation specifically for the benefit and pleasure of human beings.
Furthermore, in some circumstances according with their karma, humans can be reborn as humans and animals can be reborn as humans. In Buddhism the most fundamental guideline for conduct is ahimsa-the prohibition against the bringing of harm and/or death to any living being. Why should one refrain from killing? It is because all beings have lives; they love their lives and do not wish to die. Even one of the smallest creatures, the mosquito, when it approaches to bite you, will fly away if you make the slightest motion. Why does it fly away? Because it fears death. It figures that if it drinks your blood, you will take its life. . . . We should nurture compassionate thought. Since we wish to live, we should not kill any other living being.
The karma of killing is understood as the root of all suffering and the fundamental cause of sickness and war, and the forces of killing are explicitly identified with the demonic. The highest and most universal ideal of Buddhism is to work unceasingly for permanent end to the suffering of all living beings, not just humans.