“In the material world the struggle for existence and survival of the fittest are laws because in the material world there is disparity between conditioned souls due to everyone's desire to lord it over the material resources. This very mentality of lording it over the material nature is the root cause of conditioned life. And to give facility to such imitation lords, the illusory energy of the Lord has created a disparity between conditioned living beings by creating the stronger and the weaker in every species of life.” (Shrila Prabhupada, Shrimad Bhagavatam, 1.15.25-26)