... capacity is of two kinds:

... capacity is of two kinds: natural capacity and acquired capacity. The first, which is the creation of God, is purely good--in the creation of God there is no evil; but the acquired capacity has become the cause of the appearance of evil. For example, God has created all men in such a manner and has given them such a constitution and such capacities that they are benefited by sugar and honey and harmed and destroyed by poison. This nature and constitution is innate, and God has given it equally to all mankind. But man begins little by little to accustom himself to poison by taking a small quantity each day, and gradually increasing it, until he reaches such a point that he cannot live without a gram of opium every day. The natural capacities are thus completely perverted. Observe how much the natural capacity and constitution can be changed, until by different habits and training they become entirely perverted. One does not criticize vicious people because of their innate capacities and nature, but rather for their acquired capacities and nature. 

 Bahá’í World Faith—Selected Writings of‘Abdu’l-Bahá