The whole purpose of this assignment is not simply to answer the question.
It is to make you think about how it has affected the human race in a positive way.
Dig deep and look for the positive things in your life. Volunteer a few hours a week at a pet shelter, homeless shelter, library, etc. You won't believe how much your attitude towards life will change for the better.
You matter just because you exist.
You also matter because you have something to offer others.
Embrace and believe it.
That will help.