Hey hey hey. Blood relationships are not entirely worthless. From a purely biological point of view a mother is compelled to be a good parent by the hormones and instincts generated by pregnancy. HOWEVER, while blood relationships do provide a basic foundation to family relationships, they are in the end ONLY A FOUNDATION, and it's entirely possible to be family with a different foundation.
Cause in the end, what is a family? It's the group that sticks around and cares for each other.