I always thought of family as a bunch of people that you're born related to. Over the course of my 40-ish years I now know that there are people that are loved as much as family that don't necessarily share any genetic link. I have 3 daughters that share my husbands genes and that I didn't give birth to but that I love with all my heart. I have step-parents that own pieces of my heart. I'm not sure where the term "step" parents or "step" sibling came from. There really is no "step" involved in the love that we share. I have friends who were there when I needed them most and they are as important as my family.
On the flip side, I have family that I know very little about. In a sad twist, divorce causes distance between people. Children are left with emptiness on entire sides of their family tree. Regretfully, I caused this very thing to happen to my own children. They have relatives that they may never know and for that I wish I could turn back the clock and keep those distances from happening. I resemble my dads family and have relatives that share my bone structures and eye color but who I don't know very well. Still, the genes that we share make it easy to love them as if we were never separated. My boys have cousins and aunts and uncles that I wish they knew but hindsight is 20/20 and they will need to decide if they want any of these relationships to bloom.
In these days of social media maybe fewer of these situations will occur. Maybe distances won't matter and relationships will naturally occur. I'm not sure that it's true that chance makes us family but choice makes us friends. I think there is a little chance and choice in all relationships.