What's this emphasis on biological? Are adoptive fathers sub-standard?
It's not a popular sentiment... But it was required as part of our certification in california. When separated from mom and dad, they call it the primal wound, but our society accepts separating children from one parent without any of the guilting they require adoptive parents to go through.
From a purely empirical standpoint, in aggregate, biological father's are the least likely to hurt or kill their children. Both adoptive father's and step father's are more likely to. Says nothing about individuals, but as a society it would behoove the powers that be to ensure most kids are raised by bio parents. And by far most states adopt this approach, even to the point of absurdity.