None of this could have happened if we hadn't split humans into body and spirit and claimed that bodies were completely irrelevant and spirit was all that mattered. This is NOT Christianity, it's the heresy of dualism. But Western civilization is immersed in it without even being fully aware of this.
This is how people can base their lives and families on the idea that nurture is what truly matters, and nature only provides the lowly base materials we'll get to form in our own image. That love is all you need. That family is defined solely on the basis of feelings, intentions, conditioning. That where our bodies came from has nothing to do with ourselves and who we are and how we feel and think and act.
Those who were raised by their biological parents can do this more easily - they can draw the nature/nurture, body/spirit, DNA/upbringing line wherever they please and claim "I didn't INHERIT my temperament from my mother, I'm like that because she raised me." They have the privilege of wholeness and integrity that they can then divide at will, drawing that imaginary line where they need or wish it to be.
Those not raised in their biological families know different. But they lack even the proper terms to express a desire for wholeness in a culture steeped in dualism.
Here's a great post on dualism in adoption by a Catholic priest who's an adoptee.