Your children are not your children.
They are the sons and daughters
of life's longing for itself
— Kahlil Gibran
The New York Times article on the new study about reduced testosterone in fathers starts off with a bang of inaccuracy: "Testosterone, that most male of hormones, takes a dive after a man becomes a parent."
This isn't what the study showed. In fact, as far as I can tell, there was no control group of men who spent time with children they hadn't sired, which would be the control group necessary to demonstrate that becoming a parent was the experience that triggered the reduction in T. The following sentence furthers the untested assumption that this effect is about being a biological father: "The more he gets involved in caring for his children — changing diapers, jiggling the boy or girl on his knee, reading 'Goodnight Moon' for the umpteenth time — the lower his testosterone drops."
If, in fact, the study showed that this effect only applies to a man caring for his children, then it may be warranted to describe this as a study about "the biology of fatherhood." Only near the end of the article, is primatologist Sarah Hrdy (author of "Mothers and Others") quoted asking the crucial question: Would similar results occur “if you have an uncle or brother or stepfather living in the household and they care for the baby?”