New dads that co-sleep with their children may experience a drop in their testosterone, says results from a recent study in the Philippines.

The findings are in a scientific journal called PLoS ONE, (which is ranked as the least sexy science journal) and come to us from Lee T. Gettler and company. Remember that name.

Gettler took a cast of 362 Filipino dads and choreographed a prison dance party took testosterone samples in 2005 and 2009. Researchers analyzed whether the Filipino dudes coslept with their kids, slept in the same room, or slept in different rooms than their kids.

Here’s what Gettler and company found:

Compared to fathers who slept solitarily, same surface cosleeping fathers had significantly lower evening (PM) T and also showed a greater diurnal decline in T from waking to evening (both p<0.05). Among men who were not fathers at baseline (2005), fathers who were cosleepers at follow-up (2009) experienced a significantly greater longitudinal decline in PM T over the 4.5-year study period (p<0.01) compared to solitary sleeping fathers. Among these same men, baseline T did not predict fathers’ sleeping arrangements at follow-up (p>0.2).

Or, in layman’s terms: lower testosterone for co-sleepers. And what was surprising was that there was no predictor for a father to be a co-sleeper based on initial testosterone levels (ruling out that men with lower testosterone would be more likely to co-sleep).

The findings suggest that fathers that co-sleep are biologically rewiring themselves for caretaking. Scientific American notes that “high levels of the hormone are linked with aggression, risk-taking, and less sympathy for an infant’s cries,” so it’s possible that as the body is telling us an incredible story about biological roles and how we adapt to those roles when they aren’t what the body expects.

Get this: last September, we told you that new dads experience a drop in testosterone, regardless of sleeping pattern. That study was also a study helmed by Lee Gettler, using testosterone samples from the Philippines. Coincidence? I think not.