As Cavemen, we dads developed a strong protective instinct (Saber-toothed cats were a real problem), as well as a nurturing instinct. We were hands-on with our babies 24/7 in our little caves (talk about co-sleeping), except when out after an extra big mammoth because we had another mouth to feed. And when we got back, no doubt the little Neanderthal had learned to flash her blazing bright smile, which meant we put an even bigger mammoth on the list for our next grocery trip.

Recently two young surgeons asked me why they want to be home with their babies so much. Since my day job is working with trauma centers, I have met lots of hardworking surgeons over the years, and have never heard anything like this. I explained that they spent a lot more time with their baby than their fathers spent with them, and research indicates that the more time new fathers spend with their babies, the stronger the innate, chemically driven response to both protect and nurture kicks in. (They said that makes sense, and we agreed the more we dads develop our Caveman side, the better.)

To me, after 21 years of witnessing thousands of dads as rookies, veterans, and coaches, this is more compelling evidence that new fathers have reached a tipping point in which we have reversed the notion that caring for children is “women’s work,” and concluded that failing one’s child is no longer a socially acceptable option for a father. Another indicator is a poll commissioned by Match.com that found 24% of single men without children, compared to only 15% of single women, say they want kids. This was something that rarely crossed the minds of young men in my generation.

The main driver is also obvious and supported by new research: we love our babies, and the more time we spend with them, the more we love them. The Male Brain, by Louann Brizendine M.D., chronicles research that demonstrates that we dads are endowed by nature, in the form of subtle hormonal changes occurring in the months surrounding the arrival of our child, to both defend our families from threats, and cherish and care for our kids from birth. The key to the latter is to stay close to mom during pregnancy, and then get hands-on once our baby arrives, as this closeness and contact triggers our chemical reactions. Apparently, millenniums of evolution and socialization begin kicking in as we become fathers.

Seems the more we develop our Caveman side, the better.