Men may not go on a hormonal rollercoaster with their pregnant partners, but once the baby shows up, their bodies biologically transition into "daddy mode," suggests a new study finding that levels of testosterone, the "macho" sex hormone, drop in new fathers. "Men are, to a certain degree, hardwired to take care of their kids," study researcher Lee Gettler, of Northwestern University in Chicago, Illinois, told LiveScience. "This is important because traditional models of human evolution have portrayed women as the gatherers that take care of the kids and stay behind."
The hormone drop makes sense, the researchers say, since high testosterone tends to boost behaviors linked to competing for a mate, risky activities that may conflict with the responsibilities of fatherhood.