OK, but what about old dad? He's also been yakking away during the pregnancy. Can a fetus recognize his voice as well?
Maybe, but that's not known yet. That's the next phase of the research, Kisilevsky says. Of course, dad isn't around the fetus as much as mom, and whether the baby recognizes pop may depend on how much the kid has heard him talking.
There may be a threshold at which the fetus learns to recognize dad, thus sending the heartbeat up, but that isn't known yet.
Incidentally, we begin losing some of our innate ability as soon as we are born.
According to Kisilevsky, other research shows that a newborn infant can discriminate different sounds in virtually all languages.
"Over the course of the first year you lose discrimination ability and you then become only able to discriminate the sounds in your language," she says. "It seems that infants really are set up to learn language, and it doesn't really matter which language it is."
But as we learn one language, it gets much more difficult to understand the sounds of other languages, as any adult who has struggled to learn a foreign language knows all too well.
Maybe it just shows that those tiny humans, so frail and vulnerable, are also banging at the starting gate, well equipped for at least part of the task ahead.
Lee Dye’s column appears weekly on ABCNEWS.com. A former science writer for the Los Angeles Times, he now lives in Juneau, Alaska.