My dad asked me the other day why the baby puts everything in her mouth, and I told him my theory:  she's developing her immune system by exposing herself to all the germs in her environment.  Much of our immune system is acquired after birth as we build antibodies to the microbes we come in contact with.  While she's processing all these new microbes, my breastmilk helps her not to get horribly ill by passing antibodies to her before her body has made its own.  I think it's brilliant, then, that she is somehow compelled to put her hands in my mouth as well.  She's exposing both of us, so that if she's gotten into anything truly nasty, she can get her main protection from me.  I don't know necesarily that all the hands-in-my-mouth thing is truly an evolutionary adaptation as I'm postulating here, but it makes so much sense.  Working within the midwifery model has given me a certain faith in the workings of our bodies -- midwifery is all about trusting the body to birth if left to its own devices.  Looking at our other adaptations, especially as relates to infancy and breastfeeding, I am more inclined to trust that our bodies have wisdom in these areas as well.