Scientists Study Why Human Women 'Nest'

A few days before my younger son was born I found myself, immensely pregnant, sitting on the family room floor and sorting my older son’s stuffed toys by size and color. Then I moved on to the drawer full of onesies and stacked them by size and color too. It felt urgent and important that this be done before the baby arrived. It also made absolutely no sense, which I knew even as I continued to do it.

I understood that I was “nesting” -- the pregnancy books told me so. It was one more reminder that we are all, at our core, just mammals, ruled by hormones and electrolytes as much as personality and free will.

A study of nesting in this month’s issue of the journal Evolution and Human Behavior attempts to apply a scientific lens to what every woman who has ever been pregnant already knows -- that we can’t help ourselves. Using both an online survey and a longitudinal tracking study comparing women who were pregnant with those who weren’t, researchers at McMaster University in Hamilton, Canada found: that nesting peaks in the third trimester; that the behaviors involved are more often ones of organizing and sorting rather than cleaning and disinfecting; and that it includes the sorting of people as well as things, as seen in a tendency to retreat to the comfort of home and the company of familiar people.

And WHY do we do all this? Because that’s what our ancestors did, the authors theorize. Back when there were caves to be readied with soft moss and animal skins, back when wild predators could outrun a very pregnant woman should she stray too far from home, this was nature’s way of telling us it was time to ready the roost and circle the support.

Of course, the particulars have changed, and now we have so many more ways to nest than just cozying up the corner of a cave. As described in the study, women report some rather odd behaviors and birth nears -- things like dismantling the hardware on kitchen cabinets to disinfect the screws and knobs; cleaning the house top to bottom with a toothbrush; throwing out all the “old” bed and bath linens because only fresh, new ones will do.

Once the baby arrives, these urges seem to stop, either because the triggering hormones recede or the post-partum mother is just too busy and tired to clean anything with a toothbrush, often including her own teeth.

What is the craziest thing you did while nesting?

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