I've never felt this urge, not even remotely. I wish this study had more info, percentages, male vs female, age, parent or not, etc. Curious.
For their experiment, the researchers presented two groups of 15 women with the odours of others' newborns while the women were subjected to brain imaging tests. The first group was composed of women who had given birth 3-6 weeks prior to the experiment, and the other group consisted of women who had never given birth. All the women were non-smokers. The odours of the newborns were collected from their pyjamas two days after birth.
It is also not known whether this reaction is specific to mothers, since men were not part of the experiment. “What we know now and what is new is that there is a neural response linked to the status of biological mother," he says.
Looks like a very small sample size, but still interesting. Though I'm wondering more whether that cake has doll parts attached to it or carefully sculpted icing or something.