Last year, Israeli neuroscientists Shani Gelstein and Noam Sobel published a study about mind-control properties in human tears. The gist of the research, which enjoyed much media attention, is that women’s tears contain a chemical signal that reduces sexual desire in men. Gelstein and Sobel collected teardrops from the cheeks of women who were watching sad films and and then wiped those excretions on the upper lips of male volunteers. Compared to men who whiffed a salt solution control, the tear-sniffers not only had a reduced sex drive but also lower testosterone levels and reduced brain activity.
The explanation: Chemicals in tears may reduce male aggression and make them more sympathetic.
How does this work? One theory is that one or more of the hundreds of chemicals in tears has “mind-control” properties, triggering specific predictable behaviors in others. (Here and here I write about how this happens in sweat, too.) One candidate is prolactin, a hormone associated with bonding. Prolactin may affect the sniffer’s hypothalamus, the part of the brain that produces hormones which in turn affect behavior.
Are there also chemicals in babies' tears that manipulate caregivers?
Baby tears have not been the subject of a study yet (hopefully soon). But it’s not a far cry from certain that if there are chemicals in the tears of women that affect men, there are also chemical triggers in the tears of babies that affect their caregivers -- or anyone else that comes into contact with them. These tears may trigger care-giving instincts and reduce aggression toward the screaming infant.
I wonder: Infant abuse is relatively uncommon given how irritating a screaming baby can be. Are the people guilty of this crime more likely to be amnosiacs (loss of smell-sense) or have another form of brain damage that would prevent them from inhaling aggression-reducing signals in the baby’s tears?
Another theory: Kids cry all the time, and sometimes it’s hard to tell when they really need attention. Might chemicals in emotional tears direct parents to respond appropriately when there is a real need for attention? Assume that these chemical signals are only in emotional tears–not crocodile tears or sleepy-time tears. Do they help us intuitively know when it's better to step in and soothe --or just lay back and ride the tide?
*If you like this blog, click here for previous posts. If you wish, check out my new book, Do Chocolate Lovers Have Sweeter Babies?: The Surprising Science of Pregnancy.