For men, crying is often considered unmasculine. However, when a male mouse sheds tears, it seems to be trying to assert its masculinity.
Japanese researchers have discovered that male mice release pheromones in the fluid that moistens their eyes.
“No one expected that sexual chemicals would exist in tears,” said Kazushige Touhara from the University of Tokyo in Chiba. Pheromones, chemical signals that convey messages ranging from fear to sexual desire, are typically found in high concentrations in human sweat and in the urine of mice.
It remains unclear whether mice cry for the same reasons as humans do. In this study, their tears were simply a result of a physiological response that keeps their eyes moist and comfortable.
Touhara noted that the pheromones in this secreted fluid might be recognized by females when they groom each other’s faces. These sexy cues could help females select potential mates.
In most vertebrate species, pheromones activate nerve cells in the vomeronasal organ located in the hard palate between the nose and mouth. Touhara’s team plans to investigate how different pheromone compounds affect that organ, which influences mating behavior. However, when they examined mouse urine for activating pheromones, they found nothing. After testing natural chemicals from other glands, they unexpectedly discovered the very same chemicals in mouse tears.
According to researchers, humans do not release pheromones in their tears. The pheromones found in mouse tears are produced by a gene that humans do not possess.
Nevertheless, he believes this work highlights the mystery of human tears: scientists still do not fully understand why we cry when in pain. “I think crying has more significance than we realize,” Touhara said.
M.T. (according to Nature)
