Lab mice are afraid of men, according to a new study. But not women.
And while that might just sound like a custom-built lead-in to a 1970s comedy routine, it's actually a pretty serious problem for science.
Because it might mean that an implicit bias has been built into thousands of experiments over the decades, and no one had a clue.
Jeffrey Mogil, a researcher at McGill University, said in his study that mice experienced more stress when exposed to the smell of men than women. They tested this using the 'mouse grimace scale', which uses pain as an inverse indicator for stress, since stress tends to numb pain.
The study also showed that rodents exposed to men had higher levels of the stress hormone corticosterone, and a higher body temperature, compared to exposure to women. And the effect was also present when exposed to the smell of male dogs, cats and guinea pigs, not just women.
The results (full study here) indicate that rodents react instinctively to the presence of males in order to defend their territory, rather than out of fear of being eaten.
"It’s a primordial response. If you smell a solitary male nearby, chances are he’s hunting or defending his territory," Mogil told Science Magazine.
"It’s really astounding that such a robust effect could have been missed for so many years."
The problem is that many other experiments on lab mice also test stress levels, but until now there has been no reason to control for the gender of the experimenter - or even to report it in the studies.
It doesn't mean that all the studies undertaken involving lab mice are wrong - but it does mean that there is another reason to doubt them, or to look again at unusual results that have gone unexplained - especially since tests on mice remain so crucial for the development of vital medical drugs.
"It’s a confounding factor, but not a fatal one," said Mogil. "I joke that the solution is to fire all the male researchers,” Mogil says. “But at the very least, this is something teams should be noting in the methods sections of their papers. We can change the bath water without throwing out the baby."Suggest a correction