If a mother is out shopping and hears a young child crying out “Mommy!” she will turn around. This will happen almost every single time, even if she knows her children are at home or off at college. This ability to recognize and respond to the distress call of someone else’s offspring isn’t just limited to humans. After noticing that most mammalian babies sound fairly similar when crying, Susan Lingle of the University of Winnipeg performed a study and found that wild deer in Canada will respond to the cries of several mammalian species. The results were published in The American Naturalist.
While dogs have been known to respond to a crying human baby, it hasn’t been clear if this is because of a commonality between mammalian infant cries or merely because of familiarity due to thousands of years of domestication. To remove any chance of familiarity affecting the study, Lingle and Tobias Riede of Midwestern University obtained recorded distress cries of infant mammals that had been separated by tens of millions of years of evolutionary history. The recordings were played to wild deer through speakers and included the infant cries of seals, marmots, cats, bats, and humans.
When the cries were within a range that female deer are used to hearing from their offspring, they were quick to try to locate the infant from the recording, regardless of species. If the call was outside the desired frequency range, the cry would get the doe’s attention, but she would not move toward the sound. If the researchers adjusted the frequency to fall within range and did not manipulate the recording in any other way, the deer would quickly respond and try to find the baby.
The researchers also played sounds from adult deer and local predators including coyotes, which did not provoke a response. Additionally, the deer did not respond to distress calls from songbirds or to calls that were within the desired pitch range but not structured the same as natural infant mammal cries.
Though there are differences in pitch and duration between species, there are also features that have been evolutionarily conserved. It is likely that early in mammalian history, mothers needed to protect their babies and protect them quickly. A tone that would have caused the quickest response would have been highly selected for, and would have become highly conserved throughout history. The researchers suggest that this is an example of cross-species sensitivity that isn’t bound by human empathy or familiarity. This could mean that there are other areas of behavior and emotion that are able to transcend between species as well.
[Hat tip: New Scientist]