Squid Reveals Evolutionary Purpose of Pain: Keeping Us Alive After Injury

It turns out that squid may be able to tell us a little bit more about pain and why we experienced heightened sensitivity after an accident or injury. Scientists have found that squid that experience pain are far more likely to live to see another day.

"Many pain researchers and clinicians consider long-lasting sensitization and associated pain to be maladaptive, rarely considering whether it might be evolutionarily adaptive," said Edgar Walters, one of the researchers, in a news release. "Intense pain is certainly maladaptive in many human contexts when modern medical care is available. However, this study provides the first direct evidence for the plausible evolutionary hypothesis that sensitization mechanisms-which in some animals are known to promote pain-have been shaped by strong evolutionary selection pressures, including pressures from predators."

The researchers took a closer look at how squid reacts to pain in order to get a better sense of how evolution may have played a role in pain adoption. They watched squid and black sea bass swimming freely in laboratory tanks. When a squid was injured, it was often pursued by the bass-and the squid, in turn, acted more defensively.

What was interesting was the survival value of heightened vigilance to the injured squid. In fact, the scientists found that squid treated briefly with anesthetic actually failed to respond with enhanced defensive behaviors that would otherwise help keep them alive.

"If we can understand more about what the natural, 'intended' purpose of nociceptive sensitization is, we might be in a better position to find new ways to treat its pathological expression in humans," said Robyn Crook, one of the researchers, in a news release.

The findings reveal a little bit more about how pain evolved in species. More specifically, it reveals how pain can perform the critical function of keeping us alive when injured.

The findings are published in the journal Current Biology.