Unlovable Sea Lampreys Might Share Our Fight-or-Flight Instinct

If you vacationed on the Great Lakes in the summer after the COVID-19 pandemic hit, you may have had the misfortune of spotting a sea lamprey wriggling through the shallows. The population of this parasitic eel-like fish—an invasive species that can be easily recognized by its unsettling, suction cup-like, tooth-filled mouth—skyrocketed during lockdown.

“We’re very happy that they’re not cute like bunnies,” Greg McClinchey, a policy director for the Great Lakes Fishery Commission, told the Wall Street Journal at the time, “because it would be much harder to convince people that we need to [get rid] of them. They are unquestionably the stuff of nightmares.”

And yet, the bloodsucking fish may resemble humans more than we’d like to think.

From Larvae to Lamprey

Sea lampreys, which start their lives as filter-feeding larvae and can reach up to 20 inches in adulthood, owe their unusual appearance to their relatively distant position on the evolutionary tree. The species emerged more than 350 million years ago in the Late Devonian period, although some studies suggest they are even older: their jawless mouths are a relic from a time before fish—and, by extension, we—gained the ability to bite and chew.

Because a lamprey’s physiology changes drastically over the course of its life, the species has proven difficult to study. Despite these challenges, a team of scientists from the California Institute of Technology has managed to get an unprecedentedly clear look at the animal’s nervous system. The result of their research, published in the journal Nature in April 2024, sheds light on the lamprey’s evolutionary relationship to other, less creepy vertebrates, like bunnies.

In short, the scientists discovered that lampreys have stem cells that appear to form the basis of a rudimentary sympathetic nervous system. It’s the same kind of nervous system that, in humans and many other species, produces a fight-or-flight response to threats, affecting the gut, pancreas, and heart to raise heart rate and blood pressure in stressful situations.

This makes lampreys some of the oldest known animals to have a sympathetic nervous system, forcing biologists to rethink when the basic survival mechanism it enables first evolved. But while the new study answers some questions, it raises many others, namely, whether the nervous system produces similar behaviors in lampreys as it does in other vertebrates.

At the same time, the scientists involved in the study feel confident that the stem cells found in this terrifying fish form the evolutionary basis for our own nervous system, making the bloodsuckers just a little less alien than they appear.

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