Nightmare fish may explain how our 'fight or flight' response evolved

These structures include both jaws and the sympathetic nervous system, which controls our involuntary fight-or-flight response that kicks on in dangerous or stressful situations.

But a new study, published Wednesday (April 17) in the journal Nature, reveals that lampreys have sympathetic nerve cells after all — suggesting that the vertebrate flight-or-flight response is more ancient than scientists expected.

"Studies like this help teach us how we were built over evolutionary time," Jeramiah Smith, a computational biologist at the University of Kentucky who was not involved in the research, told Live Science.

But when the researchers started dissecting lamprey larvae, they noticed the immature fish had structures that looked a lot like neurons running in a chain down the length of their bodies.

The discovery that these jawless fish have a fight-or-flight response places the evolutionary origin of this system about 50 million years earlier than scientists expected.

One is that the fish have a long developmental cycle; after a young lamprey hatches, it can spend years developing in a larval stage before maturing into an adult.