A number of deep-dwelling sharks have special light-emitting organs on their undersides that allow them to glow.
A study of pygmy sharks now suggests the ability to control the trick evolved from a shallow water ancestor.
Dr Julien Claes from the Catholic University of Louvain in Belgium led the research.
He said: “bioluminescence remains one of the most mysterious areas of shark biology.”
The findings are published in the Journal of Experimental Biology.
According to Dr Claes more than 10% of currently described shark species are luminous.