Blinking helped our ancestors evolve from water to land, finds study

Examining the blinking behavior of the fish

This study shows how these amphibious fish evolved blinking behavior, which could help explain how this trait appeared in our ancestors.

Blinking, it turns out, was one of the characteristics that allowed the transition to life on land in a group of animals called tetrapods, which includes mammals, birds, reptiles, and amphibians. This evolution occurred approximately 375 million years ago, as per the study.

“Studying how this behavior first evolved has been challenging because the anatomical changes that allow blinking are mostly in soft tissues, which don’t preserve well in the fossil record. The mudskipper, which evolved its blinking behavior independently, gives us the opportunity to test how and why blinking might have evolved in a living fish that regularly leaves the water to spend time on land,” said Stewart. 

The researchers used high-speed video to monitor this trait in the fish closely. They then compared its anatomy to another water-bound fish that doesn't blink. This helped to reveal the anatomy of the mudskipper's eyes, which allowed the fish to blink. The eyes of the creatures usually protrude from their heads, as seen in frogs. When the fish needs to blink, they move their eyes down into sockets protected by a stretchy membrane called a "dermal cup."  

“Blinking in mudskippers appears to have evolved through a rearrangement of existing muscles that changed their line of action and also by the evolution of a novel tissue, the dermal cup. This is a very interesting result because it shows that a very rudimentary, or basic, system can be used to conduct a complex behavior. You don’t need to evolve a lot of new stuff to evolve this new behavior — mudskippers just started using what they already had in a different way,” explained Aiello.

The team also noticed that mudskipper and human blinks are nearly identical in length. Furthermore, the reasons why mudskippers blink on land are similar to the roles blinking plays in our lives. Even though mudskippers do not have tear glands or ducts, they still blinked frequently when exposed to dry eyes. The fish created a tear film by combining mucus from their skin and water from their surroundings.

The results have been reported in the journal Proceedings of the National Academy of Sciences.