Japanese researchers say they have discovered that some species of sharks and rays have bitter taste receptors similar to those of human beings.
They say the bitter taste receptors may date back to 450 million years ago when primitive fish species, which are believed to be the ancestors of humans, evolved into rays and sharks.
A team from Meiji University and a research institute that studied the evolutionary origins of bitter taste receptors, recently published their findings in Current Biology.
They claim to have discovered in red stingrays and bamboo sharks the TAS2R genes also found in humans. They say these genes are expressed in oral sensory organs called taste buds.
They say that some species of primitive fish, which are the ancestors of humans, evolved into stingrays and sharks some 450 million years ago, and it is likely that bitter taste receptors already existed then.
The researchers speculate that the primitive fish species acquired jaws, and the ability to eat a variety of foods, and that bitter taste receptors developed to prevent them from mistakenly eating something toxic.
Itoigawa Akihiro, a researcher at Meiji University, says it is interesting that humans today can enjoy the bitter taste of things such as beer and coffee with receptors that were acquired 450 million years ago.