When you sit down for Thanksgiving dinner this week, you’ll use all five of your taste receptors—sweet, bitter, sour, salty, and umami, also known as savory— to enjoy every morsel of the annual feast. Without these important sensory receptors, you wouldn’t be able to detect the bitter beans in a green bean casserole; the tangy fruit in cranberry sauce; the sweet filling in pumpkin pie; the saltiness of melting butter on a sweet potato; or the savory meat of the Thanksgiving turkey.
But some animals, including penguins, possess far fewer taste receptors—a difference researchers think may be due to the Antarctic environment where these birds evolved.
How Taste Works
Our taste receptor cells are located on our tongues and soft palate, inside thousands of papillae called taste buds. The primary purpose of these cells is to help us find nutritious fare or to act as the body’s first line of defense against foods we shouldn’t eat. Sour and bitter act as warning systems for foods that have spoiled or may be poisonous, while sweet and savory receptors help to identify sugars and proteins essential to our diets.
Salty and Sour
Penguins, however, seem to have lost three of the five receptors. In a 2015 study led by then-University of Michigan professor Jianzhi Zhang and published in the journal Current Biology, scientists examined the genomic sequences of 16 species of birds, including Pygoscelis adeliae (Adelie Ppenguin), Aptenodytes forsteri (Eemperor Ppenguin), and Egretta garzetta (Little Egret). The team concluded that while all of the birds analyzed lacked the sweet receptor, penguin species also lacked bitter and umami—leaving them with the ability to taste only sour and salty.
Researchers think that drastic cooling in Antarctica millions of years ago may have affected the taste receptors of the penguins’ common ancestor. One potential reason: a protein that’s responsible for sending sweet, umami, and bitter taste signals to vertebrate nervous systems doesn’t work well at lower temperatures.
Penguin Tastes
Before the genetic study was carried out in 2015, researchers had seen anatomical evidence that penguins weren’t exactly supertasters. While human tongues have four distinct types of papillae located in our taste buds, a 1998 study from scientists at the Nippon Dental University in Niigata, Japan, found that penguins only have one.
“Their behavior of swallowing food whole, and their tongue structure and function, suggest that penguins need no taste perception, although it is unclear whether these traits are a cause or a consequence of their major taste loss,” explained Zhang.