Evolution may explain why whales can’t taste

The sense of taste is largely dependent upon groups of cells on the tongue called taste buds. In mammals, each taste bud cell confers one of five particular tastes: sweet, umami/savory, bitter, sour or salty. Since our tongues are one of the first parts of our bodies to interact with the food we eat, being able to convey information about the nutritional content of your snacks can be crucial for your survival.

Taste bud
Taste bud

Sweet is associated with, you guessed it, sugars: foods high in calories and therefore precious to consume. As such, your body tells you “eat more, eat more!” since it doesn’t know the next time you’re going to come across a candy bar. On the other side of the spectrum, bitter is often associated with toxic compounds, such as those in plants used to defend against herbivores, so for many animals it triggers an aversive response.

So how do these taste cells confer different tastes? Each cell expresses a different set of proteins that binds the molecules we associated with taste. So, for example, your sweet proteins bind things like glucose and sucrose, as well as artificial sweeteners, whereas there are bitter proteins that bind things like strychnine.

Screen-Shot-2013-09-14-at-2.52.32-PM
Mammalian taste receptor proteins and molecules that activate them.

But while humans and many other mammals chew their food, in the process getting a good taste of what they’re eating, some animals, like whales, pretty much just swallow their food whole. In fact, whales do not appear to have any taste buds at all, consistent with their grab-and-gulp method of eating.

Yet DNA and fossil evidence suggests that whales descended from terrestrial hoofed mammals that were largely plant eaters, and as such would have chewed their food and would have had a lot of use for taste buds. Is there any evidence to support this?

Indeed, when researchers looked for the genes encoding taste receptor proteins in whales, they discovered that the genomes of whales have remnants genes involved in sweet, umami, bitter and sour taste [1]. What’s more is that several of the genes have identical inactivating mutations shared by multiple whale species, suggesting that the genes were knocked out in a common ancestor.

PKD2L1 pseudogenes in whales.
PKD2L1 pseudogenes in whales, encodes a protein involved in sour taste. Inactivating mutations highlighted by boxes.

This suggests that while Shamu here wouldn’t particularly enjoy an ice cream cone, his land-dwelling ancestors just might have.

Orca tongue

Questions for Creationists

Why would the Creator design whales with taste genes that are nonfunctional, especially when whales don’t have taste buds? Why did It create multiple whale species that share identical inactivating mutations? Is it just a coincidence that DNA and fossil evidence suggests that whales descended from plant eaters that walked on land, and plant eaters have all of these taste genes intact?

References

1. Feng, P., Zheng, J., Rossiter, S. J., Wang, D., & Zhao, H. (2014). Massive losses of taste receptor genes in toothed and baleen whales. Genome biology and evolution6(6), 1254-1265.

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