Many animals are omnivorous, having a variegated diet ranging from vegetation to fruit, meat to insects, and a host of other items. Consequently, being able to taste and distinguish these foods likely aids in acquiring items that satisfy particular dietary needs.
Having a specialized diet, on the other hand, eliminates the need to taste everything. For example, if an animal is adapted to exclusively eating plant material, it probably would not need to be able to taste meat. But what happens when an herbivorous animal descends from ancestors that ate meat? Can we find evidence that it used to be able to taste meat, but subsequently lost it?
The giant panda (Ailuropoda melanoleuca) is an animal that eats bamboo almost exclusively, but this contrasts with other bears, which are generally omnivorous. It also contrasts with the evolutionary family that bears belong to, known as the carnivorans. Carnivorans, which encompass dogs, cats, weasels, mongooses, hyenas, and others, appear to have adapted to eating meat some 60+ million years ago. Consequently, giant pandas are oddballs in this group.
So how did this shift in dietary preference affect the giant panda’s ability to taste certain kinds of food? Taste in mammals depends on the function of taste receptor proteins encoded by different genes. There is a gene for sweet, two for sour, one for salty, many for bitter and one for savory/umami, the flavor you associate with eating meats and cheeses.
Predictably, carnivorans typically have a umami taste receptor gene, but the giant panda’s copy has become a nonfunctional pseudogene [1,2]. This was discovered by Li et al. , who reasonably infer that this is due to the history of giant pandas specializing on eating bamboo. As giant pandas transitioned from eating meat to plants, they probably no longer needed to retain the ability to taste meat. Natural selection wouldn’t have weeded out any mutations that would lead the loss of function in the savory taste gene, and that would subsequently become the norm for giant pandas.
Questions for Creationists
It’s understandable why God might have created giant pandas without the ability to taste meat, but why would He create them with a nonfunctional version of the savory taste gene? Would it not have made more sense to create them without the gene altogether? Why do we see a pattern of taste receptor loss in both the giant panda and whales? Why did God create just one bear that specializes on eating plants?
2. Zhao, H., Yang, J. R., Xu, H., & Zhang, J. (2010). Pseudogenization of the umami taste receptor gene Tas1r1 in the giant panda coincided with its dietary switch to bamboo. Molecular biology and evolution, 27(12), 2669-2673.