Even though bats and birds didn't evolve from a common ancestor, they both have wings. This phenomenon, called convergent evolution, sees species in similar ecological niches evolving similar adaptations—not because they’re closely related, but because they’re faced with the same evolutionary problems.

Giant pandas and red pandas are a great example of this. They diverged around 43 million years ago, with giant pandas in the family Ursidae along with other bears, and red pandas as the lonely living representatives of the family Ailuridae, more closely related to ferrets (take a look at giant pandas and red pandas on this zoomable tree of life). But both kinds of panda are unique among the carnivores in that they're exclusively herbivores.

That lifestyle choice has apparently left similar marks on their genomes, as a team of researchers found when they sequenced the red panda genome.

Both giant and red pandas have adapted to an extremely specialized bamboo diet, which means important adaptations to their digestive systems. Bamboo is a tough, fibrous food that is difficult to digest. Pandas, with their digestive systems inherited from carnivores, have had to undergo some major changes to absorb the scant nutrition available in their chosen food. Pandas also share a weird and fascinating adaptation to their paws: they both have a “pseudothumb,” with a bone that protrudes near the paw and makes it easier to hold onto a stick of bamboo.

The researchers were interested in whether they could find similarities in the two genomes that could shed light on how these similarities evolved. To do this, they sequenced the red panda genome, which is starting to sound easy these days but is still a labor-intensive task. Because sequencing methods have continued to improve, they also did a bit of cleaning up of the already-sequenced panda genome, to make sure that both were of comparable quality.

Then, they compared the two genomes with the published genomes from six other species: the polar bear, ferret, dog, tiger, human, and mouse. This allowed them to look for unexpected similarities in the panda genomes that might be suggestive of convergent evolution. They identified 70 genes that seemed to be likely culprits.

Drilling into the specifics of these 70 genes turned up some interesting results. For instance, two of the genes, called DYNC2H1 and PCNT, are known to be involved in limb development. When something goes wrong with them in mice or humans, the result is abnormal skeletal growth. It seems likely, the authors write, that these genes “contribute to pseudothumb development in both pandas.”

Various other genes on the list are likely to help the pandas' digestion. Some of the genes are known to be involved in protein digestion, while others help with the uptake of vitamins A and B12, which are in low supply in bamboo. And in both species, the umami taste receptor gene TAS1R1 has been “pseudogenized”—it can no longer produce a functional protein. “Umami is a critical taste sense for meat-eating animals,” the authors write, and the loss of function “may be an evolutionary response to the dietary shift from carnivory and omnivory to herbivory.”

It’s pretty easy to see convergent evolution at the level of observable characteristics. We’ve known for ages that bats and dolphins both use echolocation, and we’ve been able to observe how different species hit on the same evolutionary solutions to things like particular diets or threats. But although it’s a widely observed phenomenon, it’s still something we’re only just starting to see at the level of the genome.

This is a fascinating glimpse under the hood of convergent evolution, but there’s still a lot more research to be done to confirm that the changes in these genes actually impact the pandas' ability to function as a vegetarian.

PNAS, 2016. DOI: 10.1073/pnas.1613870114 (About DOIs).