Pandas are famously peaceful creatures, content to sit around quietly eating bamboo. But millions of years ago, they were as fierce and carnivorous as the rest of their bear relatives. It's all a question of changing environments and shifting genes.
Genetic research into pandas by Jianzhi Zhang at the University of Michigan found that pandas now carry an inactive version of the Tas1r1 gene. This gene controls the ability to taste umami flavors, which includes all meaty and savory flavors. Without it, pandas can't really taste meat, and so they probably wouldn't want to eat meat even if it was available in large quantities.
But how did the pandas lose the gene in the first place? Well, we know that the gene has been inactive for 4.2 million years, and that the fossil record shows us that pandas switched from meat to bamboo anywhere from 7 to 2 million years ago. Previous research has suggested environmental changes killed off most of the panda prey, leaving them no choice but to turn vegetarian in order to survive.
So, after the prey died out and pandas started eating bamboo exclusively, the Tas1r1 gene became pretty much pointless, and it eventually stopped working. That's a neat theory, but it only works if pandas made the switch between 7 and 4.2 million years ago - the fossil record leaves the possibility open that it happened after the gene switched off. That's a much harder story to explain, but it's not necessarily impossible.
[via New Scientist]