The evolution of sweetness is a fascinating example of evolution. The modern sweet flavor we enjoy depends on the Tas1r2 gene, which first evolved about 450 million years ago: from the ancient Tas1r gene family. From there, evolution did its thing.

Take cats and dogs. Put candy in front of a cat, no thanks says the cat. A dog? Yes please. Slurp. Cats, dogs, and other mammalian predators descended from ancestors with a functional Tas1r2 gene. But several meat-eating lineages independently lost their ability to detect sweetness. Think about it: if your descendants eat animals, a taste for sweetness has little advantage. Picture a complex combination of scent and taste receptors, genes, and other evolutionary tweaks. Traits taking shape multiple times over many generations. And that makes sense.

Now, take birds. Birds descend from the T. rex theropod line of dinosaurs. Somewhere along that lineage, the Tas1r2 gene was lost.

Here’s where the story gets good.

Take hummingbirds. These dinosaurs love sugar. So, did they “fix” their Tas1r2 gene? No! While it’s possible to regain lost capabilities, evolution can find other paths. Life finds its way.

Hummingbirds rediscovered sweetness and opened up a new ecological opportunity: feeding on energy-rich flower nectar. By about 22 million years ago, the ancestorial hummingbird line changed how their savory taste receptors worked, specifically the proteins produced by their Tas1r1 and Tas1r3 genes. That’s a clean example of convergent evolution. Scientists have even reconstructed that receptor, and it responds to sugar! And, the reconstructed one from a 42 million year ago ancestor with swifts, does not respond to sugar! Now that’s evidence.

Think about it. An ancient gene. Several evolutionary branches lost or tweaked sweetness. One branch even found another path to enjoying sweetness. So many ways to cross check the details of evolution.