A bird biologist spent two decades trying to solve the mystery of a kind of finch, but a dog and wolf biologist just figured it out.
Some black-bellied seedcrackers, a kind of Cameroonian finch, have small beaks, while others have large ones. Tom Smith, a UCLA biologist who studies birds, was so intrigued by this difference that he spent two decades trying to understand it, even keeping a finch colony for study.
He was halfway there: he learned that finch beak sizes worked pretty much the way you'd learn in high school genetics, if you remember drawing Mendelian Punnett squares. Small-beaked parent finches can only make small-beaked babies, the same way blond human parents can only make blond human babies. That's because small-beaked finches had two recessive alleles, while big-beaked finches have a dominant, big beak allele or two thrown in.And Smith knew there was a connection between food and beaks. Big-beaked finches tend to eat larger seeds, while small-beaked finches eat smaller seeds. (No shocker there.)
The mystery was in the DNA. Smith had no idea what genes created these beaks sizes. So he brought in an unexpected ally: Bridgett vonHoldt, a Princeton biologist who studies dogs and wolves, not birds. When she compared small-beaked finch DNA to large-beaked finch DNA, she noticed one spot where the genes were different: a set of 300,000 base pairs. Right in the middle of that chunk was something that she saw in dogs: gene IGF-1.
Gene IGF-1 is a pretty awesome gene.
"In dogs, this is a giant gene, literally and figuratively," vonHoldt said. "It's a growth-factor gene. In dogs, if you change how it's expressed, with just a few genetic changes you can change a normal-sized dog into a dwarfed, teacup-sized dog."
Depending on where you find it in the DNA, it can make an animal's body part bigger, or it can make the whole animal bigger.
"If this gene is expressed more, you expect a larger trait: a larger body, a larger foot, a larger ear, whatever it is controlling. It then is easy to imagine that with a small change to this gene, traits could very easily change in size or shape. We suspect this is the story here, with these beaks," vonHoldt said.
So the same gene that can give a finch a large beak can make a Doberman fit in your purse. It's almost like animals are stories written with different combinations of the same sentences. And thanks to DNA, we already know the sentences are written with the same letters. We're all made of the same stuff.