Over the past several decades, paleontologists—including [Jack] Horner—have found ample evidence to prove that modern birds are the descendants of dinosaurs, everything from the way they lay eggs in nests to the details of their bone anatomy. In fact, there are so many similarities that most scientists now agree that birds actually are dinosaurs, most closely related to two-legged meat-eating theropods like Tyrannosaurus rex and velociraptor.That's funny. Here's where the Jurassic Park comes in:
But “closely related” means something different to evolutionary biologists than it does to, say, the people who write incest laws. It’s all relative: Human beings are almost indistinguishable, genetically speaking, from chimpanzees, but at that scale we’re also pretty hard to tell apart from, say, bats.
These regulatory genes—the master switches of development—contain the recipes for making certain proteins that stick to different stretches of the genome, where they function like brake shoes, controlling at what time during development, and in what part of the body, other genes (for things like growth-factor proteins or actual structural elements) get turned on. The same basic molecular components get deployed to make the six-legged architecture of an insect or fish fins or elephant trunks. Different body shapes aren’t the result of different genes, though genetic makeup certainly plays a role in evolution. They’re the result of different uses of genes during development. So making a chicken egg hatch a baby dinosaur should really just be an issue of erasing what evolution has done to make a chicken. “There are 25 years of developmental biology underlying the work that makes Horner’s thought experiment possible,” says Carroll, now a molecular biologist at the University of Wisconsin-Madison. Every cell of a turkey carries the blueprints for making a tyrannosaurus, but the way the plans get read changes over time as the species evolves.That is one of the best definitions of hox genes that I have ever seen. The problem is that you are looking at a developmental level that is very basic. It will be interesting to see how this is applied in the next few years.