Sonic Hedgehog!! (A Summary of Ch. 3 of Your Inner Fish)

Would you believe it if I told you that every animal is somehow related to each other?

Well, it's sort of true, and scientists are still figuring out a lot of really important chunks of that theory, but most discoveries of genetic similarities between different species are very recent, like 90's recent. Now, I don't know what you looked like back then, but I couldn't eat my food without it drooling down my chin back in the 90's.

Neal Shubin's (the guy who wrote Your Inner Fish) coworker, Randy Dahn, wanted to test DNA in sharks. In order to do that, Dahn first needed to understand ZPA tissues. These tissues showed that the relationship between living animals and fossils are based on more than just anatomy. The study of fossils and DNA go hand in hand actually. Shubin even says so when commenting that his research lab was split into two sections: fossils and DNA existing peacefully together in the realm of science.

The second part of Shubin's lab was DNA and the study of embryonic development. According to Shubin, most of our cells have the same copy of DNA.

Also, our limbs exist in three dimensions. Now, you're probably going "What the heck does that mean? We live in a 3D world. Of course we're in 3D." Well, maybe if you'd hold on for a bit, I'd tell you what it means.

Our limbs exist in three dimensions: a top and bottom, a pinky side and a thumb side, and a base and a tip. Our body develops limbs in this certain structure because of the chemicals produced by cells in a developing body. Researchers discovered that a certain portion of cells in the body controlled all limb development. If the cells were removed, all limb development would stop. If you cut the patch of cells in half, two limbs would develop.

Scientists had tested this hypothesis on chicken eggs and wanted to see if the same would happen to other animals, so they turned their attention to the fruit fly and found the hedgehog. The hedgehog is a gene within the ZPA tissues that control limb development. When scientists discovered the hedgehog in chickens, they rechristened it the Sonic hedgehog (because they saw the chance, and they took it.) The Sonic hedgehog gene could be manipulated by a Vitamin A injection, resulting in the change of how the limb develops.

And that's where Randy Dahn came into play. Dahn wanted to see if the sonic hedgehog was true for even the most different of animals, so he decided to test his theory on shark embryos. And hey, it worked!

Every animal has a sonic hedgehog gene. Every animal obtained their limbs from one animal and then branched out into many many different animals, which brings me back to my first point that we're all sort of related!