How the Octopus Broke the Rules and Got So Smart

Apr 18, 2017

There's a textbook version of evolution that goes something like this: random changes to an individual's DNA are inherited by its offspring. The worst changes are weeded out by natural selection, and the process goes on. Unless you're an octopus or a squid.

New research suggests that cephalopods do something different. They change their RNA. A lot. And that may help explain why they, alone amongst all invertebrates, are so intelligent.

To understand the difference, imagine your DNA, or genome, as a cookbook - the cookbook - that contains a recipe (a.k.a. gene) for every dish you'll ever need. Your version of pasta primavera may be subtly different from your neighbors, but you all have a recipe - one that has been honed by generations of trial and error. 

Here's the trick: your cookbook can't go into the kitchen. Instead, each time you want to use a recipe, you have to make a copy of it. For most cooks, it's important to make an exact copy, to avoid ruining the recipe. But, a master chef might be able to edit the recipe a dozen different ways, all of which turn out wonderfully. Cephalopods are those rare master chefs.

In cellular terms, a gene has to be copied from DNA (which is stuck in the nucleus) into RNA, which can, in turn, be translated into the proteins that actually do the work of the cell. For most animals, ensuring that the DNA is copied into RNA faithfully is extremely important, and RNA editing is relatively uncommon. For cephalopods, the exact opposite is true; they are prolific RNA editors. 

That means they can produce a much larger variety of proteins. This seems to be particularly true for the very genes and proteins that build their nervous system and transmit signals from nerve to nerve. And that may explain how cephalopods, whose cousins include clams and snails, got to be so smart.

Guest: Joshua Rosenthal, senior scientist at the Marine Biological Laboratory in Woods Hole, MA