Grow a Backbone

Did we get our backbones from animals like this?Lately I have been reading a book by Jeffrey Schwartz called Sudden Origins. In it Dr. Schwartz talks about the idea that species are not made gradually but instead just suddenly appear (in geological time anyway).

Reading the book was a bit like panning for gold. It was hard work and I needed to sift through a lot of silt but every now and then I got a nugget of gold. One such nugget was about where backbones may have come from.

Hundreds of millions of years ago, there was a time when no animals had backbones. These animals also weren't bilaterally symmetrical. This just means that their bodies weren't set up as two sided (think right and left halves of a human). Instead, they were more like sponges and starfish.

So how do you get from a starfish to a regular old fish? Seems like you'd need to make an awful lot of changes. You would-- unless you were looking at the larval forms of some of these animals.

Some modern creatures that just sit on the bottom of the sea have a larval form that moves around. This is useful in setting up distant colonies.

What is interesting is that some of these larvae have bilateral symmetry-- they have a right and a left side. And some of them even have the beginnings of a notochord on their back! So all we would need to do is somehow freeze the beast at the larval stage and you're halfway to something with a backbone.

Basically then, we need for the larva to sexually mature before it physically does. This sounds like a toughie but it isn't as hard as you might think. It is common enough that scientists even have one of their awful names for it-- neoteny.

The classic example is the axolotl salamander. This animal usually stays a tadpole throughout its life-- it never makes it to the salamander stage. But it still lays eggs. And when those eggs hatch, they give rise to more salamanders that will become sexually mature as tadpoles.

This sort of thing is pretty common with salamanders. But it may have happened in a lot of other cases as well. Other possible examples include dogs, who act like wolf puppies. And some relatively hairless and flat faced chimps (you and me).

And maybe even an ancient larva of some sea squirt-like thing lying on the ocean floor. How cool is it that we may all be descended from a juvenile sea squirt?

Dr. Barry Starr is a Geneticist-in-Residence at The Tech Museum of Innovation in San Jose, CA.