Development and Evolution: Developmental Mechanisms of Evolutionary Change

Scientists Speak 25.1

Transcript begins after advertisement.


Dr. Carroll:  So I think the human curiosity about who we are, about our place, drives us to deeper and deeper and deeper questions. And those questions have magnificent answers.


I think perhaps that’s the one aspect that’s most missed when the debate about Darwin, for example, rages, is that Darwin, when he talked about “endless forms most beautiful,” he saw the magnificence in nature, and he saw the magnificence in a natural explanation of how that diversity had unfolded.


Evo-devo is the attempt to understand the evolution of form. And that means the evolution of bodies—their size, their shape, their color, how new parts evolve, how the number of body parts evolves, the real drama of evolution as we see it in things like the fossil record.


I think the first major discovery of evo-devo, the real stunner that no one was prepared for, was the discovery that the genes in fruit flies had counterparts in all animals in the animal kingdom. The expectation prior to that was, well, the recipe, sort of the genetic recipe for making a fruit fly was really distinct. And fruit flies, they don’t have bones and they don’t have big brains, they have, you know hollow legs, and things like this. They’re very different from vertebrates or mammals or apes like us.


And the stunning discovery was that, no, these genes that build fruit fly bodies have exactly the same counterparts in ourselves and in butterflies and elephants and earthworms and all sorts of things. And so we realized that looks are really deceiving. That was the most clear-cut change in thinking, was that looks were leading us in the wrong direction. That really, while anatomy appeared to be different, there were fundamental genetic instructions underling the building of the whole animal kingdom.


Man: So what I think that what we may be overlooking concentrating on the binding sites for abdominal B is their spacing.

Dr. Carroll: Every change in a trait, whether that’s eye color or the invention of an eye or the shape of a limb, every change in traits is due to changes in DNA. And it’s only in the last 20 years that we could track those changes with pinpoint precision.


DNA contains the ultimate forensic record of evolution. Twenty, twenty-five years ago, if you took all of the DNA sequence that biologists had gathered up to that time, and you typed it out on pages, like the pages of a book, you’d have roughly a book about the size of a novel. If you were to type out all of the DNA information we have now and stacked those books, it would be somewhere around eight or ten times the height of the Empire State Building.


This is Kathy Vaccaro, and she’s been working on putting some genes back in fruit flies. And she’s looking for any of those fruit flies that have taken up those genes, because they’re going to have a change in their eye color. So she’s very rapidly screening through these flies to see if any of them have gone from a white-eyed to a red-eyed eye color, and that will tell us that she’s gotten the gene in.


Our access to the DNA record has ushered in a new golden age in evolutionary science. We can do all sorts of things that the great minds of evolutionary science could only have dreamed of and probably didn’t dream of just a few decades ago.

And when we mine the DNA record of an individual species, there are all sorts of things we can learn from that record about how that species came into being. And I think perhaps the most vivid illustration I can think of that is to talk about one of the most peculiar, remarkable animals on the face of the planet. And it’s known as the ice fish.


These fish live in the very cold waters of the Southern Ocean, waters that are around 29 degrees Fahrenheit. The most remarkable thing about the ice fish is that they have no red blood cells at all. The only vertebrates, the only animals with backbones on the planet, that have no red blood cells. And we know that’s because they got rid of red blood cells in the course of evolution. And the signature of that, that we can find, fossilized in their DNA, the remnants of the genes for proteins that make red blood cells red, the hemoglobin gene.


So this fish has in its DNA a record of all sorts of changes that have taken place. And as soon as we inspect that, it tells us so much about how these fish are different from their ancestors, and it gives us so many clues about how they’ve adapted to this very extreme habitat.


What we see at the molecular level, at the anatomical level, is that evolution is a tinkerer, that new things come about usually from combinations of old, preexisting things, and from sort of modifying something that might have had another job into doing a new job.

We see this at many, many levels. In butterflies, for example, genes involved in making spots are genes whose ancestral job was in making limbs. But they’ve pick up a whole other new job in the course of butterfly evolution for decorating the fancy color patterns on the wings.


The message we get again and again and again at the genetic level, is that evolution is not so much a matter of inventing entirely new genes but of using old genes in new ways—like a tinkerer.


So it’s a never ending process. And to quote Darwin, it’s a matter that “endless forms most beautiful” have been and are being evolved as the planet changes. Animals and other species are keeping up with the ever-changing Earth. And those changes in the earth are directly relatable to how living forms have changed. And as long as the earth keeps on changing, and as long as those resources are there, evolution will continue.