The Study of Racialism

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Sean B. Carroll, Endless Forms Most Beautiful: The New Science of Evo Devo (New York: W.W. Norton, 2005)

I first became interested in Evo-Devo (evolutionary developmental biology) about 20 years ago when a Scientific American article on embryology described cell transplantation across species.

I can no longer recall the two species in the article. They may have been frog and salamander. What caught my eye was that if you take from a frog embryo cells that are destined to become the frog’s toe, and transplant them to a salamander embryo where an eye should grow, those cells develop into a frog’s eye (not a frog’s toe nor a salamander’s eye).

The implications were stunning. That frog cells develop into frog stuff is trivial. Frogginess is all that frog cells know how to do, after all. But that the transplanted cells develop into an eye (although taken from the frog’s toe region) means that: (1) Every embryonic cell has the ability to become anything, depending solely on its latitude-longitude position on the embryo. Okay. I can grasp that: stem cells and all that. But (2) the GPS signal that tells a cell its latitude-longitude position on the embryo is common to different species. (To all animals, it turns out.) That fact just blew me away.

We now know that humans have about 25-30 thousand genes that encode for proteins. Virtually all of our genes are common to all mammals, and most are common to all animals (even insects). Consider the FOXP2 gene. When defective, it prevents a baby bird from learning its species’ song, and it stops a human infant from learning to speak. Another example, the same version of a gene that produces fish with too many rays in their fins, produces people with six or seven fingers or toes.

It turns out that less than 2 percent of our DNA comprises genes that encode for proteins. A bit more than that amount comprises switches that control those genes. The DNA switches turn genes on and off, delay or accelerate their action, and strengthen or weaken the genes at different points in time. And they exert this control depending on what stage the developing embryo is at and, most important, depending on where on the embryo the particular cell is located.

That most of our genes predate the Cambrian explosion (before even arthropods were invented) is startling. That most of the switches are equally old is shocking. The only difference between me and a fruit fly is in the timing of those DNA switches.

Many scientists believe that the findings of Evo-Devo are revolutionizing biology today as deeply as Darwin’s discovery of natural selection did, or as Watson, Crick, and Franklin’s discovery of the DNA molecule did years ago.

For a fast-moving accessible explanation of Evo-Devo, I recommend this book.

sagascend · Moderator Joined: 17 Jun 2006 {Posts: 2302 }

Wow!!!! Thanks for posting. I'm adding this to my list of books to read.