Monday, July 03, 2006

Review of "Endless Forms Most Beautiful"

I love good popular science books, but I’ve noticed that good books about molecular/cellular biology are relatively rare. (When I say molecular biology, I don’t just mean traditional molecular biology - I mean biochemistry, biophysics, molecular genetics, genomics, cell biology, and anything else that frequently gets lumped under the term ‘biomedical research’ - I don’t like this term, because it suggests that this research is mainly applied science with a medical goal, and not basic research on fundamental questions.)

Physics books seem to dominate the shelves at Borders. There are a ton of great physics books from writers like James Gleick, Richard Rhodes, Brian Greene, Roger Penrose, Peter Galison, Richard Feynman, etc, etc. If you’re interested in biology, the best books tend to be dominated by more traditional evolutionary biology - books by Ernst Mayr and Stephen Jay Gould, and even Richard Dawkins come to mind. Their books are engaging, but far removed from the molecular biology most biologists are engaged in. This is an especially egregious problem with Mayr’s books. One of his last books, What Evolution Is really gives a distorted picture of evolutionary biology today because of its neglect and superficial treatment of molecular evolution. Mayr never became that familiar with the basic research in this area. (Who could blame him - the guy was in his 80’s when PCR was invented.)

Over the last five years, popular science books on molecular biology have started to show up more frequently, but rarely are they as good as the books written by the writers I mentioned above. One book that actually is up to par recently came out in paperback - Sean Carroll’s Endless Forms Most Beautiful, which is a great introduction to the latest in the field of Evo Devo (evolution and developmental biology). Carroll is a mainstream, active researcher in his field, and a Howard Hughes Medical Institute Investigator (which is a fairly prestigious position).

The basics:
The first part of the book covers material that is relevant to a huge chunk of research in basic biology. Carroll introduces transcription factors (proteins that bind to specific segments of DNA and influence whether a neighboring gene is turned on or off) and the DNA elements they bind to, which are essentially genetic switches. He also introduces the types of experiments you can do with the fruit fly Drosophila melanogaster, which is an extremely important model organism not just in Evo Devo, but in many other fields as well. The regulation of gene expression through interaction of transcription factors and the short DNA motifs is a very active area of research, one which has received a big boost from genome sequencing projects and newly developed computational tools. General readers who follow Carroll’s overview will be well-prepared to understand the general picture of a lot of basic research today.

Evo Devo:
As Carroll says, Evo Devo is certainly an exciting field. Master regulator genes that existed more than 500 million years ago have been recruited over the course of evolution to control the development of arms, antennae, fins, fly wings, and butterfly wing patterns (to name a few). How revolutionary this finding was hadn’t quite hit me before I read Carroll’s quote of Ernst Mayr, who said that homology wouldn’t be very useful in molecular biology because DNA sequence would have changed too much between species for us to detect significant similarities. Instead, we have found genes that have been preserved and modified through evolution to produce much of the remarkable biodiversity we see today. Evolution and molecular biology have reinforced each other to a degree that nobody really anticipated 30 years ago.

Much of the book is devoted to insect development, which is appropriate because that is where we have been able to learn the most about the role of developmental genes in the evolution of diverse forms. We can do experiments in insects that we can’t do (ethically, or sometimes technically) in mammals. However, Carroll does tackle mammals in the last few sections of his book. He devotes a chapter to human evolution, and discusses some of the genetic changes that might have played important roles. In this discussion he brings up an extremely important point - one which is solidly accepted by probably the majority of molecular biologists, even though it once was hotly debated by more traditional evolutionary biologists: no individual genetic change is THE key to the evolution of a new trait, like wings, or larger brains, or specialized appendages like antennae. Evolution proceeds through multiple small genetic changes that impact a variety of traits - macroevolution is just lots of microevolution of the sort we can find and test in the lab. (The geological analog of this argument is that the Grand Canyon was produced through the mundane forces of sedimentation and erosion that we observe today - we don’t need to invoke some cataclysmic force.) This is a major lesson to come out of Evo Devo, and I think the alternative view is strongly excluded by what we know about molecular genetics.

The larger societal picture:
Carroll reprints some fan mail he received after one of his papers was covered in the media:

“It’s a shame that you brains can’t get together to help solve the earth’s problems instead of using your God-given talents and our TAX money to figure out the genes that color butterfly wings - who cares?!”

Leaving aside the fact that much of Carroll’s funding does not come from tax money (as I mentioned, he gets funding from the Howard Hughes Medical Institute, a private foundation), the letter writer is absolutely clueless about the scientific aims of this work.

Carroll and his colleagues are not out to merely “figure out the genes that color butterfly wings”. It’s clear that the letter writer has a view of genetics that most of the public probably has - there is a gene for X, and a gene for Y, and yet another gene for Z, and scientists should give priority to figuring out these genes ‘for’ important traits in human beings and not butterflies.

This view of genetics is absolutely wrong.

What Carroll is really after is figuring out how genes work. The butterfly research helps us to better understand how patterns of interacting genes control cellular processes to produce an adaptive trait. And we’re not just learning a lot about how evolution produces new features; we’re learning how genes operate to produce complex organisms like us. If we ever want to figure out how to repair genetic diseases or regenerate neural tissue, we have to understand at a fundamental level how genes produce traits. It is extremely difficult to do this in humans, so why not do it in butterflies?

Carroll makes one last point about the relationship of Evo Devo to society at large: opposition to evolution is insane. Molecular biology is deepening our understanding of evolution in an unprecedented way, and it is impossible to separate research studying evolution from research teaching us how our own biology works.

No comments: