Evo Devo is evolutionary development biology, the third revolution in evolutionary biology. The first was marked by the publication of The Origin of Spec ies. The second occurred in the early 20th century, when Darwin's theories were merged with the study of genetics. Now the insights of Evo Devo are astonishing the biology world by showing how the endless forms of animals - butterflies and zebras, trilobites and dinosaurs, apes and humans - are made and evolved. Perhaps the most surprising finding of Evo Devo is the discovery that a small number of primitive genes led to the formation of fundamental organs and appendages in all animal forms. The gene that causes humans to form arms and legs is the same gene that causes birds and insects to form wings, and fish to form fins. Similarly, one ancient gene has led to the creation of eyes across the animal kingdom. Changes in the way this ancient toolkit of genes is used have created all the diversity that surrounds us. Sean Carroll is the ideal author to lead the curious on this intellectual adventure. He is the acknowledged leader of the field, and his seminal discoveries have been featured in Time and the New York Times.
What most recommends this book is the author’s enthusiasm for his topic. Through his perspective, I thought about how incredible it is that a single cell can become a whole organism and how strange it is that the DNA shared by all organisms is so similar, yet encodes instructions for so many different creatures. As someone in a different field, I did think it was a bit presumptuous for him to declare understanding of this process the “holy grail of biology”. Also, by the time I started undergrad, a lot of the “new” research he describes was being taught in the classroom. For instance, that fact that most of the genome is non-coding and that a lot of the differences between species are caused by regulatory regions is genetics 101 these days.
My least favorite part of this book was the wordiness. Especially when describing the basics, the author came across as very pedantic. And he almost always included more detail than even I, another biologist, cared about (lists of gene names for example). I do think the book would fell less wordy to someone with less of a biology background, but most other reviews I’ve looked at also said the book could have been condensed a lot. Unfortunately, the excessive length made it harder to focus on the cool facts and as a result, the book felt kind of dry to me. To be fair, I have been a little more in the mood for fiction lately, but it’s also true that really good non-fiction can usually pull me in anyway.
A very lucid discussion on how changes in animal morphology can come around just by changes in timing, spatial distribution and "dose" of genes, switches and modifiers helps in really unifying the understanding of DNA activity, macroscopic morphology and evolution. I really think if you don't understand evolution of form after reading this book, there are some basic problems with accepting reasoned arguments. Brilliant!
He details the emergence of the body axes under the Hox proteins and how they work to isolate the expression of genes to promote modularity. Isolation makes regional use of bone, collagen, epithelium etc independent of other modules that also use the same genes. This allows constant tinkering without pleiotropic disruption.
The final result is:
1 Hox mapping regulation proteins. Body axis planers.
2 Master body specializing regulators. Eye, limb bud, heart. Look up Pax6, Dll, Tinman for examples of DNA binding regulatory proteins.
3 Regulators at the cell level to keep the life process going. Cellular housekeeping genes
1 - reuse what is already there – modify preexisting systems.
2 – multifunctionality & redundancy. If the systems do overlapping jobs there is space to separate and specialize. Division of labor => niche adaptation
3 – modularity to allow modification of isolated regions independent of other modules that also use the same genes.
Modular architecture - Isolate the control to the geographic position.
Master genes for mapping and local master organizers- expressed homeobox proteins
The physical geography
Complex DNA regulatory patterns to provide regulatory combinations of switch settings. Allows reuse in time and specify cell type expression.
This one combines well with "Your Inner Fish"
Caroll lays out beautifully what he and colleagues are learning through combining embryology with evolution, and shows how the union solves a number of mysteries that have been puzzling scientists for decades.
Although this is very definitely a layman's introduction, it does get quite deep into the science, to the point that I found myself a bit confused by all the different concepts - switches, toolkits, etc.
I also couldn't help feeling that he allows his enthusiasm - and his bias as one of the leaders in the field - to get the better of him, leaving the impression that not only is evo-devo the best thing since sliced bread, but that no-one had ever made any progress in studying evolution until it came along.
Pity, because the science clearly has had a major impact, but there's still plenty of interesting things going on outside of the field and Carroll doesn't do himself any favours by implying otherwise.
As the first pop book of its kind (at least the first I know of) I applaud the author's sentiments.
For the first half, focussed on embryology, I think he did a pretty good job.
Sadly I found the second half, focussed on evolution, frustrating because it lacks the details and mechanisms of the first half; I'm not sure if this is because the science is not yet worked out or if the author simply doesn't care as much about this area.
There are few very nice ideas that it explains well. For example,
* The same tool kit proteins are used to guide development across all sorts of animals, and portions of it predate the Cambrian explosion. Changes in control switches and "circuits" (combinations of switches) in the DNA modify how these proteins are used. There is strong pressure to leave the homeotic (Hox) genes the same, though.
* Complexity in form is often enabled by duplication of modular structures, followed by specialization. (A perfect example are the many specialized structures in arthropods.) For this reason, the same tool kit proteins to place many structures that now seem quite different. One can guess that without modular structures, allowing for this kind of evolution, animals could not have been so successful.