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For over a century, opening the black box of embryonic development was the holy grail of biology. Evo Devo -- Evolutionary Developmental Biology -- is the new science that has finally cracked open the box. Within the pages of his rich and riveting book, Sean B. Carroll explains how we are discovering that complex life is ironically much simpler than anyone ever expected. 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 tool kit 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.… (more)
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The author gives an introduction to DNA and proteins and then builds up to what Hox genes are and how they work with other proteins to form a genetic tool kit (hormones, cell-type regulators, signaling proteins, Hox proteins, etc.). He shows how the tool kit determines the physical characteristics of many animals, including the size and placement of butterfly wing stripes and spots. In fact many of the specialized organs (lungs, wings, the spider’s spinneret) are modifications to the basic appendage.
The author’s excitement shows throughout the book and he excels at making some of the more complicated ideas understandable. The book has beautiful color plates of protein expression in embryos and butterfly wings. The ”Further Reading” section at the end was nicely done and not just a quick afterthought. If you have a biology background you will probably be familiar with large parts of this book. There were several areas where I would have liked the author to go deeper, but each book has an audience and this book does a great job at the level its aimed at.
Some quotes:
“But the building of an entire animal is complicated. The complexity arises from the parallel and sequential action of tool kit genes – dozens of genes acting at the same time and place, many more genes acting in sequence as development progresses. The chain of parallel and successive operations is what builds complexity” pg. 106
“It is a small leap from understanding how switches control development to anticipating how they have shaped evolution. Switches enable the same tool kit genes to be used differently in different animals. Because individual switches are independent information-processing units, evolutionary changes in one switch of a tool kit gene or in a switch controlled by a tool kit protein can alter the development of one structure or pattern without altering other structures or patterns. This is the key to the evolution of modular bodies and body parts…” pg. 131
“…everything about a tool kit protein’s action depends on context. Distal-less carries out its limb-building role in specific places and times; its job in the wing spots is in another place and time. And controls an altogether different pattern.” Pg. 208
“Evo Devo has revealed the continuity among forms that was masked or about which there were uncertainties based on appearance alone. By revealing the developmental similarities among structures, Evo Devo presents a wholly new kind of evidence that is far more objective than morphology alone.” Pg. 288
He details the emergence of the body axes under the Hox proteins and how they
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"
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
As the first pop
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.
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
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.
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.