Endless Forms Most Beautiful: The New Science of Evo Devo and the Making of the Animal Kingdom [Englisch] [Taschenbuch]

Classical experimental and comparative embryology is a field that has fallen on hard times until recently. When I attended the University of Arizona there was a full blown course in embryology, both descriptive and experimental. By the time I was a graduate student at the same institution the course had been rolled into Organismic Biology in which all of embryology was loaded into a third of a semester. In essence developmental biology in relation to evolutionary studies gave way to molecular. Still some pretty good work went on in the background that impinged on development and was to result in the discovery of HOX genes. HOX genes (or homeotic genes) proved to be the "organizer" that was postulated by various experimental embryologists such as Spemann. Even more astoundingly they proved to be pretty much the same, no matter which organism was being studied. HOX genes in humans were essentially identical to those of insects!

This remarkable fact offers proof for the idea that all life is related and that development is a key factor in evolution. In "Endless Forms Most Beautiful" Sean B. Carroll explains the significance of such discoveries as the genetic "tool kit" (including HOX genes) on our understanding of evolution and of development. Indeed, this is a fascinating story that has already caused me to rethink some of my understanding of evolutionary principles.

We live in an amazing world in an amazing universe. The genetic material made up of DNA is a very remarkable material. What other materials could have developed huge numbers of organisms (as many as 30 million extant) that vary from zebras to sulfur bacteria? Yet that complexity appears to have developed from a very simple beginning.

Carroll was influenced by Steven J. Gould in his interest in biology, but he does not flinch from disagreeing with Gould about contingency. Carroll says that if the tape of evolution were run again, pretty much the same thing would have happened. I think that I may have to agree to a point (although not as far as Simon Conway Morris goes with it). However, certain alterations in earth history might still have caused a radical change in the outcome, as in the development of a completely water covered planet or a very large asteroid strike (larger that the one that apparently killed the dinosaurs except birds). At the same time not all evolved faunas that developed in isolation from each other resemble each other exactly. The marsupials of Australia, for example, had a number of forms similar to placental mammals. However, there was no exact analog to the kangaroo outside of Australia or of hoofed animals in Australia (giant wombats don't have hooves). I agree faunas can be similar, but not necessarily identical and that intelligent life may be inevitable, but may not necessarily have looked like us or even evolved from mammals.

That said, evo-devo, as the evolutionary development researchers call it, has much to offer and it certainly cannot be dismissed. This is an exciting time to be involved with evolutionary biology, despite the creationist (or more sophisticated "Intelligent Design") attack on the whole idea.

This is an excellent introduction to the excitement of a continuing unfolding of evolutionary thought. I recommend it highly.

Ever since high school I've been looking for ways to branch out my fascination and interest from physics to biology. I have read the books and collections of essays by Stephen Gould and loved them, but nothing else has so caught my attention until THIS book.

Sean B. Carroll (there's more than one Sean Carroll out there) does a fine job showing how insect and vertebrate forms are built. More than that, he shows how they are fundamentally related WAY back in the past. Even more controversial than humans being related to chimps, we're related to, say..., lobsters!

What's cool is these conclusions are based on repeatable experimental evidence of the makeup of DNA, genes, chromosomes etc. Carroll makes a nice analogy between the vast amount of DNA strands that are NOT expressed in individual forms and the vast amount of matter in the universe that is NOT expressed as visible stars and galaxies. (OK, so maybe I STILL like physics a little more, but I'm making progress!)

Carroll nicely acknowledges Gould's contributions to the popularization of better public understanding of evolution (e.g., Wonderful Life) and further extends the discussion of Darwin. Trying to understand life without evolution is like trying to understand the universe without gravity. But Carroll moves the discussion from anecdotes to evidence. I like that!

I hope to see MUCH more on this new field of evolutionary developmental biology. As much as I am interested in how the universe began (and where it's going), I am interested in how human beings began and where THEY might be going.

Despite vast differences in form and function common principles coordinate animal development from a single fertilized egg. Master genes that control development are found across widely divergent species - Drosophila fruit flies and humans share a deep genetic legacy - many of the genes identified as controllers of vertebrate development were originally discovered in these flies.

Multicellular plants and animals are essentially societies of cells that vary in configuration and complexity. Darwinian evolution shaped these multitudinous forms as a result of small changes in offspring and natural selection of those best adapted to their environment. Variation arises from mutations in genes that control how cells in developing embryos behave. This tight linkage between evolution and development lies at the heart of the questions evo devo, shorthand for evolutionary developmental biology, is attempting to answer. Sean B. Carroll is perfectly positioned to explain evo devo, and his comprehensive understanding illuminates "Endless Forms Most Beautiful" The New Science of Evo Devo and the Making of the Animal Kingdom."

When and where genes are expressed determines how animals develop. The control regions of these genes - switches that change existing patterns of gene activity into new patterns - are crucial and a single gene can have many control regions. This flexibility underlies the fact that 95% of genes coding for proteins are similar in humans and mice. Evolution of control regions has made us human - and different from our primate ancestors.

Drosophila is utilized to explain the basic developmental tool kit shared by all animals. Carroll introduces the master Hox genes and intercellular signaling molecules such as proteins specified by hedgehog genes. The economy of signaling proteins utilized during development is also emphasized - the same molecules can be employed multiple times since cells respond differently according to their genetic characteristics and developmental history. Carroll also illustrates how individual animals are made up of similar parts - modular construction plays an important role in evolution. Structures ranging from vertebrae to spots on butterfly wings are artfully presented to drive this point home.

Complex animals arose in the Vendian period (650 - 543 MYA). During the Cambrian (543 - 490 MYA) animals with hard body parts enter the fossil record. Evo devo shows that genes responsible for Cambrian animals were plausibly derived from Vendian precursors. Cambrian arthropod dominance is probably due to Hox genes that specify different body segments and the corresponding appendages that formed their bodies. Carroll explores how the number of distinct appendage types increased - the relative shifting of Hox genes could have lead to the ancestral biramous (forked) limb that eventually diversified into structures ranging from gills to wings.

Butterfly spots are a beautiful and clever example of evolutionary tinkering. Each spot appears to evolve its shape, color and size independently of other elements. Evolution has tinkered not only with the qualities of each spot, but with the making of the spot itself. Carroll's group discovered that at the center of each spot the gene Distal-less - a key gene controlling the distal development of appendages such as insect limbs - is expressed and initiates spot development.

Carroll also addresses creationists - the bizarre bibliolaters who think Flintstones reruns on late night TV are documentaries - by pointing out the importance of evolution and evo devo to science and human knowledge in general. The PR campaign known as Intelligent Design is similarly debunked as irreducibly insipid. Science is full of mysteries, that is why there are still employment opportunities for scientists.

After reading this important book try From DNA to Diversity: Molecular Genetics and the Evolution of Animal Design by Sean B. Carroll, Grenier, and Weatherby for a more detailed discussion or The Plausibility of Life: Resolving Darwin's Dilemma by Kirschner and Gerhart - who introduce "facilitated variation" based on evo devo insights to explain the evolution of complexity and novelty.