Where Do Babies Come From? Find the Answer and More in Coming to Life

Coming to Life: How Genes Drive Development

by Christiane Nüsslein-Volhard

Kales Press: 2006. 176 pages.

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If you examine yourself in the mirror, take a closer look at your favorite pet, or even contemplate that pesky fly that just won't leave you alone, it's difficult to not come away with a starry-eyed appreciation for life. With their overwhelming complexity and astonishing consistency, but seemingly endless diversity, these everyday animals are almost enough to make you believe in God. And, I don't just mean some vague modern spiritual presence. No, I'm talking about a hardcore old-school hands-on God, micromanaging the growth and development of each new organism on this Earth, making sure mice beget mice, and no human is surprised in the delivery room with a brand new pet kangaroo.

Of course, thanks to the progress of science we can do a little better than that, explaining the course of development at the cellular and molecular level from conception to birth and beyond. Nowhere is this more apparent than in Nobel Laureate Christiane Nüsslein-Volhard's Coming to Life: How Genes Drive Development, an understated primer that lays out the current state of the art of developmental biology, shocking the reader with just how much we know about how each one of us came to take our unique but fundamentally similar shapes.

Nüsslein-Volhard is as qualified as anyone to write on this subject, having received a share of the 1995 Nobel Prize in Physiology or Medicine for her work with Eric F. Wieschaus in identifying key genes involved in the early development of the fruit fly Drosophila. Their findings, and the systematic approach they developed along the way, impacted developmental biology in a fundamental way. Now, Nüsslein-Volhard is taking a step toward the much fuzzier arena of public understanding of science, in offering up her own version of a primer in developmental biology. She knows what she's talking about, so we probably ought to pay attention.

The book's ten chapters cover the full scope of developmental biology. Starting with basic biochemical and genetic principles and using them to explain how a fly becomes a fly, Coming to Life works its way up the biological ladder eventually providing detailed instructions on to build a vertebrate (unfortunately we'll have to leave that to job to genes and their proteinaceous products: your standard workshop won't be properly equipped for the job). Nüsslein-Volhard then offers a chapter devoted to the specifics of human development, although its brevity will probably leave the reader wishing for more. After pulling things together in an evolutionary context, she closes by addressing a few related hot topics, including stem cell research.

I found Chapter V ("Molecular Prepatterns") particularly interesting. Its discussion of morphogenic gradients, a topic introduced in the previous chapter, is nothing short of fascinating, and may be one of the most effective presentations of the molecular basis of life that I have come across. A fertilized egg looks nothing like a human (it doesn't look like much of anything, really). Starting with just the instructions encoded in a few linear strands of DNA, how then are we able to pop out one human after another, each with the same basic body plan and why, for instance don't we have legs where our arms should be?

That's really a bit of a trick question, because the genes of an embryo don't act in isolation. In fact, the fertilized egg requires a series of complex signals from its mother to kick start its development before its own genetic program can take over. In Coming to Live, this concept is introduced in the model organism Drosophila. Much of the book focuses on the fruit fly Drosophila, since so much of our understanding of this area has come from research on it, including Nüsslein-Volhard's work. Before the fly egg is fertilized, its mother has already deposited a few of her own gene products at strategic positions in the egg. From each nexus a gradient forms, with the highest concentrations closest to the point of origin. Cell nuclei of the growing embryo located within a threshold concentration will be induced to express certain proteins from their own genes. Nuclei below the threshold will express other proteins. This creates new gradients, which activate or deactivate their own sets of targets in neighboring nuclei. (In the early fly embryo, nuclei divide, but cells don't, so this process actually takes place in one big cell containing many nuclei. Cell division occurs later, forming normal cells, each with a single nucleus).

As development continues, broader gradients of gene expression continue to give rise to newer and more refined gradients, dividing the embryo into segments and the location of its various structures. Before the embryo even begins to visibly take shape, its basic body plan is already set in stone. This same process, with subtle differences, operates throughout the animal kingdom, from flies to humans.

Offering a series of revelations such as these, Coming to Life covers the basics of the entire field of developmental biology in a direct and unembellished matter. In fact, it could be viewed as a textbook for a watered-down course in developmental biology for non-experts. Unfortunately, though, and along those same lines, it reads like a textbook at times, delivering fact after fact without excessive commentary or literary flourishes. This prevents it from ever truly coming to life itself. However, it is infinitely more readable (and interesting) than any textbook I've ever struggled through, and Nüsslein-Volhard's own hand-drawn illustrations--found throughout the book--also add a bit of flair. The shear fact that Nüsslein-Volhard was able to summarize an entire discipline's knowledge in a remarkably small space (only 145 pages of actual text) is an achievement in itself. This, coupled with the finding that it is exceedingly understandable and informative, makes Coming to Life a worthwhile read.

Unlike a dry biology textbook, though, Nüsslein-Volhard concludes with a lucid and informed discussion on a variety of "current topics" related to the field, including cloning, designer babies, and embryonic stem cells. The discussion of the latter is particularly relevant today, since President Bush recently vetoed the Stem Cell Research Enhancement Act in July. Nüsslein-Volhard notes that policies on human embryonic stem cell research vary widely worldwide, and many are based on the ill-conceived notion of life beginning at conception. Instead, she argues that implantation of the embryo in the uterus marks a much starker developmental landmark (a previously independently developing embryo suddenly "placing itself in direct and immediate cell contact with another individual"), and without this step, embryonic development cannot proceed. Although life is a continuous cycle--making any definition of the "beginning of life" fundamentally flawed--since the derivation of stem cells from an embryo takes place before implantation, this should prove the "moral concerns" (a.k.a. political pandering) guiding current policy unfounded.

It should go without saying (and it's not spelled out directly in the book), that the information presented in Coming to Life overwhelmingly demonstrates the need for continued animal research. As Nüsslein-Volhard herself points out, "As none of these methods can be applied to humans, human gene function must be largely inferred from research on model organisms." Although much can be learned from fly research, studies on other mammals are essential for working out developmental details in humans.

The question that a comprehensive book review should answer, explicitly or not, is whether anyone should read this book, and if so, who? I would argue that Coming to Life is a worthwhile read, but probably not for everyone. However, it is a must for two groups in particular: (1) non-experts wishing to understand the basics of developmental biology or those with a burning desire to further understand the molecular basis of life in general and (2) policy makers.

The former group should find reading Coming to Life particularly enjoyable and informative. Those without a background in the biological sciences might struggle at times, however. Although Coming to Life begins with a general introduction, it's certainly not sufficient for the neophyte, and the book at times resorts to terminology that scientists take for granted but others wouldn't be familiar with. On the other hand, those of us in the biological sciences may find that the introduction tends to drag on much too long. Writing popular science is difficult for that reason, having to strike a balance between giving the reader the proper background and not being overly pedantic (and putting scientist readers to sleep). Either way, once the book really picked up for me when the introductory material ended (starting with Chapter IV), and there were certainly no regrets from that point on.

Unfortunately, policy makers might not be so eager to read Coming to Life, even though nobody would benefit from it more than them. The policy implications aren't spelled out explicitly until the final chapter, although the rest of the book gives the reader the background to understand the reasoning behind these and judge for him or herself. For those in power who are making such important science policy decisions day to day, this understanding is critical. I'm not going to kid myself, though, and I certainly don't expect every member of the Senate to read this book (or even just President Bush).

But, it would be nice. I guess I'll just keep dreaming.

Update: Check out the other reviews at Pharyngula, Evolgen, A Blog Around the Clock, Retrospectacle, Adventures in Ethics and Science, and Gene Expression.