Among the prescient thinkers who, halfway through the last century, created the so-called modern synthesis of evolution, natural history, and genetics, Theodosius Dobzhansky summarized it most succinctly: Nothing in biology makes sense without evolution. Sixty-five years later, it is clear evolution makes sense of even more than just biology. Charles Darwin’s insights are applicable to psychology and economics, computer science, Earth sciences, and cosmology.

The modern synthesis proposed that evolution is genetic change, and that genetic change can and does change body plans, heritably: It changes shapes, functions, life history, and behavior. The central assertion of the modern synthesis was that the continuous appearance, over eons, of new types of plants and animals on Earth, was precisely the same process we see happening during humanly comprehensible intervals.

“Morphogenetic” or body-building processes were observed even by Aristotle (in chicken embryos) and described in detail long before Darwin’s time. A contemporary example is the acquisition of resistance by pathogenic microbes to the drugs we so expensively design for killing them. To put it in the usual terms, as does Sean Carroll in his authoritative and delightfully readable account, “Endless Forms Most Beautiful” (W.W. Norton, 350 pages, $25.95), the modern synthesis claimed that macroevolution – the emergence of new body plans – is microevolution writ large.

When the means for testing this exhilarating idea became available, it became clear that this is literally true: Most genes are concerned with embryological development – the making of an adult from its precursor (usually but not necessarily a fertilized or activated egg). Since then, there has been an explosion of research into developmental genetics. We now have an explanation of why, and also overwhelming evidence that, macroevolution is microevolution writ large.

Mr. Carroll’s book is an extended essay by someone who has participated notably in this work, setting forth and exploring its implications. He has named his book for the newest branch, which concerns embryonic development and its changing molecular mechanisms over geologic time (“Evo-Devo”), but it takes in many more ideas that just that.

Genes are made of DNA. DNA encodes proteins; proteins, in innumerable modifications, make cell chemistry and the parts of cell structure; and cells make up organisms. All this was known in the early 1960s. What was not clear was that biological form – the shapes of organisms and the number, disposition, and functions of their different body parts – was a consequence of information stored in the genes. It was not known how, at the molecular level, that information is used in developing embryos. Then came molecular biology: genetics and biochemistry coupled in a reductive search for mechanisms.

From this research there emerged the unexpected discovery that there are several different kinds of genes. Some genes that act during development are very, very ancient – presaged in animals living some 500 mil lion years ago. These “developmental” genes or their easily identifiable descendants still function in the development of modern organisms. Yet they do not directly make parts of cell structures; rather, they influence other, “younger” genes that do so. They cause certain genes to be expressed (or not) at a particular time in development and for a particular interval.

The consequences of such complex control cascades for the form achieved during the course of development are astonishing and fundamental to understanding the history of life on Earth. How and when certain genes turn others on or off differs from one animal body plan to the next; by virtue of differences of timing and location within the developing embryo, the whole range – the staggering complexity of animal shapes and functions – can be and is generated. These are the “endless forms most beautiful” – forms ranging from the spines and body armor of stickleback fish to the gorgeous eyespots of butterflies to the elegant limbs of deer and to our own overgrown, but sometimes useful brains – cited by Darwin 146 years ago in the final lines of On “The Origin of Species.”

That nature, acting in organic evolution, is a tinkerer is an old insight of comparative biology. Its full force can be felt only now, however, with the rapid maturation of evo-devo. There are many body plans displayed by extant (plants and) animals. But it turns out all the plans, extant and extinct, are variations on a small number of themes. In animals, perhaps of just one theme: the appearance of bilateral symmetry, segmentation, and serial differentiation of body segments.

The patterns created are determined by the chemical structure of both the regulatory and target genes, and this structure is in turn determined by the copying of genes from one generation. This copying is very accurate, but it is not perfect. Accidents – mutations and other changes in composition of the genome – happen at random. What happens thereafter, however, is the opposite of chance.

When an accident happens, the result may be a failure of development; that particular organism will then vanish from the population. Or the accident may have no significant effect on development; the resulting organism remains in the population as a cryptic variety. But it also may be favorable, and if so, it will be selected for. (This is not at all a new formulation in evolutionary biology, but thanks to evo-devo, it is now demonstrably true.) The history of form among the living things on Earth, macroevolution, is the relentless increase of information in the biological world.

It is ironic that this book emerges now in America, recounting for laymen the story of additions to the already vast literatures of embryology and organic evolution, at the same moment as the old obscurantist anti-evolution and anti-science has come, yet again, to the nation’s courts in the effort to disfigure science teaching in public schools. So many now believe in all sincerity, or are being led to believe, that discoveries such as these of evo-devo are somehow inimical to the mysteries of creation, or to living a good life! Not ironic: tragic.

Mr. Gross is university professor of the life sciences, emeritus,at the University of Virginia.