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If you enjoy reading books about evolution, the following books reviews also appear on The Science Shelf:
In Sudden Origins, University of Pittsburgh Anthropology Professor Jeffrey Schwartz has produced a book that will challenge -- even overwhelm -- its readers with a wealth of detail. Yet if they can stay the course, they will be rewarded with a thought-provoking new view of the history of life on Earth.
"Evolution is not a theory," argues Schwartz. "It is a phenomenon. What evolutionists ... strive to understand are the processes that make evolution tick. This is not an easy task, because evolutionary events occur over greater periods of time than any scientist, or generations of scientists, could observe."
Without taking on so-called "creation science" directly, Schwartz demonstrates that evolutionary theory is itself evolving, as all good scientific theories do in the face of new knowledge. What creation scientists cite as the theory's weaknesses, Schwartz presents as its strengths.
With a thorough detailing of the history of this century-and-a-half-long quest, even including notations in Darwin's original notebooks, he traces the development of our current understanding. That understanding emerges not as Darwinian doctrine, but rather as the result of a rich scientific conversation among colleagues and adversaries, all of whom share a common goal if not a common point of view: understanding the origin and development of, and relationships among, the diverse creatures that have lived on our planet.
A recurring theme in that conversation is one that creation scientists often seize upon. If life evolves gradually, where are all the "missing links"? Although that term conjures images of "ape-men," the challenge to the theory is much more serious than that. The fossil record is riddled with gaps.
Life forms evolve, it seems, in a kind of punctuated equilibrium. Successful species change slowly and gradually over millions of years, then new species originate suddenly, arising in dramatically different forms with, in many cases, no intermediate examples.
Scientists have proposed many explanations for the absence of transitional creatures, none of which have been totally plausible. They have tended to divide into two camps on that issue. One group has insisted that the intermediate examples will be found; the other has argued that geographic separation and environmental change drives rapid speciation.
Schwartz sides with the latter group and tackles two important unanswered questions in his "New Evolution" as to the underlying cause of novel characteristics that lead quickly to new species: (1) "How will novelty look when it does appear?" and (2) "How does more than one individual come to have a novel structure?"
The answer, he writes, lies in a class of genes called homeobox, whose importance was not fully appreciated until recently. These genes regulate the development of creatures from embryo through adult. Mutations in these genes propagate invisibly through the species as recessive and unexpressed, says Schwartz, until they are common enough that some individuals inherit them from both parents. That leads to fully developed novel features. Within a few generations, a new species emerges.
To Schwartz, this is the origin of species: "(T)he same kinds of structural building blocks are found among a wildly diverse array of organisms -- from yeasts to humans -- that have fashioned the resultant structures differently," thanks mainly to the differences between their developmental sequence. As a result, "seemingly distantly related and very dissimilar groups we call invertebrates and vertebrates are, in their genes, much closer than scientists even ten years ago could have imagined." One developmental sequence leads to animals with skeletons inside their musculature; another leads to the opposite arrangement.
"Given the potential of homeobox genes to be fully rather than partially expressed," Schwartz concludes, "we can appreciate why 'missing links' are so elusive in the fossil record. They probably did not exist."