Why Darwin Matters_ The Case Against Intelligent Design - Michael Shermer [9]
Where Are All the Fossils?
Evolution is a historical science, and historical data—fossils—are often the evidence most cited for and against it. In the creationist textbook, Of Pandas and People—one of the bones of contention in the 2005 Intelligent Design trial of Kitzmiller et al. v. Dover Area School District, in Dover, Pennsylvania—the authors state: “Design theories suggest that various forms of life began with their distinctive features already intact: fish with fins and scales, birds with feathers and wings, mammals with fur and mammary glands. . . . Might not gaps exist . . . not because large numbers of transitional forms mysteriously failed to fossilize, but because they never existed?”16
Darwin himself commented on this lack of transitional fossils, asking, “Why then is not every geological formation and every stratum full of such intermediate links?” In contemplating the answer, he turned to the data and noted that “geology assuredly does not reveal any such finely graduated organic chain; and this, perhaps, is the gravest objection which can be urged against my theory.”17 So where are all the fossils?
One answer to Darwin’s dilemma is the exceptionally low probability of any dead animal’s escaping the jaws and stomachs of predators, scavengers, and detritus feeders, reaching the stage of fossilization, and then somehow finding its way back to the surface through geological forces and unpredictable events to be discovered millions of years later by the handful of paleontologists looking for its traces. Given this reality, it is remarkable that we have as many fossils as we do.
There is another explanation for the missing fossils. Ernst Mayr outlines the most common way that a species gives rise to a new species: when a small group (the “founder” population) breaks away and becomes geographically—and thus reproductively—isolated from its ancestral group. As long as it remains small and detached, the founder group can experience fairly rapid genetic changes, especially relative to large populations, which tend to sustain their genetic homogeneity through diverse interbreeding. Mayr’s theory, called allopatric speciation, helps to explain why so few fossils would exist for these animals.
The evolutionary theorists Niles Eldredge and Stephen Jay Gould took Mayr’s observations about how new species emerge and applied them to the fossil record, finding that gaps in the fossil record are not missing evidence of gradual changes; they are extant evidence of punctuated changes. They called this theory punctuated equilibrium.18 Species are so static and enduring that they leave plenty of fossils in the strata while they are in their stable state (equilibrium). The change from one species to another, however, happens relatively quickly on a geological time scale, and in these smaller, geographically isolated population groups (punctuated). In fact, species change happens so rapidly that few “transitional” carcasses create fossils to record the change. Eldredge and Gould conclude that “breaks in the fossil record are real; they express the way in which evolution occurs, not the fragments of an imperfect record.”19 Of course, the small group will also be reproducing, following the geometric increases that are observed in all species, and will eventually form a relatively large population of individuals that retain their phenotype for a considerable time—and leave behind many well-preserved fossils. Millions of years later this process results in a fossil record that records mostly the equilibrium. The punctuation is in the blanks.
The Evidence of Evolution
In August 1996, NASA announced that it discovered life on Mars. The evidence was the Allan Hills 84001 rock, believed to have been ejected out of Mars by a meteor impact millions of years ago, which then fell into an orbit that brought it to Earth.20 On the panel of NASA experts was paleobiologist William Schopf, a specialist