What The Fossils

If at this point you're feeling overwhelmed with fossils, be consoled that I've omitted hundreds of others that also show evolution. There is the transition between reptiles and mammals, so amply documented

Sphecomyrma freyi petiole structure three-part mesosoma

> ancestral traits dérivée petiole structure three-part mesosoma

figure 13. Transitional insect: an early ant showing primitive features of wasps (open triangles), its predicted ancestor, and derived features of ants (filled triangles). A single specimen of this species, Sphecomyrma freyi, was found preserved in amber dating from 92 million years ago.

with intermediate "mammal-like reptiles" that they are the subjects of many books. Then there are the horses, a branching evolutionary bush leading from a small, five-toed ancestor to the proud hoofed species of today. And of course there is the human fossil record, described in chapter 8—surely the best example of an evolutionary prediction

At the risk of overkill, I'll briefly mention a few more important transitional forms. The first is an insect. From anatomical similarities, entomologists had long supposed that ants evolved from nonsocial wasps. In 1967, E. O. Wilson and his colleagues found a "transitional" ant, preserved in amber, bearing almost exactly the combination of ant-like and wasp-like features that entomologists had predicted (figure 13).

Similarly, snakes have long been supposed to have evolved from lizard-like reptiles that lost their legs, since reptiles with legs appear in the fossil record well before snakes. In 2006, paleontologists digging in Patagonia found a fossil of the earliest known snake, ninety million years old. Just as predicted, it had a small pelvic girdle and reduced hind legs. And perhaps the most thrilling find of all is a 530-million-year-old fossil from China called Haikouella lanceolata, resembling a small eel with a frilly dorsal fin. But it also had a head, brain, heart, and cartilaginous bar along the back—the notochord. This marks it as perhaps the earliest chordate, the group that gave rise to all vertebrates, including ourselves.

fulfilled.

In this complex, i-inch-long creature may lie the roots of our own evolution.

The fossil record teaches us three things. First, it speaks loudly and eloquently of evolution. The record in the rocks confirms several predictions of evolutionary theory: gradual change within lineages, splitting of lineages, and the existence of transitional forms between very different kinds of organisms. There is no getting around this evidence, no waving it away. Evolution happened, and in many cases we see how.

Second, when we find transitional forms, they occur in the fossil record precisely where they should. The earliest birds appear after dinosaurs but before modern birds. We see ancestral whales spanning the gap between their own landlubber ancestors and fully modern whales. If evolution were not true, fossils would not occur in an order that makes evolutionary sense. Asked what observation could conceivably disprove evolution, the curmudgeonly biologist J. B. S. Haldane reportedly growled, "Fossil rabbits in the Precambrian!" (That's the geological period that ended 542 million years ago.) Needless to say, no Precambrian rabbits, or any other anachronistic fossils, have ever been found.

Finally, evolutionary change, even of a major sort, nearly always involves remodeling the old into the new. The legs of land animals are variations on the stout limbs of ancestral fish. The tiny middle ear bones of mammals are remodeled jawbones of their reptilian ancestors. The wings of birds were fashioned from the legs of dinosaurs. And whales are stretched-out land animals whose forelimbs have become paddles and whose nostrils have moved atop their head.

There is no reason why a celestial designer, fashioning organisms from scratch like an architect designs buildings, should make new species by remodeling the features of existing ones. Each species could be constructed from the ground up. But natural selection can act only by changing what already exists. It can't produce new traits out of thin air. Darwinism predicts, then, that new species will be modified versions of older ones. The fossil record amply confirms this prediction.

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