They were once regarded as deceptions planted by evil spirits, but fossils eventually came to be recognized as Exhibits A, B and C of the history of life. Those stony specimens are the only direct evidence of what happened in the eons since the first rudimentary cells emerged on Earth some 3.6 billion years ago.
Unfortunately, the fossil record is incomplete, as Charles Darwin himself realized. He surely would have been delighted to see the riveting discoveries made by paleontologists in the subsequent century and a half. These new fossils eloquently reinforce his conviction that "endless forms most beautiful and most wonderful have been, and are being, evolved." The iconic winged Archaeopteryx, as well as newly described feathered fossils from China, show the transition from dinosaurs to their only living descendants, birds. Fossil whales with limbs demonstrate the evolutionary steps some mammals took to return to the sea.
Now there is new and powerful evidence in Tiktaalik for the steps that backboned animals took to crawl out of the sea in the first place. Many who reject evolution in favor of divine creation claim that the fossil record doesn't contain the so-called transitional species anticipated by Darwin's theory. This ancient, walking fish is yet more evidence that such an argument is simply wrong; all sorts of missing links preserved in exquisite detail have been and will be discovered.
Is the discovery of Tiktaalik a pivotal moment that profoundly shifts the balance in the tension between those who accept evolution and those who question it? Probably not. Those who regard creationism as dogma will probably remain unmoved by any manner of scientific evidence. For those who are uncertain, however, the fishapod may be a source of enlightenment, a demonstration that we can recover ancient clues to events clearly predicted by the theory of evolution.
That theory is the framework for all modern biology, from the study of fossils to the mapping of the genome, but it is also profoundly practical in application. Scientists are debating the likelihood and timing of a horrific pandemic caused by avian flu. Those who worry about that possibility and reject evolution live in a world of contradiction. If the H5N1 virus, the infective agent for avian flu, adopts a new lifestyle and moves directly from one human host to another, it would be because it evolved that capacity.
Indeed, evolutionary theory shapes both our health and our future. As Darwin noted, the survival of each species depends on how well it fits into changing environments. We know that ecosystems are changing on a global scale. As documented by the fossil record, some species in the past thrived under new conditions, while others, ill adapted to change, went extinct. Who will be the winners in the hot, deforested, carbon dioxide-- enveloped world of the future? It won't necessarily be us.
Novacek is a curator of paleontology and the provost of science at New York's American Museum of Natural History