Two groundbreaking discoveries published last week, one in the field of paleontology and the other in biology, seem to rebut key creationist criticisms of evolution.

The first involved fossilized remains of Tiktaalik, a long, rather ugly fish that lived 375 million years ago. It's thought to be a so-called missing link between animals that lived exclusively in water and those that lived exclusively on land. It had an articulated neck that allowed it to turn its head side-to-side, something no fish can do but is necessary for survival on land. In the animal's pectoral fin were smaller versions of all three arm bones found in land-dwelling animals, as well as a proto-wrist and a handlike structure.

Over the years, evolution critics have frequently challenged scientists to come up with a "missing link" showing the transformation of one species into another. Since the discovery of Archeopteryx (the so-called feathered dinosaur found in 1861), we've known that birds and reptiles are close relatives. More recent discoveries continue to fill in the picture. There are a number of transitional fossils, including some showing the change from amphibians to the first reptiles and from reptiles to the first mammals.

One thing that helps make such finds persuasive to scientists is that they were predicted by evolutionary theory long before they were actually discovered. In the case of Tiktaalik, paleontologists knew exactly where to go looking. They predicted it would be found at the mouth of what was a tropical river 375 million years ago. They found it on Ellesmere Island, in the Canadian Arctic, where it had been deposited by tectonic forces.

The second discovery strikes directly at the heart of "intelligent design" — the concept of irreducible complexity. Creationists have long argued that a series of small changes cannot create new biologic machinery, because that would imply that a "useless" adaptation was preserved over a long period of time until its new role emerged.

But a group of researchers from the University of Oregon showed for the first time how this process can occur. They looked at a pair of hormones and the receptors into which they bind like a key in a lock.

They studied cortisol, a stress hormone, and aldosterone, which controls kidney function. Both developed from a common gene 450 million years ago. The scientists created that ancestral receptor in a laboratory. To their surprise, they found it could bind with either of the two hormones. That means a receptor for aldosterone existed long before the kidney hormone first appeared. It also means that the "irreducible complexity" of our endocrine system is reducible after all.

Given the age at which life emerged on Earth and the specific conditions that allow fossils to form, there will probably always be some gaps in the fossil record. Like any human activity, science reveals an imperfect picture of the world in which we live. But unlike religion, science is always subject to revision.

None of that makes science better than religion, just different. Educators and legislators needn't abandon their religious beliefs, only refrain from forcing them into science classes where they don't belong.