Many people in the post-industrialized era have problems with crowded teeth because there's not enough room in their lower jaws. The teeth sometime erupt crookedly and cause malocclusions, or misalignments of the teeth between the upper and lower jaws, which can cause chewing problems.

How did life begin? For those who reject the testimony of Genesis, the search is restricted to clues in nature.

One such clue is the minimum essentials required for growth and reproduction. If that number is small enough, then life might conceivably have formed by chance.

To the untrained eye, certain butterflies can look essentially identical to corresponding varieties of another species. This way they can evade predators, who won't eat them because the insects they're copying taste terrible.

Animal and plant cell DNA is so complicated that all the cellular machines that process, regulate, and manipulate it are constantly in need of cellular fuel. In fact, each animal and plant cell uses so much fuel that specialized fuel-production facilities called mitochondria are required.