If evolution happens gradually as genetic changes are passed from one generation to the next, you’d expect the fossil record to show the transitional forms along the way. But it doesn’t always do that.
In some cases, the fossil record clearly shows a pattern of gradual change from ancestor to descendent. But more often, it seems to show jumps from one species to another with no transitional forms in between.
“It's quite rare to actually have examples in the fossil record where something has changed gradually in one particular direction over a long period of time,“ says Melanie Hopkins, curator and chair of the Division of Paleontology at the American Museum of Natural History.
