d) Paleontologists still argue about the origins of major groups, though new fossil finds since Darwin's time have cleared up many of the disparities in the fossil record. Even during Darwin's lifetime, some transitional forms were found.
c) Today, many years later, many believe that evolution has progressed at the same steady rate and that the absence of transitional forms can be explained by Darwin's argument that there are huge gaps in the fossil record and that transition usually occurred in one restricted locality.
a) Others, however, believe that the fossil evidence suggests that, at various stages in the history of life, evolution progressed rapidly, in spurts, and that major changes occurred at these points.
b) An evolving group may have reached a stage at which it had an advantage over other groups and was able to exploit new niches in nature. Climate change may also have produced a "spurt", as might the extinction of other groups or species, leaving many niches vacant.
