Final answer:
A fossil record with many different forms of the same organism over a long period of time suggests gradual speciation, characterized by the slow evolution of species with many intermediate forms.
Step-by-step explanation:
The rate of evolution that best describes a fossil record showing many different forms of the same organism over a long period of time is gradual speciation. In the fossil record, gradual speciation is indicated by many intermediate forms, showing a slow and steady transformation of species. This is contrasted with punctuated equilibrium, where the fossil record would demonstrate long periods of little change (stasis) interrupted by short, significant shifts in form and diversity, leading to rapid speciation. The presence of many intermediate forms over a long period suggests a gradual accumulation of small changes, rather than rapid bursts of change characteristic of punctuated equilibrium. For example, the detailed fossil records of human and horse evolution provide evidence for the process of macroevolution, demonstrating transitions over millions of years.