Which would indicate that a series of fossils represent the evolution of the horse?

• A. All of the fossils were found in the same layers of rock as horse fossils.
• B. All of the fossils are completely identical to horse fossils.
• C. All of the fossils show similar structures to that of the modern horse.
• D. All of the fossils were located in the same place on Earth as horses.

Answer: (C)

A series of fossils that shows gradual changes in structure over time provides evidence of evolution in a lineage. If the fossils share basic structural features with the modern horse but display progressive differences, they indicate how ancestors evolved into the modern form, showing a line of descent rather than just random similarity. This pattern—progressive change within related fossils—is how scientists trace the evolution of horses. Being found in the same rock layer, or being identical to modern horses, or simply located in the same place on Earth doesn’t demonstrate that temporal sequence of changing forms, so they don’t provide the same clear evidence of evolutionary progression.