Final answer:
Charles Darwin referred to the gradual change from an ancestral type as 'descent with modification,' influenced by the gradual geological theories of his time and contrasting with the punctuated equilibrium model suggested by the fossil record.
Step-by-step explanation:
The term Charles Darwin used to describe the gradual change from an ancestral type is descent with modification. This concept is a cornerstone of Darwin's theory of evolution, suggesting that species change over time due to the accumulation of inherited differences. This idea was influenced by the geological theories of James Hutton and Charles Lyell, who proposed that geological change occurs gradually over long periods of time, rather than through sudden, catastrophic events. Darwin's observations led him to conclude that a similar gradual process could account for the evolution of species. This process, known as gradualism, implies that significant biological change is the result of slow and continuous processes over time. On the other hand, the fossil record suggests a different model called punctuated equilibrium, where long periods of little change are interrupted by significant bursts of rapid change.