Final answer:
A hypothesis regarding ancestor-descendant relationships that includes a time scale is called a phylogenetic tree, which illustrates the evolutionary relationships and timing of divergence from a common ancestor.
Step-by-step explanation:
An hypothesis regarding ancestor-descendant relationships that includes a time scale is referred to as a phylogenetic tree. A phylogenetic tree is a diagram that shows the evolutionary relationships among various biological species based on similarities and differences in genetic or physical traits. These diagrams can reflect evolutionary connections and can include a temporal aspect when they also depict how long ago species diverged from their common ancestor, often referred to as the tree's branches. With methods such as the molecular clock, which compares sequences of conserved proteins to determine mutation rates, scientists can estimate the timing of evolutionary events, even for those that occurred before complex life forms left a rich fossil record.