The segment evolution report shows you how your saved segments have changed over time, i.e. how the number of contacts has grown or decreased.
To access the segment evolution report for any of your saved segments:
Select Customer > Segment explorer > select a saved segment from the dropdown > Segment evolution
Or, go to Customer > Saved segments > choose a segment from the list and select the View dropdown > Evolution:
Choose to view the evolution of your segments by:
Next, you can set your date ranges for reporting at the top of this screen.
Select any of the pre-configured date ranges from the drop-down, or choose Custom Range to bring up the calendar tool and set your own range: