Y deme's population was steady at 6106 before it changed to 3996 7985.7 generations ago, maintaining that number to the present.
time_units: generations
demes:
  - name: Y
    start_time: .inf
    epochs:
      - start_size: 6106
        end_time: 7985.7
      - start_size: 3996
        end_time: 0