Originally, deme Y had a population size of 2415, which changed to 9040 around 8520.7232 generations ago and has not changed since.
time_units: generations
demes:
  - name: Y
    start_time: .inf
    epochs:
      - start_size: 2415
        end_time: 8520.7232
      - start_size: 9040
        end_time: 0