Originally, deme Y had a population size of 9781, which changed to 2995 around 8879.819 generations ago and has not changed since.
time_units: generations
demes:
  - name: Y
    start_time: .inf
    epochs:
      - start_size: 9781
        end_time: 8879.819
      - start_size: 2995
        end_time: 0