Originally, deme U had a population size of 9400, which changed to 2578 around 3377.9105 generations ago and has not changed since.
time_units: generations
demes:
  - name: U
    start_time: .inf
    epochs:
      - start_size: 9400
        end_time: 3377.9105
      - start_size: 2578
        end_time: 0