time_units: generations
demes:
- name: deme1
  start_time: .inf
  epochs:
  - {end_size: 1, end_time: 0, start_size: 1}
- name: deme2
  start_time: .inf
  epochs:
  - {end_size: 1, end_time: 4.0, start_size: 1}
pulses:
- {sources: [deme2], dest: deme1, proportions: [0.9], time: 4.0}
migrations: []