time_units: generations
demes:
- name: a
  epochs:
  - {start_size: 1}
- name: b
  epochs:
  - {start_size: 1}
- name: c
  ancestors: [b]
  start_time: 100
  epochs:
  - {start_size: 1}
migrations:
- rate: 0.01
  demes: [a, b, c]