private void applySystem(System world, Actor actor) {
    //
    //  Assign skin texture based on prevailing climate-
    //  TODO:  Blend these a bit more, once you have the graphics in order.
    final Trait bloods[] = {
      DESERT_BLOOD,
      FOREST_BLOOD,
      TUNDRA_BLOOD,
      WASTES_BLOOD
    } ;
    Trait pickBlood = null ;
    ///I.say("Applying system: "+world.name+", climate: "+world.climate) ;
    for (int n = 4 ; n-- > 0 ;) {
      if (bloods[n] == world.climate) {
        final float roll = Rand.num() ;
        final int index ;
        if (roll < 0.65f) index = 0 ;
        else if (roll < 0.80f) index = 1 ;
        else if (roll < 0.95f) index = 3 ;
        else index = 2 ;
        pickBlood = bloods[(n + index) % 4] ;
      }
    }
    if (pickBlood != null) actor.traits.setLevel(pickBlood, 1) ;
    //
    //  Vary height/build based on gravity-
    //  TODO:  Have the citizen models actually reflect this.
    actor.traits.incLevel(TALL, Rand.num() * -1 * world.gravity) ;
    actor.traits.incLevel(STOUT, Rand.num() * 1 * world.gravity) ;
  }