public function isDescendant($group = null) {
    if (is_numeric($group)) {
      $group = Group::factory((int) $group);
    }
    if (!isset($group->guid)) {
      return false;
    }
    // Check to see if the group is a descendant of the given group.
    if (!isset($this->parent)) {
      return false;
    }
    if ($this->parent->is($group)) {
      return true;
    }
    if ($this->parent->isDescendant($group)) {
      return true;
    }
    return false;
  }