How long has this flexible work option existed?
Job sharing is not a new concept. We're just making it more accessible.
Sharing a role / job share has been around in education, hospitals, and the public sector for ages. Also, many other industries have been doing it, without knowing it. For example, a copywriter and art director at an advertising agency can in many instances stand in for each other; and shift workers that require a handover every day are in many ways sharing a role too.