According to the 1911 Census of England & Wales, the three largest occupational groups then were domestic service, agriculture, and coal mining. By 2008, the three largest groups were sales personnel, middle managers, and teachers.
What we can first notice is one hundred years ago much of the work done in the economy was direct human labour. And much of that labour was associated directly with harnessing energy in the form of food or fossil fuels.
Today, the largest groups have little to do with production, but are more focused upon the management of complexity directly, or indirectly through providing the knowledge base required of people living in a world of more specialised and diverse occupational roles.
What evolved in the intervening hundred years was that human effort in direct energy production was replaced by fossil fuels. The contribution of fossil fuels to the economy can be expressed as being energetically equivalent to a huge slave supplement to our economy. The energy content of a barrel of oil is equivalent to twelve years of adult labour at forty hours a week. Even at $100 /bl, oil is remarkably cheap compared with human labour. As fossil fuel use increased, human labour in agriculture and energy extraction fell, as did the real price of food and fuel. These price falls freed up discretionary income, making people richer.