I've written numerous articles that until the Industrial Revolution, mankind worked a 20 hour week. There was a holiday every second day. And when harvest came, there wsa a 3 hour break in the middle of the day. All of this is recorded in books from France and the UK.

More than that, mammals generally work a 20 hour week in which they search for food, secure their homes, etc. The rest of the time they sleep or stand around.

Our bodies did not evolve to work a 40 hour week.