I don’t know what research they saw, but the claim was mainstreamed by the popular book “Sapiens”. The author romanticized past life and made claims that life was leisurely until agriculture came along and made us all miserable as we toiled working the soil. Before that we supposedly relaxed all day as our food was easy to catch and we didn’t have to build anything because we were always on the move. There are some very obvious problems with that statement that will be easily spotted by anyone who has ever done any hunting or camping.