We were prisoners of nature. But the more we emancipated ourselves from nature the more we fell into dependence on the social relations we developed to dominate nature. As human society progressed a division of labour emerged. The more advanced the society, the more detailed the division of labour. Over the centuries a majority of people have lost control over the products of their labour, the tools they use to produce things and the very process of working itself.
Mental labour is separated from manual labour.
Both become subordinated to machines. We work on parts of things instead of seeing the whole. Under capitalism alienation is at its most complete. We sell our labour to an employer. For the duration of that contract they can do with us what they will.