Ancient to Modern Languages Question?

I am an economist with a question on the development of languages. In economics is the concept of diminishing returns but also of technological improvements. Saying someone is pretty, very pretty, very very pretty, very(repeated 23 times) pretty has diminishing returns. At some point a person choses an optimum against their preferences. At the same time, people tend to innovate and develop entirely new words and ways of saying things. Have there been permanent structural changes in languages that reflect added efficiency and innovation? I have no linguistic training, but I am curious on the brain/culture/evolution interaction and realized we have a great resource measure in the changes between ancient tongues and modern tongues, though possibly mediated by the nature of more formal writing and no ancient remaining conversations. If so, could you recommend some readings on this?