Owen Barfield's work on the evolution of consciousness stemmed from his observation (e.g. in History in English Words, or Poetic Diction) that words began as 'poetic', broad, complex and containing of 'references to inner states; and had become narrower, simpler, more 'literal'.
His favourite example was 'spirit' which originally contained meanings similar to ghosts and non-material phenomena and also simultaneously meant 'wind'. One complex word meaning many things together is replaced by several separate words each of which are more specific.
Another trend in the changing meaning of words that I have noticed is for words to lose their force and strength.
'Anon' - as in 'I will do it anon' - for Shakespeare meant immediately, and for us means sometime or another (and perhaps never).
'Naughty' - for Shakespeare meant really wicked, while for us it means a bit mischievous.
'Fantastic' and 'Fabulous' used to mean beyond comprehension and beyond belief, but they now mean no more than a generic positive endorsement.
"Vile" used to meant utterly contemptible, but now is 'something I personally happen to dislike'.
Presumably, this phenomenon is an example of habituation or tolerance; when the same dose of any strong stimulus will, when repeated and repeated without catastrophic outcome, progressively lose its effect.