It might depend on which tools you're using. When I'm doing historical research for how a function evolved, I normally run "gitk" on the file, and walk through

It might depend on which tools you're using. When I'm doing historical research for how a function evolved, I normally run "gitk" on the file, and walk through the commits; the full commit message is shown together with each diff to the file. It used to be even better in the past, when gitk showed the full commit diff, instead of the diff to just the file I passed on the command line, but "git show" on the commit hash (or another gitk which is not filtered to a path) is good enough.