See also my comment at https://news.ycombinator.com/item?id=35679767 showing the 1975 hypothesis could not be validated in a 1979 paper, and how even at the time it was "difficult to seriously entertain the notion" Hess proposed.
See also the thread at https://news.ycombinator.com/item?id=35667066 where one of belltaco's citations actually demonstrates that total vertical eye aperture - not pupil size - is the biggest predictor of mental state. Pupil size wasn't even considered, but the remaining variance is too small for pupil size to be a significant predictor. Total aperture is even easier to see than pupil size.
In other words, there's a bunch of citations, but no convincing support presented for the evolutionary hypothesis.
Rather like the "just so" stories of evo psych.
[0]: https://en.wikipedia.org/wiki/Just-so_story