Contrary to popular belief, Unicorns are not related to horses but instead are descended from the Siberian Unicorn.
- their fur became whiter
- they became slightly smaller
- they have an above-average sense of sight (compared to other rhinos)
- they started to develop a mane (optional)
Given these characteristics, how plausible is this and what evolutionary pressure would lead them down such a path?
NOTE: magic dose not exist in my story.