Given they have similar hairstyles, and there's really not that much of a time separation in an evolutionary sense between Vulcans and Romulans, here's something I've wondered ...
Are Romulans capable of doing a mind meld? And do they have to experience Pon Farr every 7 years too?
From an evolutionary point of view, its likely that there just wasn't enough time for them to evolve past that (I mean, 2000 years is virtually nothing on an evolutionary scale)... but its also possible the Romulans are just Vulcans who spent a lot of time in a different region of the planet Vulcan in the past (prior to the separation) that has the right conditions in place which did not instigate Pon Farr (epigenetics at play).
Or they could have been something the Vulcans experimented with prior to the teachings of Surak... so genetic manipulation perhaps? Their version of Augments that didn't develop Pon Farr perhaps?
Alternatively, its possible that Romulus itself affected their biology via epigenetics so they wouldn't develop Pon Farr - 2000 years could certainly be enough time for this to happen, and epigenetic changes can happen in a single generation... plus within the context of Trek, it wouldn't be the first time a planet could affect humanoids very quickly and permanently.
Also, I wonder if the Vulcan Pon Farr might be connected to the Vulcan's self control (and not strictly part of biological evolution).
Since Romulans do not practice meditation or emotional control like Vulcans, its possible they never developed either telepathy or Pon Farr.
And the differences could be passed on via genetic expression perhaps.
Sure, the potential for Romulans to develop both is there, but otherwise, because they don't meditate, those never manifested.
We know that Vulcan brains are rather powerful, so maybe it has more to do with the effects of meditation and/or extreme emotional control and desire for logic and how it changes the biochemicals in the Vulcan body.
