I am Caucasian (well mostly, might be some Cherokee a couple three generations back) I have found NO credible evidence to suggest the Caucasians came out of Iran. Regardless of what the word Iran means. Evolution is a man created scientific methodology that institutionalizes man made models and systems that decide who is most fit. Simply put, evolution is the doctrine of the mini gods.
What in the Wide World of Sports does evolution have to do with migration? Amazing!
That is the historical geographical root for the Indo-European race - whether you care to believe it or not is up to you. (smile)
The theory is that the "Indo-Europeans" originated in the region of Northern Iran and moved outward. It's a geographical designation.
Also, the definitions of the various sub-groups of Indo-Europeans are linguistic and cultural as much as anything else.
As to evolution, there is the social form as well as the biologic sense of the word. I'm not sure about biology, but I am certain that the Europeans have evolved culturally-- for example we no longer hang the severed heads of former enemies over our doors as we did around 500 BC. I call that improvement