Some of the changes between "ridged" Klingons however, could be due to two remaining factors 1). Klingons being cross related with subject peoples (as is common in human history's empires), and 2). Klingon physical body modification (hair depilation, skull binding, etc).
- 1). (1966-1969) Star Trek: The Original Series
- 2). (1979) Star Trek I
- 3). (1984-1991) Star Trek III, IV, V and VI
- 4). (1987-2005) Star Trek: The Next Generation, Star Trek Deep: Space Nine, Star Trek: Voyager and Star Trek Enterprise
- 5). (2011) Star Trek Into Darkness
- 6). (2017-Present) Star Trek: Discovery
There is little difference between 3 and 4 (head appliances seem smoother in the films). There are strong links between 5 and 6 (such as holes distal to the nostrils, on the cheek), but the 6th type of Klingons sometimes have very elongated skulls.
The hair accounts for a lot of the differences between Klingons, as in Star Trek I: The Motion Picture, they were given a Samurai's bald hairstyle, and in later Star Treks, they were given almost Elizabethan hairstyles inspired by Shakespeare, followed by long flowing hair similar to many ancient cultures. It is possible that the more pronounced features of Klingons 5 and 6 represent a more relict population with aboriginal features, where the most frequently seen Klingons of TNG, DS9, VOY and ENT were more cosmopolitan in their heritage. Finally, several ancient peoples of Earth performed head binding to shape skulls into a more conical shape, sometimes to differentiate social rank; the Huns, ancient South American cultures, etc. So it is possible that the Klingons seen in DSC practice this, or that it is a social trend at this time.