[Atrocities]

What if the Klingons stole or were sold a bio-genetic weapon or material that when applied to a living being, say a Klingon operative, would by its design, mutate the operatives genes to make him look human. Now say that the person, who sold this biogenetic material, or the Klingons by accident, had altered it so that it became a cotangent. IE it would spread throughout the population base of the species that used it, mutating so that it only affected that species.

Lets just say for the sake of argument the Klingons bought this bio-genetic tool, altered it slightly for use with its covert operations, and whole by mistake, created a plague that altered the genetic structure of their race in such a way that they all became human looking.

An accident that epic could be used to explain why the Klingons in Enterprise era look like the Klingons in TNG while the Klingons in theTOS era look human. One could say that they acquired the biogenetic material during the Enterprise era and an accident occured thus mutating them all to look like humans, however by the time the events of TMP occured the Klingons were able to reverse the effects of the mutagen and regain their original apperance.

This would also explain why the Klingons of DS9 era consider the subject of the Klingons of TOS era to be something they do not discuss.

Just a thought.