They also evolve to remain socially relevant. Much of what has driven the move to add grappling to many arts that have little or no grappling is the popularity of MMA.
Much of what keeps TKD popular in spite of the art not embracing grappling are the character building and after school activity aspects that are seen in many schools; while sport TKD is often looked down upon by those in other martial arts and by some MMA fans, and while it is certainly not socially relevant in the US, the character building and after school activity elements are socially relevant, and so parents with kids seek it out.
In Korea, of course, Taekwondo has a great deal of social relevance: it is the nations national sport, and many aspects of taekwondo contain Korean cultural elements that are unimportant in western culture.
Much of the appeal of many Koryu arts is, in my opinion, similar to the appeal that archery and black powder weapons in the US (we have a hunting season for both); both are part of western cultural heritage. We fought our revolution with black powder weapons, and we all love Robin Hood. Groups such as the SCA touch on western cultural heritage in the same way.
As for modern arts, meaningful evolution of them is mainly with regards to unarmed defense against weapons that may not have existed or were uncommon at the time of the art's genesis, or which were simply not included at the time of the art's creation for one reason or another. Unarmed vs. unarmed art evolution seems to be more in the vein of the blending of different arts, much of which, as I said above, is driven by popularity and sport.
Daniel
Theres quite a few Takedowns, Grappling, Jointlocks, Throws, Clinches, and Submissions, overall serving Grappling and Ground Fighting in Taekwon-Do; Especially Close Distance Takedowns.
Im pretty sure Tae Kwon Do has them, as well.
However, if you meant in terms of Competitions, and Sparring, and going all MMA and insisting on Wrestling at some point or another during the match, then yes.
Tis all aspects. One might, for example, say that teaching Grappling on its own would be inferior to teaching Grappling with Striking. Let alone Ground Work and Blocking.
Now, just to clarify, i am not disagreeing with you. In fact, i agree. I am rather expanding on what you are saying, so as to ensure full retrospect of the Topic.
For example, since there is less regulation in how an engagement would take place today, people tend to essentially slam into each other. If theyre still standing after a few seconds, itll likely become a close distance match, based on either grappling, or a weird kind of Dirty Boxing, only without the Rules.
Moving on.
Even in Sport TKD, im seeing more and more Clinch-Ups. And although theyre swiftly broken up, it makes it clear that with regulations to allow what would essentially be Infighting, the Sport could evolve. On the other hand, the Sport is fine the way it is, in terms of Sport.
Another way of putting it, is the Two different views of Hapkido. One which has Contact Sparring, and the other which is focused on Self Defence Drills with resisting opponents; Some of which allow you to add in your own slight flavor. Which is highly comparable to Ju Jutsu.
The other way of looking at it, is that both Hapkido and Ju Jutsu operate on very similar concepts. And both work swell. And their emphasis is Close Distance Grappling (Maybe Grappling isnt the right word, but im drawing a blank for a better one).
They also teach Striking, however. And Blocking.
To make the same comparison, most forms of Karate, Kajukenbo, Kickboxing, TKD, and othersuch; Teach Grappling. But it is not the Emphasis; The Emphasis being Striking and Stand Up, which naturally includes Takedowns.
My summation being;
MMA as a Fighting Form is different to Cross Training. But its a matter of what you want to learn, and how you want to learn it.
Karate and Kung Fu used to be pretty much what came to mind when you mentioned Martial Arts.
Before that, Boxing.
Now, its a collective of numerous Martial Arts, rather than just one. Which can be depicted, by MMA.
Having said all that, and tiring my fingers out; I think more styles should teach No-Holds-Barred Contact Sparring, just for the experience.
It certainly wouldnt Harm Tradition.