Darwinian Defence theory ...
I was discussing the art of fencing with someone just this morning (the 'fencing' that utilizes nasty pointy steel things - as opposed to the wooden dog-retaining type) - and it became clear that great 'defence' was at the heart of the game of all the truly great fencers. If we think about it - it becomes clear as to why this is so ...
Simply and crudely put - centuries ago, when fencing was developed as an art form - only those fencers who had effective defence, survived long enough to teach anyone their method. Those without defence, were simply killed in combat - and wern't around long enough to teach anyone their (flawed) method.
This concept is at the heart of the Darwinian theory of evolution. Those traits that allow one species to survive and dominate, also allows that species to propogate and flourish - that is: to stick around long enough to pass on those succesful characteristics to their offspring - while those species that lacked the necessary survival characteristics, simply didn't survive long enough to reproduce and flourish - end of story!
These Darwinian forces are also what drives the development of the 'reality based' martial arts systems: BJJ, boxing, kickboxing, etc. The stuff that doesn't work gets left on the roadside along the way - while those techniques and strategies that do work, survive the test of time - and combat.
DEFENCE - that is, the ability to survive long enough to be able to train again next day (or next week) - is at the heart of long-term art/survival/development. When in doubt, work your 'defence' - become the most difficult animal to kill in the Jungle - and not just the 'most dangerous'.