All animals have their own unique type of Martial Art. For this reason, 'martial arts', in this sense are closely linked with the core of one's life and self-development - with emphasis on the nuance of self-defense. No sane animal ventures out into the world picking fights out of boredom. These violent bouts are costly and risky. Humans on the other hand can corrupt this process and turn violence into it's own form of entertainment.
Martial Arts are not about fighting, they are about surviving and surviving requires a means to protect one's self and adapt to situations. One such situation where a life-form often times faces death (and thus touches the deepest depths of it's life) is when fighting for its life. There are many creatures out there trying to eat each other and it becomes a matter of understanding the other's mechanism of attack so that one can strategise a defense and counter-attack. All creatures are locked within this cycle and this is why Nature's Will is beautifully, brutally balanced.
Through this process one can grow and learn more, actualising, and expressing in combat the unique forms manifested by their features. For example, there is a whole martial art style inspired by how a Praying Mantis moves and hunts its prey. This in itself is a recognition of the value of what Nature can teach through observation and application and a celebration of its Beauty.
For a human being the self-development (or Spirituality) aspect is more evident as opposed to fending off opponents trying to dissolve one to their stomach's cause. For a human being, martial arts can test one's limits, show our strengths and display our limitations. This is how we grow: From knowing where we are, where we need to go and understanding what needs to be done to get there. The process requires hard work but the heights reached have views worth climbing for!