Do anyone of you have a clue as to why do we have all these sensory and motor decussations? Is there any evolutionary importance to these? Please do help!

Interesting question (I was not familiar with the word decussation before).

 

It seems to be related to the evolution from invertebrates (where the main nerves around the digestive tract at the front of the body) to vertebrates (where the spinal cord runs down the back). The arrangement of most of the internal organs is reversed as well.

 

More discussion here: https://neuroscience.stanford.edu/news/ask-neuroscientist-why-does-nervous-system-decussate

It seems, its still a mystery as to why they were reversed? By the way thanks for your help! I really appreciate it.