Oooof... how to explain this one...
You shouldn't say 'in explanation of', as it isn't the best way to construct the sentence.
To say 'to explain' in there is the best way to say it. In full, it means '...put forward in order to explain...' which is the meaning you want here.
To say 'as an explanation of' is also correct. Roughly, it can reworded to say the 'hypothesis' is treated 'as an explanation', or, in this sentence, 'put forward' as such.
To say 'in explanation of' has a different meaning. I cannot explain it easily (hoping someone can), but the construct would normally be used to describe a replacement:
...supposition put forward in place of / instead of observed facts.
It shouldn't be used with the meaning you are trying to apply to it, as the meaning becomes unclear.