The start of the sentence, which you have excluded from your quotation reads 'All these techniques, though developed for the exploitation of wild cereals,' I think this is important context.
The techniques and tools were developed to harvest, store and process wild cereals. But, as there would be no point in planting crops if you did not already have the means to harvest, store and process them, those tools and techniques are prerequisites for arable farming, i.e. 'something that must exist or happen before something else can exist or happen'.
So Jared is saying that domestication of plants could not happen without early humans already having the understanding and the means to process the crops.
I don't think Jared means that humans domesticated plants unconsciously, but that having the skills they would need to maximise the benefits of doing so, was a step which brought them closer to that domestication, although it was not taken with that intent.
NB: If anyone is wondering where the ‘history’ is in this answer, it was made when the question first appeared in Literature SE and was migrated with it!