The following paragraph may link into our conversation, yesterday, after coming back from African Steel: we discussed creativity being fuzzy and all over the place (messy bits; binary logic in handwritten notes with Charles Boole; comparing that to automated learning systems); Charles Darwin's or Leonardo DaVinci's notebooks &c. Did you know that Bill Gates bought Leonardo Da Vinci's notebooks, in July 2015?
As far as the "psychological" influence of co-operation is concerned, it appertains to the internal resistances of the organism. The worker, when be is labouring alone, undertakes and carries out all actions on his own initiative and his own stimuli. He has to appropriately tune his nervous and muscular apparatus for each action quite independently; while in a joint effort this adaptation process goes on to a large degree due to imitation, i.e. in a much more mechanical and automatic way, thus decreasing considerably the inner resistances of the organism of the imitator. The stimulating influence of the apparent success of the efforts also helps to lower internal resistances, etc.