Cooperation is when people work together to achieve a common goal. Most often, cooperation leads to better results than any singular person could’ve achieved, though I believe that this has limits. When people cooperate, they combine their skills, working to cover any gaps in their knowledge with the other peoples knowledge. For example, you may have a group of people writing a comic book, and this team would normally include a writer, an artist, an editor, and normally many more. If any one of these people, perhaps the writer, tried to make a comic on his own, then the art would probably be horrid, or barely passable, while if the artist tried, the art would probably be wonderful, but the story sorely lacking. Combined, however, they manage to create a wonderful story to be enjoyed, as well as images to accompany it.
Though, it is important to note that gathering a large number of people just for them to share their skills won’t often work out well. This is because they’ll all want to do everything their way. Let’s take the the artist from the previous paragraph. With one artist, drawing up images based on what the writer wrote, you’ll get a consistent look and feel to the art. The writer, though, isn’t completely devoid from the writing process, as he’ll edit what the artist is drawing to make it more accurate to what he imagines the things he wrote. The artist as well is not completely left out of the writing process, and if he disagrees with the writer, and neither of them budge on what they think is right, then they’ll go their separate ways and the comic book won’t be made. More often, they’ll cooperate and fine-tune the writing or art to be the best they can make it. Now, imagine you have 50 or so artists and 50 writers, all of whom are trying to adjust the comic book to be the way they imagine it. It would be pandemonium, and at least a couple of these writers and artists will disagree with each other, and even if they sort it out, another is bound to have his own image of what it should be. Cooperation is therefore limited to a rather small number, to ensure the best result without pandering to the whims and wants of every singe average Joe off the street.
I believe three is a good number for a group, as specializations in a wide array of necessities can be well divided among them, such as writing, drawing, and whatever it is that editors do. Three also allows for quick decisions without mass voting on every topic, and even quick tie-breakers when there is a split vote.