7421: "What I do in my book Critical Mass is to work my way slowly towards human society, hoping that I am going to sort of bring people along with me if I start off as I do with bacteria and collective behavior in bacteria, I think a lot of people would find that a lot easier to accept than the idea straight away that we do –we have these sort of collective modes of behavior. And flocking is a nice intermediate case. You see it in fish, you do see it in bacteria actually, but you see it in fish and also in higher organisms and in birds, of course. It was a mystery, for a long time, to zoologists how, particularly with birds, how they showed this synchronized movement. There are all sorts of theories about it. Some thought that there must be a leader somewhere that everyone else was following. And I think that in the ‘20s or ‘30s there were even some discussions about some sort of telepathy that the birds had – which sounds crazy but you can understand it because it does seem almost telepathic when you see these swooping behaviors. How on earth do they do that? But it turns out that one can mimic that sort of behavior in computer programs where you have these little computer birds that are programmed just to respond to what their immediate neighbors are doing, just the few birds around them. They align themselves in the same way as all their neighbors and follow, more or less, what they are doing – making sure that they avoid collisions. And that doesn’t sound, in itself, that doesn’t obviously sound like a recipe for this mass flocking that you see. You can imagine you will get a little bit of coherent movements here and there. But it turns out that with just those ingredients you can get this overall sort of flocking behavior. There’s software freely available on the web where you can see some of this happening, and it’s so fantastic to play with because it seems so familiar really, so lifelike, as you sort of twiddle the buttons to adjust the range that the birds respond. You get all sorts of complex behaviors, not just this standard flocking but this interweaving and so on – which we’ve all seen in the sky. And that’s really the striking thing. That these local rules, where they are just responding to their environment, are enough to cause this global collective behavior. And that’s much more...that’s a sort of plausible model because it doesn’t require the birds to be doing anything extraordinary if they are just taking into account what is going on immediately around them. And there is an analogy with physics because, for example, in magnetic systems, so in magnets which have got a lot of magnetic atoms in them that are stuck together in a crystal...generally speaking, each magnetic atom only responds to the magnetic fields of its near neighbors – but, again, that’s enough to give a global mode of magnetism where every atom is kind of pointing its magnetic needle in the same direction. That is what basically creates a magnet. So we know from physics that these local rules can give rise to global motive behavior, and it’s very nice to have now very clear examples from the living world."

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