Do fruit flies have free will?

If you find it hard to imagine how any such thing could be packed into a brain (hardly more than a tangle of neurons) that small, you are not alone. Scientists have basically viewed insects "as complex robots which only respond to external stimuli," says Björn Brembs of the Free University Berlin. Of course, lots of scientists think this about humans, too, viewing our brains as input-output devices responding to external stimuli, neurochemicals and earlier brain activity in a deterministic way that leaves no room for free will.