How/Why did the brain form in the early life forms?

[WaveJumper]

The first brains came about in the precambrian or at the border with the cambrian around 560 million years ago when the first multi-celluar organisms emerged. It has always struck me how/why organisms developed brains. The brain must have emerged together with eyesight, since eyesight would be worthless without a brain. I can see how certain multicellular organisms might have evolved certain photo-sensitive cells into eye-sight, but how did they know, and what gave them information(the blueprint) how and why to construct a brain to make use of the eyesight? Did the brain form before the eyesight and the other senses? If so, what purpose would it serve? If it came about at the same time with the other 6 senses, what made it possible? How does the evolution theory address this question?

 

[Moonbear]

You can actually look at more simple/primitive organisms to get a handle on your question. Development of nervous systems would have preceded vision. If, for example, you look at worms, like the earthworm, they have just ganglia (clumps of cell bodies of neurons). Work your way up to insects, and some very simple brains start forming. The brains of insects have so few neurons that I think every individual neuron has been mapped. Keep working up from there, and you get organisms like lampreys that have basically the equivalent of nothing more than our brainstem. Moving into birds, huge brainstem, and a little bit of cortex stuck on the front (lots of visual processing going on there). Get to mammals, and the cortex starts to get proportionally larger relative to the brainstem, smoother in "lower" mammals, and more folded as it develops more in "higher" mammals.