'instead of acting as though people have a real will to do things, we assume everything is purely biological and thus must be "fixed" with drugs rather than by making different choices.' - how to teach people to make better choices is a difficult question, and i do think that the brain can change it's own chemistry without neccesarily needing drugs - however i also think drugs can be helpful for getting the brain into a state where the changes are easier to make - that doesn't mean i don't think drugs aren't over-proscribed by some doctors/psychiatrists - but then if they DO work clearly these people are going to advise that people use them - any other methods of retraining the brain (and i'm thinking about forming life-habits which leave you feeling good about yourself and not depressed) are more difficult in my humble expierence.
Do animals have will? i mean compared to trees, i know certain pets who can follow commands, who will go fetch a ball when you throw it. Aretehy just following their instincts or are thethinking about playing with their owners?
"That does not make any sense at all." - we have brains. I mean really Trees do not have brains, they respond in a different way, we wouldn't say they have a will when talking about how they react to things (though the chemical reactions they exhibit do serve mostly to protect them when that is possible) In the same sense our brains on a basic level function to keep our hearts beating - automatic functions which we don't control - we have many different functions, and if you want to call all of them will then go right ahead.
The point i was tying to make about complexity is that you can't just look at the rudimentrary parts - the whole is greater than the sum of the parts.
The whole of a human brain (when properly developed) has an emergent behaviour - which you can't describe just in terms of the molecules - please find out what emergent means and read some examples of it - it is really cool anyway - A dog's brain and will creates a different emergent property which we might call by a different name if it didn't tick all the box which we have decided human 'will' amounts to - it would still be categorised as a type of consciouness.
@Broken joystick - If you looked at the video you will see it is a medical exmpale of a person who has two sides of their brain (the cockpit in the scheme you propose) one side can draw, the other can talk, both can see things (because we have two eyes - one wired to each side of the brain) in the experiment it was clear that the side which could talk knew different things to the side which could write. (they were dissconnected surgically to prevent epileptic fits)
It is like the cockpit is split in two, and each side can get input from the outside world, but can only do a limited number of things - however your pilot seems to be split in two, as if one is driving each cockpit - is there two souls at work? Or is it one soul somehow inhabiting both sides of the brain but not able to communicate information between either sides (because of the surgery) except when he draws something with one half and then the other half looks at it and can talk about it...
That doesn't make much sense unless the pilot is split in two aswell. (again caused by a fairly simple surgical procedure)
"Is there some sort of threshold of complexity at which somethings goes from not having a will to having one?"
We have only really studied complexity since some time in the 60s (se: http://complexity.orconhosting.net.nz/) We don't current measure some threshold of complexity - but if i describe 'will' as an emergent phenomina then it is just that, a property of certain system - it only occurs when the system exhibits it - complex systems are really hard to breakdown into their composite parts and then say logically - 'oh this bit makes that happen, which leads to thing B, which means that the bit over the looks like it had free will'
So we can't go - anything with over 20 billion billion atoms, and 30 million connections between each atom has free will - we have instead to go 'this whole thing exhibits this behaviour' - now you can do really good science by comparing similar systems and there is cool stuf relating to complex foams and the stock market and how humans behave en-mass, along with neural networks - but this is still a very new area for science to be going into and explaining...