What is a soul?

According to Dictionary.com:
Soul: the principle of life, feeling, thought, and action in humans

What is a soul? By definition, it is the very essence of what makes us human. It is our personality, our feelings, and thoughts, and ability to move about as humans do.

Having grown up as a Christian, and recently changing my views, some new thoughts have arose as to what a soul really is, and what it does. I suppose I began thinking of this to weigh out the likeliness of the existence of the soul.

For comparison, I tried thinking of something that may be animated that we can all agree does NOT have a soul. I thought of a robot.

Now, Question 1: What happens when you replace a human's "essence" with robot parts? They've already been transplanting mechanical hearts for some time, and I know it seems far fetched right now, but the following links lead me to believe that it may be possible one day to also replace an ill brain with a mechanical one. The links demonstrate robots that can learn, and basically think for themselves. They do things they are not programmed to do. If they can do this, why wouldn't they be able to put that same programming to run the basic motor and social functions of a human being, once our technology becomes advanced enough?

http://science.discovery.com/videos/brink-package-robots-become-human.html

http://uk.video.yahoo.com/watch/4103223

http://www.youtube.com/watch?v=xRR33WDFi_k

(there are many more great videos out there about the technological advances they've made with robots... you should google it)

Now, Question 2: What happens when a robot gains the essence of what makes us human? We've already seen a glimpse into robots being made with emotions, reactions, thoughts, etc. Does this then mean they have a soul? No, I would say not, and you probably agree. So what sets humans apart? If it's not our ability to think and react in our own ways, then is it simply our flesh that can harbor the soul? Why is it then taught that animals have no soul? I have had many pets in my lifetime, and I can't honestly say that they don't have their own personalities and thoughts and feelings.

And really, if you think about it, our human brain works much in the same way that the robot ones would, in that it passes signals from one main point to complete the motor functions. Take this clip from Wikipedia.com to understand how the brain processes thoughts:
"A neuron (also known as a neurone or nerve cell) is an excitable cell in the nervous system that processes and transmits information by electrochemical signalling. Neurons are the core components of the brain, the vertebrate spinal cord, the invertebrate ventral nerve cord, and the peripheral nerves. A number of specialized types of neurons exist: sensory neurons respond to touch, sound, light and numerous other stimuli affecting cells of the sensory organs that then send signals to the spinal cord and brain. Motor neurons receive signals from the brain and spinal cord and cause muscle contractions and affect glands. "

All of this leaves us with Question 3: If the soul can only be defined by what can also be possessed by what we know to souless, then can a soul truly exist? And if the soul can not, then in turn, can God?