Much has been written about our ability (or rather inability) to truly multitask. Arguments range from the increased overhead in task switching to our inability to focus fully on one more than one task at a time. Here is a new to the mix - bandwidth crunches in our mental router.
Apparently, the underlying phenomenon is well known. When we need to decide a couple of tasks in quick succession, there is a measurable delay if the second task starts too close to the first. In other words, tasks get processed in our brain, one after the other. This is called Psychological Refractory Period. Researchers have recently discovered that there is a part of our brain, that acts like a router, and when there is too much traffic, there can be a delay while the outstanding requests are cleared out. In other words, questions go to one location, setup as the first level helpdesk number. These are then processed and handed over to more specialized parts of the brain that can then complete the requested activity. Guess the old adage was correct:
One thing at a time,
And that done well,
Is a very good thing,
As many can tell
From an evolutionary point of view, this is such a sweet example of functional specialization in the brain. A simple architecture, but that is as scalable as possible. Rather than have each part of the brain understand everything, everything is done in specialized pockets, including the generalized functions that specialize in nothing more than pushing paper. Examples of this specialization abound, including this one that identifies the brain center that tracks time.
Back to the original point. Not only is multi-tasking unsustainable from a macro point of view, the brain processing itself is set up to be incompatible with doing more than one things at the same time. If you are talking and driving at the same time, the fact that your driving decisions are queued up awaiting the finalization of your retort to the angry spouse is not only scary, but a sure shot recipe for disaster.