@Summerkat:

My high school analogy is operating under the assumption that being human is a step in a forward progression. It is a higher birth than whatever our last life was, and is a lower birth than whatever the next one is. I acknowledge that I have no way of knowing for sure if this is true or not. You may be right, and we just wear this life as one skin; it may not be part of a hierarchy at all.

I think it is far more likely that we will have digital immortality before we are able to greatly extend our physical lifespans. Neural scanning is not that far off. Artificial neural networks are already being created in neuroscience labs using super computers and mathematical formulas; granted, they are much smaller versions of what our brains look like. Computer processing speed will exceed the human brain's capacity within the next 20 years, 30 tops.

I wouldn't worry about the size of the human population. Any discovery to grant immortality will surely be expensive and only a select few would be able to afford it, unless it comes in the form of a technological revolution. Once humans are able to literally plug in their brains, it won't be a stretch to copy ourselves.