It's safe to assume that at some time or another, each of us has pondered what happens to us after our physical bodies perish. In fact, that metaphysical speculation may even predate our species. Scientists have found evidence that the Neanderthals, a now-extinct variety of primitive humans, performed burial rituals that suggest they may have believed in an afterlife.
As Homo sapiens took over the planet, our early ancestors developed a similar belief. Most ancient cultures had religions built around some version of immortality, in which the soul -- that is, our individual consciousness -- survived after the flesh perished, either as an individual spirit or part of some greater consciousness. Some believed that the spirits of dead ancestors remained in the places they'd lived, while others thought that they journeyed to a realm of the dead, or eventually were reborn, though not necessarily in human form. Others believed that after death, a person's essence merged back into a great spirit, just as his or her body was absorbed by the Earth. Gradually, as civilizations evolved, humans developed more elaborate beliefs, ranging from the Hindu samsara, which is the cycle of birth-death-rebirth from which souls ultimately can escape by becoming more spiritually advanced, to the Christian concept of heaven and hell.
Some have theorized that the desire to believe in an afterlife, and to create a vision of it, is encoded in our genes. But many people over the centuries, including famous figures, from philosopher Friedrich Nietzsche to music icon John Lennon, have rejected the idea of life after death. Science fiction novelist and biochemist Isaac Asimov even once said that he was glad there wasn't a heaven, because it sounded like a boring place to spend eternity.
The question of whether or not life continues after physical death, however, has been a very difficult one to answer, and it may always be. Some point to near-death experiences -- in which people who've recovered from cardiac arrest recount memories of leaving their bodies, encountering bright lights or tunnels and speaking with ethereal beings -- as an indication that an afterlife exists. Oncologist Jeffrey Long, author of the recent book "Evidence of the Afterlife: The Science of Near Death Experiences," has studied 1,600 such incidents across the globe, and says that despite extensive scientific research on NDEs, there's no conclusive explanation to refute the notion that they provide a glimpse of the next world.
The question of whether there's life after death is complicated in part because it depends upon another question: What exactly is life? Is consciousness a biological process, or is there a separate spirit or soul within the flesh-and-bone body that makes it alive? While it might seem that a soul would be a prerequisite for having an afterlife, there is an alternative possibility. Some researchers in artificial intelligence -- that is, the effort to create machines that can emulate or even surpass human thinking -- have speculated that what we think of as consciousness is actually the equivalent of a computer's operating system, a sort of biochemical software program. Someday engineers may even be able to duplicate the essence of a person and upload it to a computer, a mechanical body, or even to a flesh-and-blood body donor. The idea was first floated by computer scientist Vernor Vinge back in 1985, and more recently, inventor-futurist Ray Kurzweil and others have said that they expect such mind-duplication and transfer to be possible within 20 to 30 years. So the safest answer to the life-after-death question may simply be: If it doesn't exist now, it may well exist someday.