There is that part of the mind that assumes we are immortal, no matter how rational or informed we might be about the real state of the world and our own personal future - absent intervention - of aging, suffering, and death. Organized religion may have its origin in this, coupled with our tendencies towards anthropomorphism and desire for immediate answers to replace unknowns, even if those answers are incorrect. The line of thinking in a prehistoric society runs as follows: if we are immortal, then so are our dead ancestors, and who is moving the sun? These things lead to their natural conclusions.
To what degree is the inner assumption of immortality - in and of itself - something that drives public disinterest in work on rejuvenation biotechnology? I'm not completely convinced that it is important versus, say, the influence of modern religious culture, or the widespread mistaken belief that extending life would mean extending the period of frailty and suffering in old age. But it is a part of the puzzle: why are people so unwilling to help their future selves avoid pain, suffering, and death?
Most studies on immortality or "eternalist" beliefs have focused on people's views of the afterlife. Studies have found that both children and adults believe that bodily needs, such as hunger and thirst, end when people die, but mental capacities, such as thinking or feeling sad, continue in some form. But these afterlife studies leave one critical question unanswered: where do these beliefs come from? Researchers have long suspected that people develop ideas about the afterlife through cultural exposure, like television or movies, or through religious instruction. But perhaps [these] ideas of immortality actually emerge from our intuition. Just as children learn to talk without formal instruction, maybe they also intuit that part of their mind could exist apart from their body.
[Researchers] interviewed children from an indigenous Shuar village in the Amazon Basin of Ecuador. For comparison, [they] also interviewed children from an urban area near Quito, Ecuador. Both groups gave remarkably similar answers, despite their radically different cultures. The children reasoned that their bodies didn't exist before birth, and that they didn't have the ability to think or remember. However, both groups also said that their emotions and desires existed before they were born. For example, while children generally reported that they didn't have eyes and couldn't see things before birth, they often reported being happy that they would soon meet their mother, or sad that they were apart from their family. "They didn't even realize they were contradicting themselves. Even kids who had biological knowledge about reproduction still seemed to think that they had existed in some sort of eternal form. And that form really seemed to be about emotions and desires."
Why would humans have evolved this seemingly universal belief in the eternal existence of our emotions? [It] might be a by-product of our highly developed social reasoning. "We're really good at figuring out what people are thinking, what their emotions are, what their desires are." We tend to see people as the sum of their mental states, and desires and emotions may be particularly helpful when predicting their behavior. Because this ability is so useful and so powerful, it flows over into other parts of our thinking. We sometimes see connections where potentially none exist, we hope there's a master plan for the universe, we see purpose when there is none, and we imagine that a soul survives without a body.