Science and religion both offer origin stories of death.
It is tempting to set up religion against science in any discussion of life, death, and purpose. But religion and science are different kinds of things and one can find spiritual truths in both of them. Why we die is a question for which both offer an answer. Science answers in relation to the mechanics of life, which are based on the inferences we can make from material experience. Religions, to differing degrees, offer explanations for what lies beyond the curtain: they tell us about what we do not know, and sometimes cannot know, and must therefore take on faith.
Throughout history, there was a lot we didn't know. Religions provided God, in many forms, as an explanation for why things happened as they did. For many Christians, if God wanted them to know about something, it was in the Bible, and if it wasn't there, then they felt they didn't need to know.
Eventually, people started trying to figure out answers for themselves and death was taken out of the hands of God. Galileo was one of the kingpins of this let's-figure-it-out-ourselves movement. He and others developed the power of investigation to a fine art. Though it didn't always confirm what was written in religious texts, people drew confidence from the power of this approach. It explained death not as God's will, but partly in terms of things we could control. We discovered things like penicillin, C-sections, and immunization, all of which prevented deaths that in the past had to be accounted for by some divine malevolence.
In sum, we realized that in many cases, people's deaths were preventable. But to prevent them, we had to know the practicalities of why people died. We had to understand disease, trauma, development, and old age. Prayer, as far as anyone can tell, does not prevent death.
Eventually, everyone dies. So why do we have to die at all?
Religions offer answers. According to the Bible, Adam and Eve were punished with death by sinning against God (Genesis 3:17). As descendants of Adam and Eve, we share in their fate. Fair enough. But why do animals, like your dog, have to die? Did his ancestors eat from the doggy tree of knowledge? And trees die of old age too, which is just confusing. But maybe it's safer to say that God granted impermanence to all things as punishment for knowledge.
According to Islamic scholars, life is a test that ends with death: "Every soul shall have a taste of death and we test you by evil and by good by way of trial." (Quran 21:35). Christianity shares this judgment day vision as well.
Christianity and Islam are "other world" explanations for death. There are many of these kinds of religions. Norse mythology granted those who died well in combat an afterlife in Valhalla with Odin or in Frejya's field. In Greek mythology, the good passed to Elysian Fields. These other world explanations offer our lives as a transition from wherever we were before to a resting place beyond.
Some forms of Buddhism and Hinduism are variations on the other-world idea. They explain death as the end of a test, which is then followed by reincarnation. One's next life is determined by the quality of one's acts in this life. When one rises above the test, rising above preferences, one becomes liberated, finds nirvana, or is enlightened. This enlightened state isn't separate from this world, but it is a release from the suffering of this world.1
There is a nice example of this way of thinking in the Vedanta philosophy written down in the Upanishads. Here God is not above this world but is this world and everything in it. God is purple mountains and red Ferraris, politicians and dog poo. To be liberated is to realize that oneself and everything else is of the same fabric. Life as we often think of it, as divisions between you and I or one cult and another, are simply tricks we play on ourselves that keep us from understanding the true nature of God and reality. We think we die because God plays hide-and-seek with himself. But we never die, we just fall back into the wave of God. Alan Watts book On the Taboo Against Knowing Who You Really Are is an enjoyable romp through this way of thinking.
But religions don't really need to explain the details of life and death. Religions don't have to explain why sunsets are so absorbing. They don't have to explain why blue light refracts more than red light, thus making the sunset red. We can accept physical laws as God's preference if we like. The practicalities of our material experience obey their own laws and they lie where religions leave off. Where your experience and religion contradict, then it is up to you to investigate the conflict. Of course, you are allowed not to care. But no God worth believing in should reward you for something you never took the time to truly understand.
We can rely to a degree on our experience to understand the question of why we die and why we live. Born from the same line of thinking as Galileo's figuring-it-out-ourselves and Alexander Fleming's discovery of penicillin, our experience has a lot to say on these issues. You can consider science as a kind of empirical spiritualism, as it shares much in common with some of the religions described above. It is restricted to this material world because it is based on what we can infer from this world. Moreover, it provides a kind of practical knowledge that keeps people alive. Many people not only experience this empirical spiritualism in their life and work but believe it in their bones to be true. It is religious even if the church is no further away than simply paying attention to the reality of your life.
Science is one aspect of this experience. It is far from flawless, for all kinds of reasons. In part, it is based on the collective experience of millions of people who have tried to organize their knowledge in ways that help them understand the rules of this material world. Indeed, it is working together that led to the discovery of penicillin, immunization, the structure of DNA, how to split the atom, velcro, and so on. And it offers great insights into life and death.
So what does this collective knowledge of the material world tell us about death?
First of all, in one very real sense, it tells us we do not die. The cells that gave rise to you have been alive for millions of years, replicating over and over again, since life began some 3 billion years ago. You are alive and well everywhere there are cells. You can watch this replication for yourself on countless youtube videos. You as a product of these cell divisions share a common ancestry with all humans because the cell line that gave rise to us all has never died.
Even more beautifully, because all of life shares a common set of cellular mechanisms, many people believe that we share a common ancestry with all of life, including bacteria, weeds, meerkats and blue whales. Together, we are all one immortal life only divided from one another like a mother from her child.
You are ancient and everywhere.
the cells I am referring to above are called germ cells because they are capable of giving rise to individuals and they are different from the cells in the bodies of those individuals, which are called somatic cells, or soma. In most organisms, the germ cells are synonymous with eggs and sperm. But some cells that make up the bodies of individual organisms are immortal as well. Hydra is a multi-cellular water-dwelling organism that can regenerate its entire body from any portion of its cells. As far as we can tell, a Hydra never dies from old age.
Some cancer cells are immortal as well. Henrietta Lacks is the source of one of the most well-known immortal cell lines, which have continued to reproduce from her cancer cells long after she passed away (in 1951). Some estimates claim that laboratories have produced over 20 tons of her HeLa cells since her death. They have even been flown into space. HeLa cells have contributed to medical breakthroughs in cancer, AIDS, radiation and exposure to toxins. Her cells do not age and efforts have been made even to claim them as a new species.
Though our germ cells are functionally immortal (otherwise you wouldn't be here), our somatic cells (the stuff that makes up our bodies) does eventually wither and die like autumn leaves. Why is that? Evolution explains this death of our somatic bodies. In fact, it explains the death of all living organisms by explaining the length of their lifespans.
First, all organisms, even Hydra, sometimes die because the world is a nasty place. Predators gobble stuff up. Diseases lay waste to communities and populations. And the elements take their toll. Among wild mice, 90% die in their first year because of the cold. In the 1600s, mothers died in one out of a one hundred childbirths (now it is about 1 out of 10000).
Because most organisms don't live long enough to die of old age, cellular mechanisms required to keep them young and reproducing don't have a chance to evolve. For example, organisms like mice, most of which don't live past their first year, don't have mechanisms to deal with cellular stress in old age. So if you put a mouse in a cage and protect it from predators and the elements, it's cells will age rapidly after the first few years. Indoor cats, on the other hand, live about 15 years. If you had a pet Galápagos Giant Tortoise you could expect it to live more than 100 years.
Death by age-old seems to come not long after an organism's ancestors would expect to die by other means. This is called the disposable-soma theory. Personally, I think it would be more tasteful to call it the falling-leaves theory, as falling leaves are another form of disposable soma. The soma (or body) evolved to gather resources and reproduce. This occurs even at the cost of long somatic life because long life is hardly guaranteed in our rough and tumble world.
My body (this thing I narrow-mindedly call "myself") would not be here if my ancestors had not reproduced in time to keep our immortal germ cells dividing. In this sense, our bodies are the disposable but conscious eyes of a billion-eyed God. This is similar to the Vedantic philosophy I mentioned above. And some Christians might recognize the following words attributed to Jesus: "Split a piece of wood, and I am there. Lift up the stone, and you will find me there." If you are feeling less poetic, our soma is like the foam packing in a ceramic tea set delivered by post.*
To make the disposable-soma theory a little more practical, imagine a world like in the 1976 science fiction film, Logun's Run, where everyone is killed at age 30. In a world like this, there would be no anti-wrinkle cream, pension plans, or elderly care facilities. If someone did get lucky enough to grow old, they would have all kinds of problems that society simply never had a chance to work out. Evolution is the same way. It solves problems by facing them and producing varieties of solutions, some of which work and therefore persist and go on to produce even better solutions. Because of this, evolution cannot adapt organisms to experiences that they never encounter.
This problem of never living long enough in the first place leads to another source of our imminent demise called antagonistic pleiotropy. Antagonistic pleiotropy is the fact that some genes can produce multiple effects and these don't have to be all good. Hb-S is a good gene mutation that makes people resistant to malaria, but it also gives individuals with two copies sickle cell anemia.
Genes can have good-early effects but also have bad later effects. This trade-off between now and later is an ever present problem for any living system. Should you invest in reproduction now at the risk of dying sooner? This is what annual plants do. Should you take risks now to win a mate at the cost of damaging your long-term survivability? Many young males do this. Should you stay at home tonight and work to increase the future wealth of yourself and your (future?) offspring, or should you go to the bar to find that secret someone to help you make those offspring?
Species that die earlier for reasons besides old age lead to selection for genes favoring earlier reproduction. If that wasn't true, the species would go extinct wasting its resources keeping its somatic cells alive at the expense of reproducing its germ cells. If these genes have bad-later effects, evolution is unlikely to experience them and therefore can never select against them.
Another often proposed reason for death is mutation accumulation. This is simply the observation that cells acquire DNA damage over their lifespan. The evidence for this is mixed with respect to aging. However, mutations do shorten life and cancer from carcinogens is a case in point.
In a nutshell, our investigations into the natural world show that the life spans of organisms are calibrated to keep their germ cells alive and well. The mortality of our somatic bodies is the bargaining chip life uses to accomplish that.
Many people find deep spiritual wisdom in the universe from knowing that all of life shares a common origin. Many hold that even singling out living cells is an arbitrary distinction. Whatever it is that gives rise to us runs through life, the universe, and everything. The Buddhist philosopher Nagarjuna called it sunyata, or emptiness, which is to say that all things are empty of independent origination. It's really not a new idea.
Ultimately, the religious and scientific versions of why we die are different kinds of explanations derived from different ways of thinking about our existence. Setting them up against one another is a fool's game. Even within a single religion, there are many interpretations of sacred truths. Science is not so different: there are rarely single explanations for what we don't understand. Religions try to resolve this by pointing to sacred authorities or creating new branches of existing religions (sometimes agreeing to disagree). Scientists try to resolve this by collecting more evidence from our experience with the material world, enriching our understanding of ourselves and sometimes even prolonging our lives.
Religion and science serve their purpose in the world by enlisting our collective wisdom in the pursuit of lives worth living. For me, science and religion appeal to different aspects of life's problems. In the rare cases where they conflict, the part that is more speculative loses. As it should. The fewer people who experience a truth, the less likely it is to be true. That's common sense. Reality is far more interesting and beautiful than the stories we can communicate to one another, scientific or otherwise.
