When the concept of “death” emerged from the primitive human brain, it haunted us with two fundamental questions: Why do people die? Why do you die in this way?
| The novel “The Plague” by Albert Camus tells the story of a terrible plague in the city of Oran in Algeria. Father Panalu, a Jesuit priest, once preached that: “This plague is killing you,” he said, “it will also benefit you and guide you.” In another sermon, Father Panalu suggested: “The suffering of children is also our suffering. But without this suffering, our souls will die of hunger.” |
Charles Darwin, in his youth, was also perplexed by this question, and he thought he might have found the answer. In fact, his later arguments and Panalu’s sermons share a common point: death and suffering are certainly related to higher levels of “goodness,” although the goodness he referred to is different from the goodness mentioned by Panalu – the Jesuit priest provided this connection with spiritual and religious nurturing, while Darwin placed it within a magnificent biological evolutionary process.
He wrote this sentence in the final paragraph of his book “On the Origin of Species”: “Thus, the noblest goal we can imagine is the emergence of higher animal species, which appears right after natural wars, famines, and death.”
In a narrow sense, Darwin is completely correct: the idea embedded in the theory of natural selection is that life must pay the price of death. There is no poetic or sentimental meaning here, and it is unnecessary to think that our lives on this earth must be paid for with sorrow when we eventually depart. From a simpler and clearer perspective, the attributes we observe and evaluate from life, including accurate adaptation to the environment, complex body structures, and remarkable and diverse capabilities, all need to be built through a significant number of deaths.
This is a simple example; imagine a species consisting of 100,000 individuals living in the Garden of Eden with balanced resources. If each individual can only give birth to one offspring to replace itself in the population, nothing will change. But if species evolve, what would this Garden of Eden look like?
The idea embedded in the theory of natural selection is that life must pay the price of death.
It is believed that individuals born with a beneficial genetic mutation will help them adapt to the environment better than all the other individuals of the same age. For example, it may be better at hiding or finding prey faster, hunting more effectively, or engaging in battles more efficiently – whatever this mutation is, it will help it secure a position in the environment.
If the frequency of this new mutation increases from one in 100,000 to two in 100,000, then the individual carrying the mutation must have two offspring instead of one. But as I mentioned earlier, due to limited resources, the population size needs to be stabilized at 100,000. Therefore, when an additional individual carrying the new mutation enters the population, another individual without the mutation must die, thus creating space for the evolutionary process, if you will. Broadly speaking, each additional beneficial mutation requires an additional individual to die. In a population of 100,000, if the new mutation increases by 1%, then the number of deaths must increase by 1,000. If all populations share this new mutation, there will be an additional 100,000 deaths. Thus, the population has paid the price of death for the evolutionary process.
When adding more biological attributes to the “toy model,” the situation seems more serious. Almost all animal species are diploid, meaning they carry two copies of the gene set. Many new mutations are merely semi-dominant traits, meaning they compromise with another copy of the organism’s gene set and determine the organism’s behavior.
The great population geneticist J.B.S. Haldane proposed a simple mathematical model to estimate how many additional deaths a new beneficial mutation would spread in a diploid population. Using the aforementioned “toy model,” it can be inferred that throughout the entire history of evolutionary change, the number of additional deaths is approximately equal to the population size of any generation (100,000 individuals in the model).
The “additional” deaths mentioned here can also be called “good” deaths, because these deaths lead to an increase in the rate of beneficial mutations; from an evolutionary perspective, these deaths are not meaningless.
Setting aside the imagined and idealized 100,000 individuals, let us consider a real example. The most recent common ancestor of chimpanzees and humans was a species that walked on four legs. Its skeleton resembles that of modern chimpanzees; perhaps most importantly, their brains were roughly the same size as those of chimpanzees and significantly smaller than those of Homo sapiens.
Generally speaking, all the changes in the evolutionary process that transformed our human ancestors into modern humans are related to the increasing frequency of gene mutations in the primitive human population. So, in the transformation of the common ancestor of chimpanzees and humans into Homo sapiens, how many “kind” deaths did they have to pay?
We do not know how many mutations were created by natural selection during the transformation of the common ancestor of chimpanzees and humans into modern Homo sapiens. Based on the results of recent analyses of the genomes of humans and chimpanzees, scientists have conducted preliminary calculations and estimated the number of “beneficial” mutations selected from the common ancestor of chimpanzees and humans to the human lineage to be 100,000.
Based on estimates of species size and average generation time, as well as the total time since the divergence of chimpanzees from humans, scientists estimate the total number of deaths to be: 17.5 billion.
