This blog post explores why worker bees risk their lives to protect the queen and how altruistic behavior evolved.
If worker bees could speak, you’d likely hear them say, “Protect the Queen!” Despite being unable to reproduce themselves, worker bees dedicate their entire lives solely to protecting the queen and her eggs. They care for the eggs laid by the queen and defend the hive, even sacrificing their lives when faced with external threats. They spend their entire lives sacrificing themselves for another individual. Thus, the role of worker bees in honeybee society extends far beyond mere physical labor. They function like a single organism, each performing their assigned task to ensure the survival of the entire colony. Crucially, the worker bee’s role is decisive in maintaining the order of the honeybee society and safeguarding the queen bee, who is responsible for reproduction, thereby guaranteeing future generations. However, this altruistic sacrifice poses a fatal threat to the survival of each individual. So why did altruistic behavior persist and evolve not only in bees but also in human and animal societies? To solve this puzzle, we need a compelling hypothesis—one being the kin selection hypothesis. This hypothesis explains how altruistic behavior evolved based on the fact that individuals related by blood share the same genes. Considering that relatives share genes, we can discover aspects of individual behavior we might not have previously considered.
Genes are the information that determines an individual’s traits, passed down from parent to offspring through generations. Individuals possessing genes advantageous for survival will prevail in competition, reproduce, and leave many descendants, while those with disadvantageous genes will gradually disappear. This is natural selection viewed from the individual’s perspective, as commonly understood by many. But what changes if genes are shared among these individuals? Generally, when organisms reproduce, offspring inherit genes from their parents’ sperm and eggs, so they share some genes with their parents. Siblings who inherit genes from the same parents also share genes. In the case of honeybees, particularly, since all sperm from the paternal side carry identical chromosomes, the degree of gene sharing among blood relatives is higher than in other species. The queen bee and worker bees share a high degree of 75%, while the queen’s eggs and worker bees share 50% of their genes. This represents a remarkably high level of genetic sharing even when compared to human societies. Thanks to this genetic structure, honeybees feel an instinctive responsibility for the survival of other individuals. Therefore, while a worker bee’s devotion to the queen and her eggs may be detrimental to the individual worker, it benefits the broader dissemination of the shared genes. Thus, the kin selection hypothesis explains that altruistic behavior evolved between related individuals because they share the same genes.
What significance does this altruistic behavior between kin hold when viewed from the perspective of genes? Biologist Richard Dawkins argued that altruistic sacrifice between individuals is selfish when viewed from the gene’s perspective. He viewed it as genes, not individuals, that compete to survive and increase their numbers, with individuals being mere survival machines manipulated by these genes. In other words, genes act to increase their own numbers rather than for the survival of the individual, making them selfish. If a gene a exists, an individual carrying gene a will strive not only for its own survival but also for the survival of other individuals carrying the same gene a. Viewing the world through this lens of the selfish gene allows us to better understand selfless acts between kin. Consider a scenario where enemies invade a honeybee colony, endangering the queen and her eggs, and a single worker bee sacrifices its life to save them. As mentioned earlier, due to the honeybee’s unique reproductive process, a worker bee shares 75% of its genes with the queen and 50% with her eggs. If a single worker bee sacrifices itself to save the queen and one egg, it effectively sacrifices 100% of its own genes to save 125% (75% + 50%) of the genes. Thus, from the perspective of the selfish gene, such behavior is entirely rational.
So far, we have examined how altruistic behavior, which could be disadvantageous from an individual’s standpoint based on the kin selection hypothesis, could evolve without being eliminated. However, the origin of altruistic behavior is not unique to honeybees or insect societies. In human societies, too, examples of self-sacrifice for family or close acquaintances are common. The kin selection hypothesis explains that altruistic behavior between kin, while disadvantageous to the individual, can be advantageous to the gene, thus allowing altruism to evolve. This is one of the most compelling, logical, and persuasive hypotheses that introduces the concept of genes to explain how altruistic behavior evolved. The kin selection hypothesis effectively explains aspects that other hypotheses, such as group selection, cannot account for. Of course, it has the limitation of not explaining altruistic behavior observed between unrelated individuals. However, this limitation can be addressed by explaining that individuals reciprocate favors only to those who have shown them favor, or that altruistic individuals group together to gain mutual benefits. Therefore, if we continue to develop the key to solving the puzzle of altruistic sacrifice, we may uncover the mysterious secrets behind the behavior of living beings, including humanity.
