In this blog post, we’ll examine human altruistic behavior through the lens of the costly signaling hypothesis and explore how such behavior can be explained from an evolutionary perspective.
Altruistic Behavior Easily Found in Everyday Life
“The mistakes of humanity in the 20th century ultimately led to global poverty. Governments and economies around the world have completely collapsed, and amid this chaos, a mysterious rift in space-time is discovered. The remaining people must find this rift and save humanity in order to survive. To this end, a team of explorers is assembled. Leaving their beloved families behind on Earth, they embark on a journey from which there is no return—all for the sake of humanity.”
This is the plot of the movie *Interstellar*. The film, which gained immense popularity thanks to its stunning visuals, depicts the pilot “Cooper,” who sacrifices himself for the sake of humanity. Such self-sacrifice is a common theme in movies. The sight of someone risking their very life for the survival of the world touches many hearts and leaves a deep impression.
However, this act of giving everything for others is by no means confined to fictional narratives. In real life, it is easy to find people who sacrifice themselves for others, and such examples are frequently reported in the news and newspapers. There are cases like an elderly woman who donated her life savings to fund the education of underprivileged children, or a soldier who shielded his comrades with his own body from shrapnel when a grenade failed to detonate, saving their lives.
Looking at these examples raises a question. According to Darwin’s theory of evolution, only individuals best suited to their environment survive and reproduce successfully. Yet humans willingly accept personal loss through altruistic behavior. Even though such behavior does not seem to favor survival or reproduction, how did human altruism evolve and persist to this day?
An act that benefits others or society while incurring personal loss is called altruistic behavior. To explain this behavior, *The Banquet of Altruistic Humans* presents several hypotheses, one of which is the signaling hypothesis. According to this hypothesis, humans send signals to those around them through altruistic behavior to demonstrate their capabilities. The core of this hypothesis is that such signals enhance one’s image, and the benefits gained as a result further encourage altruistic behavior.
This hypothesis can also be applied to a scene from the movie *Interstellar*. Cooper is an exceptional pilot, and this skill is essential for piloting a spaceship that explores rifts in space-time. Therefore, it can be argued that by boarding the spaceship, he sent a signal demonstrating his abilities to others. As a result, his journey played a decisive role in leading humanity toward survival, and a space station named after him was built. Ultimately, his sacrifice was a signal, and through that signal, he received the reward of honor.
The Signaling Hypothesis Explaining the Evolution of Altruism
The most important point of this hypothesis is that sending a signal must necessarily entail a cost. The cost referred to here means the loss one incurs by performing a specific action. This includes not only simple monetary loss but also the expenditure of labor or physical energy. Furthermore, this cost must be sufficiently significant. Only when these two conditions are met does the hypothesis hold. This is because if anyone could easily send signals, even those lacking ability could act as if they were capable.
If the signaling mechanism functions properly, the result is as follows: For those lacking ability, the cost of signaling is very high. Therefore, since the cost far exceeds the benefit gained from signaling, they ultimately fail to send signals. Conversely, for capable individuals, the cost of signaling is relatively manageable. In fact, because the benefit gained from demonstrating their ability is greater, they send signals repeatedly. As this process continues, people come to believe that only capable individuals can send signals. Ultimately, signaling becomes an effective means of proving one’s ability.
Examples of the Signaling Hypothesis
This type of signaling can also be easily observed in animal ecology. A prime example is the relationship between lions and gazelles. The hunt begins the moment a lion spots a herd of gazelles. However, an intriguing scene unfolds at this point. While most gazelles run for their lives with all their might, some gazelles repeatedly perform vertical leaps right in front of the lion. At first glance, this is a very dangerous behavior that appears to offer themselves up as prey.
However, these high jumps have a clear purpose: they serve as a signal to the lion. From the lion’s perspective, targeting slow-running gazelles is the best way to increase its hunting success rate. However, it is difficult to judge which gazelles are slow based solely on their appearance until the lion actually gives chase. At this point, the high-jumping behavior exhibited by some gazelles serves as a signal to demonstrate their superior physical abilities. This is because the ability to jump vertically is closely related to running ability. In other words, they are actively showing that they are among the fastest individuals in the herd. This behavior is an example demonstrating that signaling strategies exist not only in humans but also in animals.
Such signals are also easily found in human society. The Aché tribe of Paraguay is a prime example. For them, hunting is a vital activity for the tribe’s survival. However, this tribe has a unique norm: those who do not participate in the hunt but eat the game brought back by others, or those who fail to catch prey, are not criticized. Conversely, boasting about one’s hunting skills is viewed negatively. Furthermore, the same members of the tribe consistently went out to hunt, while the rest of the tribe shared the food they brought back. Ultimately, this means that a select group of hunters continuously hunts for the benefit of the entire tribe.
This behavior can also be explained by the costly signaling hypothesis. In this tribe, the act of returning with a large amount of game serves as a signal to prove one’s exceptional hunting ability. While anyone can boast about their abilities with words—making such claims difficult to trust—the act of actually bringing back a large amount of game entails significant costs and thus serves as a reliable signal. Hunters who demonstrate their abilities in this way are known to gain an advantage when selecting a mate later on. Ultimately, the costly signaling hypothesis explains that even their altruistic behavior can, in the long run, be linked to their own self-interest.
Limitations and Significance of the Signaling Hypothesis
As such, even altruistic behavior that appears, at first glance, to have no direct connection to one’s own interests can be explained through the costly signaling hypothesis. Going to war for one’s country or showing consideration for others even in difficult situations can also serve as signals demonstrating one’s competence and trustworthiness to those around them. Ultimately, this series of actions can be interpreted as a process of communicating one’s invisible abilities and value to society.
However, there are limitations to relying solely on this single hypothesis to fully explain human altruism. This theory fundamentally assumes that only capable individuals can send costly signals. While it is true that altruistic behavior by highly capable individuals tends to receive greater attention in society, it cannot be assumed that all altruistic people possess sufficient ability or resources. This is because there are certainly people who willingly give to others even though they do not have much themselves. Furthermore, it is a stretch to interpret all of their behavior as merely a means to gain secondary benefits through signaling.
Therefore, to understand human altruism, it is necessary to consider not only the signaling hypothesis but also other evolutionary explanations. This does not mean that the costly signaling hypothesis loses its value. Rather, it holds significant importance in that various theories complement one another to provide a broader explanation of complex human altruistic behavior.
