In this blog post, we’ll examine the “costly signaling hypothesis”—one of several hypotheses that explain altruistic behavior—and use it to explore why people go so far as to help others even at their own expense.
“As long as it’s not me!” is a phrase often heard on variety shows. It refers to selfish behavior that benefits only oneself. The opposite of selfish behavior is altruistic behavior, which can be defined as “behavior that entails sacrifice or cost to the individual but benefits other members of the group.” Altruistic behavior appears to bring nothing but loss to the person performing it. Therefore, if we consider this purely from a theoretical perspective, the world should be filled with selfish people. However, in reality, there are many altruistic people who willingly sacrifice themselves for others. So why do people engage in altruistic behavior even at the cost of personal sacrifice? Various hypotheses have been proposed to explain people’s altruistic behavior today, including the kin selection hypothesis, the repeated reciprocity hypothesis, and the “birds of a feather” hypothesis. Among these, we will examine the “costly signaling hypothesis” to gain a better understanding of this behavior.
First, sending costly signals simply means self-display. It involves using certain behaviors to declare, “This is who I am!” Let’s look at an example. On the African savanna, gazelles live in herds. They are a primary prey species for lions, and an interesting phenomenon can be observed during a lion’s hunt. When a lion is about to begin hunting, most gazelles believe that fleeing is their only chance of survival and run away. However, there is one gazelle that doesn’t flee but instead begins to leap up and down right in front of the lion. It jumps vertically about 50 to 60 centimeters, as if to say, “I’m right here! Come and catch me.” This behavior is difficult to understand from a common-sense perspective. One might wonder why it would engage in an action that seems like a waste of energy when it could simply use that energy to run away faster. What’s even more interesting is that the lion shows little interest in the gazelle that’s jumping around as if to say, “Come and get me.” Instead, it pursues the gazelles that are running away with all their might. This gazelle has sent the lion a “costly signal” indicating its confidence in its running ability. And thanks to that signal, it can avoid being targeted by the lion without having to engage in an unnecessary chase. The value of such signals increases the more difficult the behavior is to perform—behavior that cannot be easily imitated by those lacking the necessary ability. Since anyone can send mere verbal signals, it’s difficult to convince others through words alone. Even if we assume the gazelle could speak and shouted, “I can run 100 meters in under 5 seconds!” the lion wouldn’t simply believe it and give up the hunt.
In this way, sending costly signals to others can increase one’s perceived value, which can be linked to why people engage in altruistic behavior. While altruistic behavior may seem to result in a loss for the individual at first glance, it actually conveys the message to others that “I am capable of providing this level of help.” In situations where it’s difficult to directly boast about one’s abilities, the most effective way to indirectly demonstrate them is by sending signals related to those abilities. This is where the “showing-off hypothesis” comes into play. On the other hand, people who lack ability may want to send signals, but since the cost of doing so outweighs the benefits they would gain, they end up abandoning the idea. Ultimately, only those with a certain level of ability can consistently practice altruistic behavior. In other words, the ability to engage in altruistic behavior also implies that one possesses the necessary capabilities and leeway to do so. Imagine a gazelle that isn’t a good runner jumping up and down vertically just to send a signal. Since this gazelle would end up revealing its lack of ability to a lion, it would be better off refraining from signaling.
Conversely, a gazelle that runs well will send a signal even while taking a risk, while a gazelle that doesn’t run well will flee as soon as it spots a lion. The lion targets the fleeing gazelle. In signaling games, this situation is called a “separating equilibrium,” a phenomenon that arises very naturally based on differences in ability.
Earlier, to understand why people engage in altruistic behavior that appears to bring them nothing but loss, we examined the “costly signaling hypothesis” among various theories. While this hypothesis is illustrated through the behavior of lions and antelopes, it can also be applied to explain behaviors such as purchasing luxury goods, driving expensive cars, and even engaging in minor displays of ostentation. Altruistic behavior may appear to be a loss on the surface, but even if it does not yield material rewards, it can demonstrate one’s abilities, financial stability, and character, thereby bringing benefits such as enhanced social reputation and standing. Ultimately, because acting altruistically can lead to positive outcomes for oneself in the long run, people choose such behavior; as a result, society is not composed solely of selfish individuals.
However, let’s consider some cases that often make headlines. When someone is in a life-threatening situation—for example, a drunk person who has fallen onto train tracks or someone trapped in a burning building—there are people who risk their own lives to save them. We call these people “civilian heroes.” However, if one’s own life is at risk in the process of saving someone in distress, the benefit of self-aggrandizement becomes meaningless. Nevertheless, there are certainly people who engage in such altruistic behavior. Therefore, the “costly signaling hypothesis” has certain limitations in fully explaining the behavior of these individuals.
