C.2: How Can Human Behavioral Ecology Help Us Understand Altruism?

Altruism is defined as providing a benefit to someone without expecting anything in return. A perfect example is donating money to tsunami victims. From an evolutionary perspective, it seems that providing benefits to others would be disadvantageous for one’s own survival and reproduction, as resources given to others are resources that cannot be used for oneself. But people do engage in altruistic behaviors, so how can the field of human behavioral ecology help us understand this behavior? We will use the example of food sharing to think about different ways that human behavioral ecologists have examined this question. In many small-scale hunter-gatherer societies, people share food extensively with other people living in their communities. This sharing is most widespread when the item is a hunted animal, which can typically feed many people. Just as giving away money seems counterintuitive, so does giving away food. So, why do people in these foraging communities share so much food with each other?

Kin Selection

One of the first explanations for why humans share food is that they are sharing with their close family members. Kin selection proposes that individuals help kin, even at a cost to themselves, because this help is directed at individuals with whom they share genes. Genes that result in a person acting altruistically toward close kin would have become more frequent over time if individuals sharing that gene are more successful than those not sharing that gene (Hamilton 1964). Taking this perspective is described as a gene’s eye view. Since family members share genes, this may explain why kin help one another. Figure C.4 shows a Lao family eating together. It is very common around the world for families to share food with one another. In many small-scale societies, people share food with family members but also with those who are not family members. Kin selection helps explain some food sharing, but it doesn’t explain all food sharing.

Figure C.4: Lao family eating together. Credit: Lao Mangkong family eats together by BigBrotherMouse is modified (faces blurred) and under a CC BY-NC-SA 4.0 License.

Reciprocal Altruism

Another potential explanation for why humans share food is that they are engaging in reciprocal altruism, meaning that an individual shares food today with the expectation of repayment at some point in the future (Trivers 1971). This can work well, unless the person who receives the help chooses not to reciprocate in the future. In this case, the original sharer does not obtain anything in return. To maintain these relationships, it is important that individuals have the opportunity to share with one another repeatedly and that if one person chooses not to reciprocate, the original sharer terminates their sharing.

Reciprocal altruism is even more likely to occur if the value of the food is greater to the person receiving the food than the person sharing the food. For instance, imagine that you have an entire pizza. After you eat several slices, you are no longer hungry and the next piece of pizza has little value to you. In contrast, if you are hungry, receiving a slice of pizza from a friend would mean a lot to you. In this case, the person giving a piece of pizza after already eating their fill is giving away something of little value, but the person receiving a slice of pizza when they are hungry is receiving something with substantial value. If the following week the roles are reversed, then in both cases, the person receiving the food has received something of greater value than the person who gave it away.

Figure C.5: A Lamalera whale-spearer jumps from a boat, spearing a whale in Lembata Island, East Nusa Tenggara Province. Credit: Lamafa (spearer) jumping from peledang boat to a whale by Bambang Budi Utomo is in the public domain in Indonesia.

This makes sense in the case of sharing hunted meat as well. In environments without refrigeration technology or in highly mobile groups where food storage is not feasible, the killing of a large animal will result in leftover meat. Sharing that meat with hungry community members has a lot of value to those receiving the meat. Then, at some point in the future, the person who received the meat may successfully hunt and share with others. Figure C.5 displays an Indigenous hunting party from Malaysia. Food is widely shared in small-scale societies, particularly when the item is large in size and when there is a lot of uncertainty around when the next successful hunt will occur (Gurven 2004). But, as with other skilled activities, some individuals are better hunters than others and acquire more meat than others consistently, so why would highly skilled hunters give more food to low-skilled hunters than will be reciprocated (e.g., Gurven et al. 2000)? Again, reciprocal altruism is one piece of the story but cannot explain all sharing behavior.

Costly Signaling

Another possible explanation for why people share food, particularly meat in small-scale societies, is because they want to signal their foraging abilities and generosity (Smith and Bliege Bird 2000). One way to communicate to others your inherent qualities is to do something that is hard to fake. For instance, telling someone that you are a good hunter is not as convincing as hunting a difficult-to-acquire animal and sharing it with them. If someone is a poor hunter, it will be difficult for them to successfully hunt, so sharing hunted meat demonstrates one’s abilities. The hunter who provides resources to the community is likely viewed as generous, allowing them to attract mates, friends, and allies. Costly signaling theory argues that a signaller produces a costly display (e.g., shares hunted meat) to communicate honest information about themselves to others (e.g., I am a generous, skilled hunter). Costly signals can occur across species for a variety of purposes, but this example may help us understand why people share food with unrelated others who are unlikely to reciprocate.

Figure C.6: Green turtle. Credit: Green turtle Palmyra Atoll National Wildlife Refuge by Kydd Pollock, The Nature Conservancy, US Fish and Wildlife Service Pacific Region is under a CC BY-NC 2.0 License.

Among the Melanesian Meriam Islanders, turtles (Figure C.6) are hunted at two times of year; during the turtles’ feeding/mating season, which is risky and unpredictable, and during the turtles’ nesting season, which is low risk and relatively easier. Turtles hunted during the feeding/mating season are typically shared widely in the community, while turtles hunted during the nesting season are consumed by a small number of households. This suggests that more people know about high-risk hunts, which may result in hunters gaining more prestige for their successful hunts. Evidence also shows that hunters involved in high-risk hunting gain social and reproductive benefits, such as having children earlier and having more sexual (or reproductive) partners (Smith, Bliege Bird, and Bird 2003). While some sharing behavior may be best explained by a desire to display one’s skills to gain reputational benefits, it cannot explain all sharing behavior and likely works in conjunction with the other hypotheses described above.

What Does Food Sharing Tell Us about Altruism?

Examining these three explanations of sharing behavior—kin selection, reciprocal altruism, and costly signaling (Figure C.7)—helps explain a lot of sharing seen around the world, but donating money to tsunami victims is still hard to understand. Most donors from the United States were not related to the victims of the tsunami; donors probably did not expect reciprocation; and because the donors and receivers did not know each other, reputational benefits would have been limited to people who were made aware of the donation. While some charitable giving may be explained by the tax incentives, the donations to the tsunami victims were so extensive that it seems unlikely to be the main explanation. There are other hypotheses that have not been discussed here, but they also suffer from the inability to fully explain all examples of altruistic behavior. People commonly state that they donate because “it makes them feel good.” While helping others does make people feel good, this likely evolved because those that had the feel-good sensation helped others (like their family members) resulting in greater survival and reproduction. The “feel good” sensation is a proximate explanation, the immediate reason for the behavior, while human behavioral ecology seeks to understand the ultimate explanation, the deep evolutionary reason that this trait led to increased survival and reproduction. In the case of donating money to people living on the other side of the world, our modern environment (allowing us to help people living so far away) may lead us to act in ways that were adaptive in our evolutionary past but may not improve our survival or reproduction today.

Explanations of food sharing:

1. Kin selection: Helping family members who share the same genes.
2. Reciprocal altruism: Sharing food with someone with the expectation that they will reciprocate at some point in the future.
3. Costly signaling: Providing food to others to display one’s foraging skill and generosity to improve one’s reputation or social standing.

At the same time, we struggle to solve the problem of homelessness across the United States. Using evolutionary theory may help us understand why people are unable to come together to eliminate this problem. Eradicating homelessness would be costly, would require the cooperation of lots of individuals (no single individual or small group can solve it on their own), and would be ongoing. This type of long-lasting commitment to help unrelated strangers may be difficult to acquire from large numbers of people.