Human beings are altruistic, some vampires too

Human beings share food and other goods. We are, or can be, altruistic. We are not with anyone, or under any circumstance, but it is a habitual behavior. That’s why it seems normal to us, although, to tell the truth, it should surprise us, at least from an evolutionary point of view. Altruistic behavior entails giving up a competitive advantage in relation to other members of the group or even reversing it.

Three possible reasons are usually considered for which it may be worth being altruistic. On the one hand, there is the selection by kinship, by virtue of which it is advantageous to be so with the people (relatives) with whom a part of the genes are shared because, helping them, it is facilitated that a part of the genetic patrimony lasts.

It can also be (especially when food or other goods are shared) by freeriding tolerated (or consented). It occurs when those who have food are unable to monopolize it due to the costs imposed by those who do not have it. Although the latter do not force you to share it, they can make it very expensive for you not to do so.

Third is reciprocity: whoever has food or another valuable asset today may have received help from another in the past or may need it in the future. That is, it would be advantageous to share food in situations where reciprocity on the part of the recipient may turn out to be convenient in the future for the sharer.

To the three previous reasons, we must add a fourth mechanism that can lead to behaving generously. Altruism and, in general, prosocial behavior, can also be a consequence of the selection at the cultural group level. Groups in which norms favoring cooperation are developed and transmitted compete advantageously with those in which such norms are weaker or less far-reaching. Prosocial behaviors may therefore be the result of a process of cultural (or genetic-cultural) evolution in which selection does not operate only on the gene or the individual, but also on the group. This modality is probably exclusive to hypersocial species, like ours.


We are not the only primates who share food. The first three reasons mentioned in the previous paragraphs seem to be at the base, too, of the generous behavior of other primates, such as chimpanzees, bonobos, capuchins and tamarins. The two reasons that influence the most are consented freeloading and reciprocitywhile that of kin selection is somewhat lower.

In the human species, the differences between populations in the degree of reciprocity of their members seem to be related to the level of predictability of the amount of food available. In those where the possibility of having food on a regular basis is more uncertain, reciprocity tends to be more important.

altruistic vampires

Altruism is not limited to primates either. Desmodus rotundus feeds on blood: it is a real vampire, that is, a blood-sucking bat. In addition, he shares the blood he obtains with other vampires of his own group.

Through experiments designed for this purpose, it has been possible to verify that, by sharing blood, bats of this species establish lasting bonds with their congeners, by virtue of which they adopt the habit of sharing food among themselves. The individuals with whom they do so may or may not be from the same family, so it does not seem that their altruism is due to kin selection. On the other hand, given the special way of sharing blood –regurgitating it–, this behavior cannot be explained by tolerated freeloading.

In Desmodus rotundus there is reciprocal altruism. When a vampire gives part of his food to another and thus establishes a bond with him, both benefit from that relationship. Because sometimes it is one that manages to feed itself and other times it is the other. With this behavior, the probability of deprivation in an environment of uncertain feeding possibilities decreases for both.

The small amount of blood that is shared on each occasion can represent, for the person who receives it, the difference between reproducing or not, or between surviving or dying, while the person who donates loses only a part of what they have achieved. For this reason, altruism has a very high adaptive value in these animals –which are also social. The continuity of the entire group depends on it.

Human beings are altruistic, some vampires too