The three male dolphins circle the female, separate her from the group and then usher her away. What we see here on the big screen in Michael Krützen's office on UZH's Irchel Campus is a fertile female dolphin being kidnapped by a group of males. This scene was filmed in Shark Bay, Western Australia. Shark Bay is a unique habitat with an exceptional density of marine life that includes dolphins, whales and turtles and, course of, sharks, from which the bay takes its name.
However, it is the dolphins that interest anthropologist Michael Krützen, who has been observing them since 1996. Two aspects of his research have made headlines in the scientific world: The animals' social behavior and their use of tools for foraging (see box). Now the question begs to be asked as to why an anthropologist is observing dolphins, when Krützen's subject is defined as the "science of human societies and their development".
What particularly interests Krützen about the dolphins is whether they show any form of human-like behavior that can be interpreted as a precursor to our behavior. The same approach was taken by Krützen's predecessor and director of the Department of Anthropology at UZH, Carel van Schaik, who researched orangutans for decades – with remarkable results. What Krützen can now report about the dolphins is no less groundbreaking – and, when it comes to intelligence, suggests perhaps an even closer link between these mammals and humans than the great apes, who are considered our closest relatives in the animal kingdom.
But back to the three males that have captured the female. They will then force her to stay with them, holding her hostage for up to several weeks. Romance often has little to do with it. "If the female tries to escape, the dolphins use brute force and deafening noises to stop her," Michael Krützen reports. This includes hitting her with their fins, banging her nose or producing a penetrating sound from their blowholes. While the female is in captivity, the dolphins mate with her on a rotating basis, each allowing the other to take his turn.
"The fact that the males cooperate in this way is unusual in the animal kingdom," says Krützen. "After all, we are dealing with a resource that cannot be shared – in this case, paternity." Although apes have been known to form coalitions to attack an animal of higher status, for example, it is generally the dominant males who can reproduce. This is not the case with dolphins, as genetic analyses show: "Paternities are relatively evenly distributed within the group, so no individual dolphin seems to be dominant," says the anthropologist.
When the male dolphins have nabbed themselves a female, their "ownership" over her does not go unchallenged for long. Since females who are ready to mate are in short supply, the male gang must constantly defend the female from challenges from rival gangs. This can lead to fights in which the animals cause harm to each other. When it's all over, the victorious males swim off with the female in tow.
And the females? At first glance, it appears that they are not in a position to decide for themselves with whom they wish to conceive their offspring. However, Krützen points out that the females want the best fathers with the best genes. The question therefore is whether they have developed a strategy against this form of organized group copulation. One trick the females could use to prevent an unwanted pregnancy would be to not become pregnant while being mated by males that do not suit them. During the mating season, which lasts from September to January, the females could potentially have several cycles. And that they could then allow themselves to conceive when a partner suited them. Whether this is the case, Krützen does not know at the moment. "Unfortunately, we cannot yet perform hormone analyses on wild dolphins that might answer that question."
Among the dolphins in Shark Bay, abducting females is commonplace. But what does that tell us about us humans? Well, reference to such behaviors certainly exists – in the Homeric epics, for example. And we know of sexual violence and its use as a perverse kind of strategy in contemporary civil wars. But does the anthropologist really see an analogy to us humans? Krützen declines to comment. He's more interested in something else – the fact that the dolphins form groups.
This is indeed exceptional, as the male dolphins bond while they are still young and then remain loyal to each other for the rest of their lives – unlike the females, who circulate in larger and less tightly-knit groupings. "Male dolphins form stable alliances of up to a dozen animals, sometimes more," says Michael Krützen. The basis of these alliances are childhood friendships between animals that grew up together but are not necessarily related. The important thing to note is that there are no male dolphins in Shark Bay who do not belong to an alliance. There is a simple reason for this: Without an alliance there are no females. To successfully reproduce, the male dolphins must belong to a group – and ideally to the right one, as some alliances are never without a female, and others more often, as Krützen's PhD candidate Livia Gerber has observed.
The formation of alliances between male dolphins is part of a complex social behavior symbolic of the dolphins of Shark Bay. This is because the dolphins exhibit forms of sociability that go over and beyond stable and established male groups. They live in what are known as open fission-fusion societies, i.e. societies in which the size and composition of the groups is constantly changing. With dolphins, this means that they meet, spend time together and then separate again. A kind of casual sociability that we humans also enjoy, says Michael Krützen. "People meet, drink a beer together, have a chat and then go their separate ways." And because dolphins build relationships within the structure of a wide, open network, the potential number of social contacts with whom they can interact over the course of a lifetime runs into the hundreds. Chimpanzees only form closed – and much smaller – groups of 30 to 40 animals.
Such open networks are extremely rare in the animal kingdom. For Krützen, it is clear that this type of complex interaction requires exceptional cognitive skills. Are dolphins therefore closer to us in this respect than great apes? Are they perhaps even more intelligent? "I wouldn't go that far," says Krützen. "But we see that dolphins have developed similar social behaviors to humans." And, of course, they count among the most intelligent creatures on our planet. "Evolution has produced three cognitive peaks: elephants, toothed whales, to which dolphins belong, and primates."
What distinguishes us from dolphins, elephants and other primates is the fact that we have cumulative culture and language. In contrast to most other animals, this enables us to pass on our cultural achievements to the next generation and thereby continue to develop, mainly thanks to our complex language.
The complex social behavior of the dolphins in Shark Bay may also be related to their special habitat, as the bay is rich in fish. The dolphins always have enough to eat and are under no pressure to migrate. As a result, they spend their whole life in Shark Bay. This has advantages: "The animals need little time and energy to search for food and therefore have more time for socializing," says Krützen. This combination of little stress and plenty of social contact probably also makes the dolphins more intelligent.
Michael Krützen goes on to draw a comparison with the orangutans in Borneo and Sumatra: "The apes in Sumatra live in larger groups and are cleverer when it comes to solving tasks. They also seem to have bigger brains." The anthropologist is convinced that this is linked to environmental conditions: Like the dolphins in Shark Bay, the orangutans in Sumatra enjoy an abundance of food, while their counterparts in Borneo have had to adapt to harsher environmental conditions due to dry periods of two to three years where food is correspondingly scarce. "The genomic studies that we published in 2018 show nicely which genes are subject to selection pressure," says Krützen. "The apes in Sumatra can invest in their brains, while those in Borneo have to be physically more robust."
It might be a similar case with dolphins. While those in Shark Bay wallow in the land of plenty, those living in less luxurious conditions are forced to invest more time and energy in their search for food, leaving fewer resources available for socializing. Krützen is testing this thesis on another population living further south in Perth. However, the data gained from his research so far does not suffice to make conclusive statements.
The research on dolphins and orangutans, which has been conducted for decades at the Department of Anthropology at UZH, shows how important such long-term studies are: "Being able to observe the animals over generations is crucial for us," stresses Michael Krützen. With the findings from this research, we have an answer to the eternally fascinating question: Is cooperative behavior unique to humans? For a long time, we believed that complex social behavior is only found in humans and – to a lesser extent – in great apes. Now we know that it is found in dolphins, too.