The study’s findings reinforce the hypothesis that long-term memory in humans, chimpanzees, and bonobos likely originates from a shared common ancestor that lived between 6 million and 9 million years ago.
To investigate this, the research team utilized infrared eye-tracking cameras to observe the gaze patterns of bonobos and chimpanzees. The subjects were presented with side-by-side images, one of a stranger and the other of a bonobo or chimp they had cohabited with for a year or more.
The results revealed that the participants’ eyes lingered significantly longer on images of familiar individuals, indicating a degree of recognition. Notably, one instance involved a bonobo named Louise who hadn’t seen her sister, Loretta, or nephew, Erin, for over 26 years. When shown images of them, Louise’s eyes focused on the photos, suggesting a robust recognition despite the extended period of separation.
Lead author Laura Simone Lewis, a UC President’s Postdoctoral Fellow in Berkeley’s psychology department, emphasized the animals’ profound ability for recognition, highlighting the richness of their social memory. The study, published in the Proceedings of the National Academy of Sciences, sheds light on the enduring nature of nonhuman memory among our closest living relatives.
The study revealed that participants displayed a longer gaze duration at individuals with whom they had established more positive relationships, compared to those with antagonistic relationships. This suggests an ability to recognize friends more distinctly than foes, underscoring the complex nature of social memory in these primates.
Lead author Laura Simone Lewis emphasized that while the exact nature of the memory representation remains unknown, the study highlights the enduring nature of this recognition, persisting over years. The research underscores the similarities between humans and their primate relatives, challenging perceptions of how distinct our cognitive abilities are from other apes.
The findings contribute to the understanding of long-term memory in animals and raise intriguing questions within the realms of evolutionary biology and psychology. One prominent question is the origin of humans’ exceptional long-term memory and its potential links to the recall abilities observed in other species.
The study addresses a significant gap in the understanding of social memory in animals, expanding beyond previous knowledge. While prior research identified long-term social memory in dolphins, lasting up to 20 years, this study suggests that chimpanzees and bonobos may exhibit comparable or even longer durations of social memory.
The motivation for the research stemmed from the researchers’ observations of primate behavior, noting how these animals could seamlessly resume interactions after extended periods of separation. To validate this observation, the team embarked on a project that combined elements of genealogy and scrapbooking, seeking to unravel the mysteries of social memory among our primate relatives.
To initiate the study, researchers first needed to identify bonobos and chimpanzees that had experienced separation from their social groups, whether due to relocations to prevent in-breeding in other zoos or the loss of a sibling or elder within their shared living environment. With a list of such pairs spanning zoos in Europe and Japan, the next challenge was to obtain suitable photos representing the time of their last encounter.
Acquiring quality images, particularly for those separated in the mid-1990s like Louise’s relatives, proved challenging. Nonetheless, the team successfully gathered images for 26 bonobos and chimpanzees to include in the study.
To conduct the experiments, a computer system equipped with sensitive cameras and non-invasive eye-tracking tools was set up. The participating animals entered the room voluntarily, enticed by a reward of diluted fruit juice, a treat they enjoy in the wild. As they sipped their juice, the screens in front of them displayed pairs of images—alternating between a previous groupmate and a stranger—while the cameras monitored their eye movements. The data, capturing the duration of attention on each image down to a fraction of a second, provided valuable insights.
Lead author Laura Simone Lewis emphasized the simplicity of the test: whether the animals would gaze longer at the image of a previous groupmate or a stranger. The results revealed a significant preference for looking longer at pictures of their previous groupmates, showcasing their ability to recognize and remember individuals from their past social groups.
The researchers, initially concerned about potential stress reactions, observed that the participants did not exhibit signs of agitation. Instead, when shown images of a long-lost relative, some animals would even pause their juice consumption, seemingly captivated by the sight. This demonstrated a level of engagement and recognition that surprised and intrigued the research team.
The study, while shedding light on the recognition abilities of bonobos and chimpanzees, raises intriguing questions about the nature of their memories. The researchers are grappling with the uncertainty surrounding the type of memories involved—whether they resemble rich, episodic narratives akin to human experiences. Key questions include whether the animals harbor curiosity about why they are seeing these images and if they can extrapolate what their long-lost relatives might look like today.
Laura Simone Lewis, the lead author of the study, has returned to Berkeley as a postdoctoral fellow and plans to delve deeper into these inquiries. A Berkeley native, Lewis holds degrees from Duke University and Harvard University and has conducted a fellowship at the University of St. Andrews. Her co-authors include researchers from esteemed institutions such as Harvard, Johns Hopkins University, Kyoto University, the University of Antwerp in Belgium, and the University of Konstanz in Germany.
Lewis expresses a dual motivation for her work: a scientific curiosity driving her research and a commitment to conservation efforts for endangered bonobos. By understanding the cognitive abilities of our closest living relatives, she emphasizes the importance of protecting their habitats. The study serves as a reminder of the striking similarities between humans and other species on Earth and underscores the significance of conserving these remarkable animals.
Resources
- ONLINE NEWS University of California – Berkeley. (2023, December 18). Chimps and bonobos can recognize long-lost friends and family for decades, find researchers. Phys.org. [Phys.org]
- JOURNAL Lewis, L. S., Wessling, E. G., Kano, F., Stevens, J. M. G., Call, J., & Krupenye, C. (2023). Bonobos and chimpanzees remember familiar conspecifics for decades. Proceedings of the National Academy of Sciences, 120(52), e2304903120. [PNAS]
Cite this page:
APA 7: TWs Editor. (2023, December 19). Researchers Find That Chimps and Bonobos Have Long-Term Memory of Friends and Relatives. PerEXP Teamworks. [News Link]
