More than a century ago, a small group of chimpanzees helped revolutionise the way scientists understood intelligence. Through a series of pioneering experiments on the Spanish island of Tenerife, these apes demonstrated that they could solve problems using insight rather than relying solely on trial and error – a discovery that challenged long-held assumptions about the uniqueness of human reasoning.Yet, while their scientific achievements became famous, the fate of the chimpanzees themselves remained largely overlooked. According to Dr. Javier Virués-Ortega’s study, “The Fate of Sultan’s Clan,” published in the journal European Psychologist, newly examined archival records reveal what happened to these famous chimpanzees after they were transferred to Berlin.
The chimpanzees that changed psychology
The Prussian Academy of Sciences established its anthropoid research station in Tenerife in 1913, and German psychologist Wolfgang Köhler served as its director from 1914 to 1920. During this period, he carried out the pioneering experiments that would reshape scientific understanding of animal intelligence.To answer this question, Köhler designed a series of experiments involving a group of chimpanzees that included Sultan, Rana, Chica, Grande, Tercera and Tschego. Instead of teaching them through repeated rewards, he presented them with unfamiliar problems that required planning and creativity. In one of the most famous experiments, bananas were suspended out of reach while wooden crates were scattered around the enclosure. Rather than making endless unsuccessful attempts, some of the chimpanzees stacked the boxes to create a platform and climbed up to retrieve the fruit. Another landmark experiment involved sticks placed near food that lay beyond the animals’ reach. Sultan famously realised that two short sticks could be joined together to make a longer tool capable of pulling the food closer. These solutions appeared to emerge through sudden understanding, or “insight,” instead of gradual trial and error. The experiments became milestones in comparative psychology and helped establish that chimpanzees possess sophisticated cognitive abilities, fundamentally changing scientific thinking about animal intelligence.
The skull of the chimpanzee named Rana-Loca (Image Credit: Javier Virués-Ortega via University of Auckland)
From scientific stars to forgotten lives
Although Köhler’s experiments became world-famous, the later lives of the chimpanzees received little attention.When the Tenerife research station closed in the 1920s, the six surviving chimpanzees were transferred to the Berlin Zoological Garden. For decades, historians knew very little about what happened after their arrival.The new research pieces together their fate using zoo records, correspondence and other historical evidence. The findings reveal that life in Berlin was far removed from the carefully managed research environment in Tenerife. Born in the tropical forests of Cameroon, the chimpanzees struggled to adapt to Berlin’s harsh winters. The zoo also faced severe financial difficulties after World War I, resulting in inadequate heating and a poor starch-heavy diet of bread and potatoes instead of fresh fruit. Combined with illness, pregnancy and social upheaval within the group, these conditions are believed to have contributed to the premature deaths of several chimpanzees.The researchers also rediscovered the preserved remains of several members of Sultan’s clan at Berlin’s Museum für Naturkunde, where they had remained unidentified for decades. Modern DNA analysis of these remains may help researchers better understand the chimpanzees’ origins and genetic relationships, while preserving an important part of psychology’s history.The study also documents how the chimpanzees endured the economic hardships of the interwar period, which further affected conditions at the Berlin Zoo. Their welfare steadily declined, and one by one, the chimpanzees that had once helped reshape psychology disappeared from the historical record. Only later did researchers begin reconstructing their forgotten stories through archival evidence.
Why their legacy still matters
The researchers argue that remembering the chimpanzees’ lives is just as important as celebrating the scientific breakthroughs they made possible.Today, studies continue to show that chimpanzees use tools, cooperate with one another, plan ahead and display complex social behaviour. Many of these discoveries build upon the foundations laid by Köhler’s pioneering work on Tenerife.However, the new historical investigation reminds us that scientific progress often depends on living animals whose welfare deserves equal attention. By tracing the lives of Sultan’s clan beyond the laboratory, the researchers highlight the need to acknowledge not only their role in advancing knowledge but also the hardships they experienced after the experiments ended.More than 100 years later, the story of Sultan, Rana, Chica, Grande, Tercera and Tschego serves as both a landmark in the history of psychology and a powerful reminder of the ethical responsibilities that accompany scientific research. Their remarkable intelligence changed how humans think about the minds of other animals, while their largely overlooked final years underscore why compassion and animal welfare must remain central to modern science.