Chimpanzees are better at reasoning than we thought

{"text":[[{"start":null,"text":"

"}],[{"start":7.73,"text":"The writer is a science commentator"}],[{"start":11.18,"text":"We humans hold beliefs about the world — and, for the most part, are happy to update those beliefs in the light of fresh evidence. That capacity to reflect on what we know and how we know it, and to act accordingly, is widely considered a hallmark of human rationality."}],[{"start":31.27,"text":"Our species is not alone in this regard, scientists now claim. Researchers have shown that chimpanzees can also change tack after weighing up different types of evidence. The experiments involved the animals judging which of several containers held food, having been given sequential clues of varying persuasiveness. The study was published in the journal Science last month."}],[{"start":60.16,"text":"According to an accompanying commentary, the animals consistently made rational choices two or three times more often than non-rational ones across the experiments. “These findings demonstrate that nonhuman apes have a spontaneous ability to weigh evidence of varying strengths, revise prior choices, and adapt when evidence is revealed to be unreliable,” wrote Brian Hare, an evolutionary anthropologist at Duke University in North Carolina, who was not involved in the study."}],[{"start":96.34,"text":"The finding, which builds on previous less conclusive work by others, tells us something important: the great cognitive shift that allowed humans to reason about the world is also present to some degree in our closest non-human relatives, as the 19th-century English naturalist Charles Darwin always suspected. "}],[{"start":122.07000000000001,"text":"The international research team was led by Hanna Schleihauf from Utrecht University and involved observing animals at the Ngamba Island Chimpanzee Sanctuary in Uganda. In the first of a series of experiments, each involving up to 23 animals, a chimp was shown a piece of food that was subsequently hidden in one of two containers."}],[{"start":148.4,"text":"The animal was then offered an initial clue about that morsel’s location. That first clue could be strong, such as seeing it inside a container with a transparent window. Less direct initial hints included the container being rattled, suggesting something inside, or traces of food behind the container."}],[{"start":172.85,"text":"After the chimp had chosen, it was then shown other evidence about the boxes — sometimes stronger than the first clue, sometimes weaker — and offered the chance to switch. The chimps behaved exactly as expected if they were indeed weighing evidence in a rational way: they stuck with their first choices when the initial clue was strong and the counter-evidence underwhelming; but were more likely to switch when given weak evidence first and subsequently a strong clue that the food lay elsewhere. "}],[{"start":210.49,"text":"Other ingenious variations on this hide-and-seek game, sometimes involving three containers, suggested the chimps could tell the difference between old and new information: they tended to ignore repetitions of the same rattle but reconsidered if the rattle was followed by a dropping sound, as if a second morsel had been dropped into the box. They soon wised up to misleading clues, such as pictures of food painted on a container."}],[{"start":244.87,"text":"The authors conclude: “Chimpanzees did not attribute a fixed value to each type of evidence; instead, they weighed the relative strength of evidence.” The work, they claim, strongly supports the idea of the animals possessing “genuine metacognitive capacities”, able to juggle concepts like hypotheses, evidence and causal connections."}],[{"start":269.32,"text":"That finding, that chimpanzees can think about thinking, puts Pan troglodytes in closer cognitive proximity to Homo sapiens than ever before. Such a conclusion is unlikely to have surprised the late primatologist Jane Goodall, who co-founded the sanctuary housing the chimps used in the study and who so often unmasked the similarities, such as tool use, between ourselves and other species.  "}],[{"start":299.52,"text":"Neither would it have shaken Darwin, who coyly sidestepped the question of human evolution in On the Origin of Species but addressed it later in The Descent of Man. There, Darwin describes taking a live snake to the monkey house at London’s Zoological Gardens, and observing as “monkey after monkey, with head raised high and turned on one side, could not resist taking a momentary peep into the upright bag, at the dreadful object lying quietly at the bottom”."}],[{"start":335.26,"text":"It confirmed simian curiosity of “a most human fashion”, adding to Darwin’s radical conviction there was “no fundamental difference between man and the higher mammals in their mental faculties”."}],[{"start":351.19,"text":"More than 150 years later, and amid deeper scrutiny of our fellow primates, science is still chipping away at our status as the greatest of great apes."}],[{"start":365.48,"text":"Letter in response to this column:"}],[{"start":368.61,"text":"Perhaps we can take a cue from chimps’ behaviour / From Avinashiappan Myilsami, Post Graduate Teacher, Sulur, Tamil Nadu, India"}],[{"start":389.27,"text":""}]],"url":"https://audio.ftcn.net.cn/album/a_1763422566_6343.mp3"}