Episode Summary
Executive Summary: APA host Kim Mills interviews Dr. Laura Simone Lewis about chimpanzee and bonobo social cognition. Lewis explains that these apes, our closest living relatives, can recognize former groupmates after years apart, show heightened attention to socially close individuals, and display social curiosity similar to human children. The conversation explores methods, comparative findings, and what ape behavior reveals about the evolution of human memory and social intelligence.
Main Topics: Human–great ape evolutionary relationship (Priority: 5/5): Lewis situates chimpanzees and bonobos as our closest living phylogenetic relatives, emphasizing shared ancestry and near-identical DNA as the basis for studying similarities and differences in social cognition. Long-term social memory in chimpanzees and bonobos (Priority: 5/5): A key study used eye-tracking to show that both species look longer at photos of former groupmates than strangers, with especially strong attention to previous friends. Social relationship strength shapes attention (Priority: 5/5): The apes’ attention was not just to familiar faces generally; they paid more attention to individuals with whom they had had more positive social interactions. Methodology and ethical considerations (Priority: 4/5): Lewis discusses non-invasive eye tracking, neutral-expression photos, and careful monitoring to avoid harm or distress in endangered great apes. Social curiosity in children and chimpanzees (Priority: 4/5): A separate study using “curiosity boxes” found that both children and chimpanzees prefer watching social interactions over lone individuals, suggesting a shared motivation to extract social information. Developmental and gender differences in children (Priority: 4/5): Children’s curiosity diverged around age five: girls increasingly preferred positive social interactions, while boys increasingly attended to negative/conflict situations, possibly reflecting both socialization and evolutionary pressures. Future research and broader evolutionary implications (Priority: 4/5): Lewis argues that comparing humans with apes helps reveal how social intelligence evolved, and previews new lab work on friendships, infants, and maternal social relationships.
Key Arguments: Chimpanzees and bonobos are close enough to humans—evolutionarily and cognitively—that their behavior can illuminate the origins of human social intelligence. Long-term recognition in apes is not limited to novelty detection; social relationship quality affects memory and attention, especially for prior friends. The eye-tracking evidence suggests apes process photos as representations of real individuals, not merely as abstract images. Positive social bonds appear more salient than negative conflict in long-term social memory for both chimpanzees and bonobos. Humans and chimpanzees both show a preference for gathering information from social interactions rather than solitary action, indicating a shared social curiosity. Children’s gender differences in social curiosity likely reflect an interaction between socialization and evolved predispositions rather than a single cause. Studying apes requires indirect, creative methods because researchers cannot ask them verbally about their thoughts; behavioral paradigms are necessary proxies. Comparative research is most informative when it asks what makes humans similar to great apes, not only what makes humans unique.
Data Points: Time since last common ancestor with humans: 5 to 9 million years ago - Lewis describes when humans and chimpanzees/bonobos last shared a common ancestor. Shared DNA with chimpanzees/bonobos: almost 99% - Lewis emphasizes genetic closeness to justify behavioral comparisons. Longest bonobo social memory reported: 27 years - Bonobo Louise appeared to recognize her sister and nephew after nearly 27 years apart. Typical face-memory span in several species: up to 3 years - Lewis cites prior findings for dogs, macaques, elephants, sheep, and orangutans. Bonobo vocal recognition span: up to 5.5 years - Previous research showed bonobos recognizing vocalizations of former groupmates for years. Dolphin vocal recognition span: up to 20 years - Lewis references a study on dolphins’ long-term vocal memory. Eye-tracking social cognition sample finding: significantly longer looking at former groupmates vs strangers - Main experimental result in chimpanzees and bonobos. Social-preference effect: longer looking at former friends than former non-friends - Apes attended more to individuals with higher rates of positive social interactions. Group size: up to 150–200 individuals - Typical community size for chimpanzees and bonobos in fission-fusion societies. Curiosity-box spacing: about 3 feet / 1 meter apart - Design detail of the human-child/chimpanzee social curiosity experiment. Age of curiosity split in children: around 5 years old - Girls and boys began diverging in preferences as they entered school and increased socialization. Age by which sex difference was significant: 6 years old - By age six, girls preferred positive interactions and boys preferred negative interactions more strongly.
Pivotal Quotes: "“We share almost 99% of our DNA with them.”" — Dr. Laura Simone Lewis: Used to explain why chimpanzees and bonobos are so informative for understanding human evolution. "“What I found and I was shocked by is that sometimes the chimpanzees and bonobos in this study would be drinking juice ... and just stare with their mouths hanging open.”" — Dr. Laura Simone Lewis: Anecdotal description of animals’ apparent recognition response during the eye-tracking task. "“What makes humans so similar to our great ape cousins?”" — Dr. Laura Simone Lewis: Lewis reframes the comparative research question from human uniqueness to shared evolution.
Implications: The findings suggest long-term social memory and social curiosity are not uniquely human. They also support using apes as models for the evolutionary roots of memory, attention, and relationship processing, with relevance for animal welfare and future comparative cognitive research.