TR How did you become a primatologist? 

JY I was at high school and university during a time when student movements were sweeping across the world, and I harboured significant doubts about what it meant to be human and what society truly was. While grappling with the thought that the answers couldn’t be found in past ideologies, I encountered primatology, a field that involves stepping outside of humanity to re-examine the world. I felt, “This is it.” 

TR Do you think apes love each other? 

JY That depends on the definition of love. If love is defined as “thinking about the other person and devoting oneself to them without considering one’s own interests”, then I believe there is love between ape mothers and their offspring, fathers and their offspring, and even between certain males and females. 

TR What does your study of primates teach us about human society? 

JY From a biological perspective, human society is not fundamentally based on male-female pairs. Instead, the foundation of human society lies in a multilayered structure where multiple family-based groups come together to form a community. This structure is made possible by a high capacity for empathy and cognition, and it emerged after humanity moved from tropical rainforests to the savannahs. 

TR What is particular about Japanese primatology? 

JY The method of identifying individual animals by giving each one a name and recording all social interactions, known as the “Japanese method”, is a distinctive feature. Initially, Western scholars criticised this method as being anthropomorphic. However, it was later reassessed when it became clear that non-human primates also possess sophisticated social structures and proto-cultural behaviours.

TR Is it meaningful to talk about community in the context of primates?

JY Multilayered social structures are rare among non-human primates. For example, hamadryas baboons and gelada baboons form large groups of several hundred individuals by aggregating multiple one-male units, but they’re essentially just gathering together. In contrast, humans form multiple groups within a community that extend beyond family units. Furthermore, as individuals move, they create groups and connections that transcend communities. This is possible because individuals can freely enter and leave groups. Non-human primates, on the other hand, cannot rejoin their original group once they leave it. This is because they belong to groups to maximise their own benefits, whereas humans are willing to sacrifice their own interests for the sake of the group. 

TR Is there an anthropomorphic desire to see human forms reproduced by primate communities? 

JY I believe that the human family began with the societal establishment of the father figure, so I focus on how fatherhood is created among gorillas. Additionally, to consider what communication might have been like before humans began speaking, I pay attention to the fact that while monkeys cannot engage in face-to-face communication, great apes can. Human conversation also likely began with face-to-face interaction, and I theorise that the development of visible sclera [the whites of the eyes], which great apes lack, allowed humans to read each other’s feelings through eye movements.

TR How do primate communities challenge our preconceived notions of the ways in which we relate?

JY Our social cognitive abilities developed in a time before language existed. This is known as mentalising – the ability to infer and interpret the mental states of others and to understand actions flexibly in context. This skill develops from around the age when the brain reaches its full size, between 12 and 16, and continues until about 25. However, there is a possibility that the generation heavily reliant on language and symbols through social media may lack this ability at present. 

TR What has your work taught you about the interplay between the cultural and biological qualities of humankind?

JY Humans have built societies by leveraging their biological forms and physiology while embracing cultural and spiritual elements. For example, they have utilised musical voices as a foundation upon which they constructed linguistic logic, enabling groups to overcome hardships that individuals alone could not surmount. Humans have expressed emotions and awareness such as love through words, incorporating relationships between parents and children, as well as between men and women, into the fabric of society. Efforts have been made to eliminate inequality and discrimination through ethical principles expressed in language. Clothing, food, and housing, within each culture, serve as frameworks that shape human relationships and represent social values. 

TR How does primate communication inform our understanding of social interaction in general?

JY Non-human primates can build societies without language. However, all diurnal primates build societies based on visible phenomena. Phenomena captured by other senses – like hearing, smell, taste, touch – are recaptured by sight, their meaning understood and placed in society. Humans have also followed this approach, but through language and other representations, they have started to build society based on what they cannot see – or imagination. 

TR How does interspecies violence figure in your research? 

JY Both gorillas and Japanese monkeys have basically no natural enemies, except for humans. I have studied the relationship between gorillas and chimpanzees in the areas where they coexist [Kahuzi, Democratic Republic of Congo and Moukalaba, Gabon], and they basically do not encounter each other. There is significant overlap in food and range, particularly in the common consumption of fruit, but they change their foraging patterns to reduce the chance of encounter, and they feed on different fallback foods to each other when fruit is scarce. 

TR How do you see the future of human-primate engagement? 

JY Ecotourism and nature-positive living are key for this relationship. Today, when machine civilisation has taken human life away from nature and placed a heavy burden on the earth, people are beginning to search for an earth-friendly way of life again. The wild lives of human neighbours such as gorillas is a good model for this. By conserving gorillas and their habitats and observing their way of life, we may be able to find a new way of life for the future. Such models need to be found in different parts of the world. .