Same-Sex Sexual Behavior Found in Macaques, Bonobos and Chimpanzees — Study

Scientists have identified widespread same-sex sexual behavior among several nonhuman primate species, including macaques, bonobos and chimpanzees, offering new insights into animal social systems and evolutionary biology.

The discovery comes from a large-scale scientific review published on January 12, 2026, in the journal Nature Ecology and Evolution. The study analyzed decades of observational research and concluded that same-sex sexual behavior is not unusual or accidental among primates but may serve important social and survival functions.

Researchers examined 96 peer-reviewed studies covering 491 nonhuman primate species. Out of these, 59 species were documented engaging in same-sex sexual behavior, with the practice observed frequently in at least 23 species. The behaviors ranged from mounting and genital contact to other non-reproductive sexual interactions.

According to the study, these activities were particularly common among macaques, bonobos and chimpanzees—species known for their complex social structures and long-term group living. Scientists believe the behaviors help strengthen social bonds, reduce tension, and manage conflict within groups.

Lead researcher Vincent Savolainen, an evolutionary biologist at Imperial College London, said the findings challenge outdated assumptions about animal sexuality. He explained that same-sex sexual behavior appears to be a normal and functional part of primate life rather than an evolutionary anomaly.

The study also found that environmental pressures play a significant role. Same-sex sexual behavior occurred more frequently among primates living in harsh conditions, such as dry habitats with limited food availability or high predation risks. Species with strict dominance hierarchies, longer lifespans, and clear physical differences between males and females were also more likely to exhibit the behavior.

Scientists suggest that in such environments, social cooperation and flexibility become critical for survival. Same-sex interactions may help animals maintain alliances, defuse aggression, and promote group stability.

Experts not involved in the research say the study is important because it examines animal behavior at scale. Isabelle Winder, an evolutionary anthropologist at Bangor University in the United Kingdom, described the work as groundbreaking, noting that it treats same-sex behavior as a meaningful biological phenomenon rather than a curiosity.

While the findings deepen understanding of animal evolution, the researchers caution against drawing direct conclusions about humans. Human behavior, they note, is influenced by complex social, cultural and historical factors that differ significantly from those shaping animal societies.

Still, the study adds to growing scientific evidence that same-sex behavior is widespread across the natural world and may offer evolutionary advantages. By reframing these behaviors as adaptive, researchers say the findings help broaden public understanding of biology, evolution and social intelligence in animals.