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1Scan for outdated or missing drivers - takes under a minute2Repair Windows errors before they cause bigger problems3Fix the driver behind crashes, sound loss and screen glitchesSame-sex sexual behaviour has been reported in more than 1,500 animal species, but that is a count of species with published reports—not the percentage of animals that engage in it. Scientists do not have a reliable, standardized percentage for how many individual animals show the behaviour across all species. The evidence varies in how species are defined, observed and studied, and many animals have received little research attention.
What does “same-sex sexual behaviour” mean in animal research?
Researchers use “same-sex sexual behaviour” (SSB) to describe observed sexual activity between same-sex individuals. One 2023 mammal analysis defined it broadly as “any attempted sexual activity between members of the same sex.” That can include behaviours such as courtship or mounting; the definition refers to observed acts, not an animal’s identity or exclusive sexual preference. Gómez, González-Megías and Verdú, Nature Communications (2023).
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How many animal species have reports of it?
Published reports cover more than 1,500 animal species, according to the 2023 mammal study’s background review. The count answers “in which species has the behaviour been reported?” It does not say what share of individuals in those species show it, how often they do so, or whether any individual behaves exclusively toward same-sex partners. Source: Gómez et al. (2023).
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Other studies use narrower groups or different denominators. These figures describe distinct kinds of evidence and should not be added together or read as comparable prevalence rates:
#1 Best Overall
| Evidence | What was counted | What the figure means |
|---|---|---|
| Animal species overall | More than 1,500 species with published reports, as cited in a 2023 mammal analysis | A documented-species count, not a percentage of animals or frequency of behaviour. Gómez et al. (2023). |
| Non-human primates | 491 species assessed; behaviour documented in 59 | Species-level records in a comparative primate study, not a rate among individual primates. Coxshall et al. (2026). |
| Invertebrates | Approximately 207 species with published evidence | A systematic synthesis reported this approximate count and cautioned that research effort and study types shape the apparent distribution. Invertebrate synthesis (2026). |
| Mammal researchers | In an online survey, 77% of respondents said they had observed SSB, 48% had collected data, and 19% had published findings | Percentages of survey respondents—not percentages of mammals or mammal species. Anderson et al. (2024). |
Can scientists say what percentage of animals are gay?
No universal percentage is established. The studies summarized here do not provide a standardized cross-species estimate of the share of individual animals that engage in SSB. Producing one would require comparable observations across many species, including consistent definitions, sampling and measures of frequency. The available species tally does not supply those data.
“Gay” can also imply an identity or enduring pattern of exclusive preference. Reports of a particular act do not establish either. The evidence supports statements about observed behaviour in particular species or study populations, not a general estimate of animal identities or exclusive same-sex orientation. Gómez et al. (2023).
Rank #2
What did the 2026 primate study find?
Coxshall, Nesbit, Hodge and colleagues assessed 491 non-human primate species, documented SSB in 59, and tested relationships with 15 environmental, life-history and social traits. They reported greater occurrence in species associated with drier environments, food scarcity and predation pressure, as well as in species with greater size dimorphism, longer lifespans, and more complex social structures and hierarchies. Coxshall et al., Nature Ecology & Evolution (published January 12, 2026).
The authors’ structural equation model indicated that social complexity directly promoted occurrence in their analysis, while environmental and life-history traits mainly had indirect associations. These are comparative associations across primate species; they do not show that any one factor causes the behaviour in every species or explain the behaviour of every individual. The authors characterize SSB as context-dependent and shaped by interacting ecological, life-history and social factors.
Rank #3
Why don’t published records give a complete picture?
Species and individuals are different denominators
A species can have a published report even if researchers do not know how often the behaviour occurs or how many individuals show it. Conversely, the absence of a published report does not establish that the behaviour is absent in nature.
Research effort is uneven
The 2026 invertebrate synthesis found that published work was concentrated in insects and particular study types, and cautioned that research effort affects which groups appear in the literature. In mammals, an online expert survey found a gap between observation and publication: respondents were more likely to report observing SSB than collecting data or publishing findings. Neither result supplies a correction factor for estimating how much behaviour goes unrecorded. Invertebrate synthesis (2026); Anderson et al. (2024).
Rank #4
Methods and settings differ
Evidence may come from an anecdotal observation, systematic field observation, captive study, expert survey or comparative analysis. Those approaches answer different questions. When reading a claim, check which group was studied, whether observations were wild or captive, how SSB was defined, and whether the reported number measures species occurrence, individual frequency or publication history.
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Scan for outdated or missing drivers - takes under a minuteDriver Scan →Clear out junk files and repair common Windows errorsFree Scan →Fix the driver behind crashes, sound loss and screen glitchesFind Drivers →Does same-sex behaviour have one evolutionary explanation?
No single function or evolutionary explanation has been established across animal groups. Researchers have considered both adaptive and non-adaptive explanations, and a 2009 review called for theoretical, comparative and experimental approaches to clarify how SSB evolves and what effects it may have. Bailey and Zuk, “Same-sex sexual behavior and evolution,” Trends in Ecology & Evolution (2009).
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The primate findings add evidence about associations in one broad group; they do not settle the explanation for other primates, much less all animals. Behaviour observed in different species need not have the same causes or consequences.
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