For the first time scientists have discovered two animals of completely different species having sex.
Researchers have published on the sex in Japan, between a male Japanese macaque and female sika deer.
Sex between animals of different sorts has previously been recorded, however these instances have been between those that are closely related and look similar, according to The Independent.
Such cases have also typically been seen as a form of sexual harassment, such as king penguins being harassed by Antarctic fur seals.
In the paper, entitled Interspecies sexual behaviour between a male Japanese macaque and female sika deer, the scientists say it appears that the act between the monkey and deer was consensual.
Japanese macaques have been known to ride along on deer, but researchers say the monkey in the study “showed clear sexual behaviour towards several female deer."
Whilst some deer tried to escape, others appeared to be accepting.
Scientists are not sure why this has happened, but they believe the reason could be mate depravation. Another reason could be that the two species already co-operate, encouraging the monkey to make sexual contact.
Scientists hope to further study instances of sex between different species and also hope to learn more about why humans sometimes show sexual interest in animals.