[1]https://guardian.ng/life/the-namibian-tribe-where-sex-is-offered-to-guests/

[2]https://guardian.ng/life/the-namibian-tribe-where-sex-is-offered-to-guests/

[3]https://link.springer.com/chapter/10.1007/978-3-540-79116-4_5?noAccess=true

[4]https://www.uwlax.edu/globalassets/offices-services/urc/jur-online/pdf/2000/helmrick_and_reiser.pdf

[5]https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3731873/

[6]https://onlinelibrary.wiley.com/doi/full/10.1111/bcpt.12653

[7]https://www.nature.com/articles/3900719

[8]https://www.pnas.org/doi/10.1073/pnas.0308292101

[9]https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3551978/