In a study to determine sex differences in concerns over sexual versus emotional infidelity, researchers asked participants the following question:

Which upsets you more?
A) Imagining your partner having sexual intercourse with someone else?
B) Imagining your partner falling in love with someone else?

Roughly 60% of men selected sexual infidelity, A, as most upsetting, while 85% of women selected emotional infidelity, B.

Initially observed in the US, researchers replicated these sex differences in Brazil, Chile, China, England, Ireland, Korea, Norway, Romania, Spain, and Sweden.
Brooke Seelza later led a large research team that corroborated these findings in the Himba of Nambia, the Mayanga of Nicaragua, the Hadza of Tanzania, the Karo Batak of Indonesia, the Shuar of Ecuador, the Yasawa of Fiji, and the Tsimane of Bolivia.