Men most typically experience a type of jealousy which described as sexual jealousy. They are most distressed when they imagine their partner involved sexually with another man. A study conducted by Miller and Maner in 2008 revealed that men become more distraught over imagining their partner involved in new sex positions, passionate sex or different sexual positions than falling in love with someone else. The effect size for the types of infidelity men choose was vastly different. Emotional jealousy (r2 = .12)was approximately half the size of the effect among individuals who chose sexual jealousy (r2 = .25) (Miller & Maner, 2008).
When it comes to sex, men have an added benefit. They are able to produce millions of sperm in a short period of time, which is advantageous in the reproductive realm. However, that is where their leverage ends. While women are always 100% certain that the baby they are carrying is in fact theirs, a man can never be sure. This paternal uncertainty is thought to be where male jealousy is derived from. A man who spends time and money on a child which is not his own will lose valuable resources. This is thought to be the source of this sexual jealousy (Buss, 2000).
As the video above shows, not even the mother can ever be 100% sure of paternity, even after 11 DNA tests.
(2006, November 20). 11th paternity test failed. [video file] video posted to https://www.youtube.com/watch?v=Mzktpj1PQHI&feature=related