Although psychological factors such as stress, anxiety, guilt, depression and the fear of sexual failure are considered to be the cause of male impotence in approximately 10% to 20% of cases , men also experience these same symptoms when the cause is believed to be physical, resulting in difficulty determining which is primary, the physical or the psychological problems.
This open the door for considering many physical symptoms not as direct causes of impotence but as psychological stressors that trigger the impotence. Here I propose that the male temporal impotence is an instinctive psicho-psychological mecanism that was designed by natural selection for controlling the couple reproduction for its own benefit when for some internal (phisycal) or external (social) problems put men in a state of weakness.
Contrary to many species of mammals, like many species of birds that give birth to defenseless offspring, the human male collaborate with the female in the upbringing of the offspring. Like these birds and like all the species with biparental care and internal fertilization, the male must control the behavior of the couple in order to assure that she does not copulate with other males, because, otherwise, the male is in a high risk of parenting other male´s Childs. (The Adapted Mind: Evolutionary Psychology and the Generation of Culture index pag. 290). Males that care for his paternity have more biological children that carry on their genes that indeed codify the female vigilance behavior so this vigilance behavior is evolutionarily stable.
When the male is too weak due to physical or social problems that compromise his position or it preview a weak position in the future, he becomes or will become less valuable for the couple. The couple can improve his reproductive outcome by copulating with other stronger males, and this is more probable because the male cannot carry out well his surveillance due to his weak position. At the same time, in this position, the male cannot support additional children, even its own. One possible strategy is to cease to copulate with his woman. With this behavior he assures itself that any pregnancy of the woman will not be of its own. This is a way of passive surveillance.
The woman however, is put in a reproductive bottleneck. His reaction is a feeling of frustration, proximately caused by the lack of sexual activity of his couple, but ultimately caused by the reproductive bottleneck that the man impose, that must have been an evolutionary pressure in the past. She can opt to help him, that is the best for the male, or, else, she can abandon it. This is a bad scenario, but even this is better that the worst scenario in evolutionary terms: to raise children not of his own. Agression and sequestration could be an alternative strategy for female retention, but this demand time and effort. Impotence is more convenient in case of a weak position: lack of time, lack of physical strength and so on.
Althoug nowadays the psichological stress can be triggered in non critical situations, in the past the psychological weakness were caused by real internal or external dangers. So the evolutionary pressure has been consistent during the past for the development of this strategy of passive reproductive control of the couple.
What predict this hypothesis is that males will feel the impotence with his couple rather than with other women, although, in general, the libido will be reduced. It is also expected that single stressed males may reduce its libido when fighting with transient problems.