Aggression

One evolutionary explanation of human aggression is the idea of infedility and jealousy. This was a major concern for our male ancestors as when they found a mate, they wanted to retain her to be able to pass on their genes. This brought males into direct competition and according to the psychologist Carrier this was the root of much of male aggressive behaviour. Therefore, male sexual jealousy is the fear of a threat to their sexual partner by another potentional sexual partner for the female. This is because it can lead to cuckoldry, when a woman deceives her partner into investing in her offspring conceived by another male. Cuckolded men lose out in resources and reproduction oppurtunities thus fear this situation. This fear then leads to mate retention tactics, such as violence to ensure they retain their female partner and make sure they are investing in their own genes and not another mans.This jealousy may have come from the supposed sexual infidelity of our female ancestors and so men fought to stop this happening. Therefore, sexual jealousy is an adaptive function that has been passed through our genes because of it's usefullness. 

Buss 1995

Argues that men and women differ in responses to infidelity in ways that have resulted from different adaption to different reproductive situtations. The evolutionary theory views infidelity as distubing to both sexes, but believes that the cues triggering sexual jealousy are weighted differently in males and females. Men are more distressed about sexual infidelity because of the problem of uncertain paternity and cuckoldry, a means of wasted resources. If a man is suspect to a woman's faithfulness, it evokes sexual jealoust and possible agression.

Buss and Shackelford

214 individuals and found men reported a significantly higher use of debasement and intra-sexual threats compared to women. Women reported a greater use of verbal possession and threats of punishing infeditily. 

Wilson et al

Found that amongst women who claimed their partners used guarding tactics, such as not allowing them to talk to other men, 72% of them ended up requring medical attention following an assault from their partner. 

(I) socially senstive, an excuse

(A) Biological - genes