If there is an extraterrestrial college student orbiting Earth or floating invisibly among us while writing a thesis on human behavior, then current events have provided some good examples of one basic human trait: retaliation.
Retaliation was, for example, implicit in President George W. Bush as justification for the invasion of Iraq. And in Japan, the elementary school killer of her 12-year-old classmate Satomi Mitarai told police that her victim had said she was "heavy" and a "goody-goody." On June 1, the 11-year-old stabbed Satomi in the neck with a box cutter.
If our ET college student made a detailed study, she/he/it would notice that retaliation occurs among nonhumans too. In birds (blue-footed boobies and European moorhens), elephant seals, side-striped jackals as well as in a host of primates, animals will use violence in response to violence. Animals will attack another animal that has injured them.