We had picked up a male ASF to tempt a female ball who went off her feed, and found her in shed, so put the male in our rat rack. I've heard a lot about how bitey and unpredictable these little wild guys are, so I had some trepidation over it...but he was quiet, calm, and very docile. He simply went limp when you picked him up by the tail, and he retreated without darting around too much when you went after him.

A few weeks later, we decided to just go ahead and get a female asf, and raise a few of them.
The day we put her into the cage with him, she bit up his ears a bit, and then they settled down...however...

Now, when you open the bin, the male comes forward, and the female retreats. He is most definitely displaying guarding behavior, and has become much more aggressive. So it seems that aggression in ASFs may be the result of guarding when they are kept in groups.

Just a theory.