What is triggering elephant aggression?

If elephant numbers are down and food is plentiful, what is triggering elephant aggression? Have we been the agent for natural selection by culling the least aggressive elephants?

Or has some change in the environment led to a behavioral adaptation leading the elephants to become more territorial? Is that environmental change simply the introduction of humans and our territorial expansion or is it something else?

Or perhaps UV radiation signals a changing epoch and elephants respond by leveraging their dominance?

"Across Africa, elephants seem to be turning on their human neighbours in ever increasing numbers. Although such attacks are nothing new, they have always been seen as a side effect of elephants competing for food and land, either as a result of population explosions or because people have encroached on elephant territory. But that may not be the whole story.

'Elephant numbers have never been lower in Uganda. Food has never been so abundant,' ..."

Elephants on the edge fight back - life - 18 February 2006 - New Scientist: