The current Addo elephant population has grown from a very small gene pool of only 11 elephants. Of the original 11 elephants, there were some which did not have tusks (tusklessness does naturally occur in elephant populations) and many of the big tuskers were shot by hunters in the previous century. Tusklessness is one of the results of the small genetic pool but it does not seem to have affected / disadvantaged the elephants in any way. All bull elephants have tusks while currently only 13 cow elephants have tusks (some have only one tusk).
In 2002 and 2003, eight Kruger bulls were brought into the Park to diversify the gene pool, not specifically for tusks but to increase the health of the gene pool. In 2005, eleven of the more dominant Addo bulls were relocated to various private game reserves to give the Kruger bulls a better chance of breeding with the Addo elephant cows and therefore better chance of getting there genes into the population.
The Addo elephants were habituated to vehicles by Dr Anthony Hall-Martin (as Friedrich mentioned below) and over the years have become very used to vehicles - but NOT people out of vehicles
- at close quarters due to the number of vehicles they see daily in a relatively small area (compared to e.g. Kruger).
Musth bulls can be aggressive or irritable at times but it really depends on the specific bull and the period of their musth so its best to be cautious around them anyway.