Summary

Female elephants and their offspring live in family units. Male elephants live alone or in bachelor herds. The family units have a large amount of kin selection. This social system of the family unit appears to be caused by two main factors. Firstly, the extended socialization periods of young elephants necessitates a family unit. The family unit provides help in alloparenting and group defense of the young (which is rarely needed). Secondly, environmental pressures contribute to the system of the family unit. The older elephants in a family unit, especially, the matriarch, contribute valuable experience with regards to foraging strategies. Elephants have home ranges, because the areas they utilize are too large to economically defend. Elephants have low predation pressures (except for humans).
The bulls do not live with the family unit for several reasons. Elephants have the mating system of hierarchical promiscuity. Females do not need any resources from a male in order to raise an offspring, because resources are too widespread to defend and the family unit provides help in raising the offspring. Thus, males do need to stay with a family group in order to provide resources. Since family units rarely have a female in estrous, it would not be to a bull's benefit to stay with one group. Rather, during the limited time period of musth males often travel widely, searching for females in estrous Furthermore, it appears that bulls have different foraging strategies than family units because of the different metabolic requirements resulting from sexual dimorphism (Stokke 1999).