Gerbils should never be kept alone. They have a very strong sense of social behavior and need a partner with whom they can play and cuddle. Thus, it is not always young, one should opt for same-sex animals.
Unfortunately, they also have a strong territorial behavior. The result is that foreign animals are marketed with a lot Agrressivität / killed. One must keep gerbils never with other animals (eg mice color) together!
The group recognized by the group odor. Anything that smells like her own is attacked. Therefore one should touch the animals only if the hands do not smell after fragrances. So wash your hands without soap. Not doing so can the animal that you have touched, smelled of strong fragrances different and attacked.
This is one reason why non should be too large for more than two animals, the cage size. It provokes other disputes. That does not mean that you should pen in the animals, just so they do not argue.