[tremon]

For me, the more important question is not whether all test subjects were genetically diverse: it's more important that the free rat and the caged rat are dissimilar. The situation would be vastly different if the rat pairs were related, since there is a genetically selfish motivation for caring for those within the same gene pool.

[jonlucc]

This becomes apparent when you try to co-house rats and mice. Litter mates are much less likely to fight.