Mammals in general provide parental care for their young. Thisseems to imply that parents should be able to recognize their ownyoung. Yet, for some mammals such as the wild mouse (Mus musculus),pup recognition by dams (mothers) does not occur (sires are notinvolved in parental care in mice). Dams will care for any pup thatis available. In the lab, if a dam is placed in a cage with two ormore litters of pups, she will gather them into one giant pile ofpups and attempt to nurse, groom and care for all of them. Anentire genetic litter can also be replaced by a new litter ofentirely unrelated pups and the dam will adopt and care for them asif they were her own. In meadow voles (Microtus pennsylvanicus),another common prairie rodent, pup recognition apparently does notoccur until 7-9 days have passed. Prior to that time, dams willadopt any young that appear in their nest. Under what evolutionaryconditions might non-recognition of offspring develop? Under whatevolutionary conditions should recognition of young develop?