"Researchers long viewed infanticide and similar acts of maternal skulduggery as pathological, a result of the mother's being under extreme stress..."

".... it made little genetic sense for a mother to destroy her young, and maternal nurturing was assumed to be a hard-wired affair. More recently, scientists have accrued abundant evidence that 'bad' mothering is common in nature and that it is often a centerpiece of the reproductive game plan... [P]andas, for example, often practice  'a postnatal form of family planning, giving birth to what may be thought of as an heir and a spare, and then, when the heir fares well, walking away from the spare with nary a fare-thee-well.'"

From a CSM article titled "Baby elephant cries for 5 hours. Is Mom rejection unusual?"