When pursued by a predator, she can jettison the bigger joey from her pouch, lightening her load and allowing her to escape. Unable to keep up with its mother, a teenage joey will perish without milk or protection from its mum. While this may sound heart-breaking to a human, for the kangaroo no painful conscious decision-making is required: natural selection has already furnished her with a functioning plan B.The cessation of suckling will trigger her embryo-in-waiting to emerge from developmental dormancy and serve as a rapid replacement for the lost joey.
