They must have the same kind of reproduction as this: Adactylidium is a type of mite which probably has the fastest (and possibly the most disturbing) mating cycle of any animal: the male mates with his sisters in the mother's womb. The baby mites then eat their way out of the mother and the process is repeated in four days. In some species, the male emerges from the mother alongside his sisters and then dies a few hours later, while in other species, he doesn't emerge at all, because his only purpose was to impregnate his unborn sisters
Well, that also explains the lack of male Kangaskhan...
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I often wonder if we are growing as a people... or in fact, regressing.