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Nine-banded armadillos are unusual enough in appearance, but their reproduction is even more curious. A litter of these animals always consists of four same-sex, genetically identical siblings. A single fertilized embryo splits into four that all develop into armadillos. Apparently, the female armadillo's uterus has a very small implantation site, where only a single fertilized egg can implant. Although some species of armadillo can therefore only produce one offspring at a time, egg splitting allows the nine-banded armadillo to produce larger litters. The authors spotted a chance to study potential kin selection—essentially relatives working together to increase how many of their genes get passed to future generations. As they explain their results, the authors also explore much of the nine-banded armadillo's natural history.
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