Armadillos Almost Always Give Birth to Identical Quadruplets

The reproductive strategy of the nine-banded armadillo is exceptionally rare among mammals. The creature experiences a phenomenon known as obligate polyembryony, where a single fertilized egg consistently divides to produce multiple, genetically identical offspring. Shortly after conception, the single zygote splits into two, and then each of those halves splits again. This process results in four identical embryos that all share a single placenta, leading to the birth of a litter of natural clones, all of the same sex.

This predictable production of identical quadruplets has made the nine-banded armadillo an unexpectedly valuable subject in scientific and medical research. They have been particularly crucial in the study of leprosy (Hansen's disease). Armadillos are one of the only other animals besides humans known to naturally contract the disease, partly due to their lower-than-average body temperature, which the leprosy-causing bacterium prefers. Because the quadruplets are perfect genetic copies, scientists have a naturally occurring control group, allowing them to test treatments and study disease progression across four identical subjects while eliminating genetic variability as a factor in their results.