Female swamp wallabies are the only mammals that are always pregnant, Australian researchers write in the scientific journal PNAS. The swamp wallabies carry an embryo in one of their two wombs at all times.
Kangaroos and wallabies have two wombs. At the end of a pregnancy in one uterus, an embryo forms in the other uterus. This embryo can remain ‘unused’ in the body for up to eleven months. While the mother is still pregnant in one womb, she can become pregnant again and mate to reproduce through the other womb.
The ‘unused’ embryo starts to develop again as soon as the young born baby stops drinking milk from the mother. The embryo grows, the mother becomes pregnant again and a few days before the end of the pregnancy the mother forms a new embryo. Then the process starts all over again.
Most mammals need a break in between pregnancies, for example to suckle the born young, but swamp wallabies can immediately resume reproduction.
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