Bringing a baby into the world is difficult, especially for parents. But what happens when they are twins, triplets, or even quadruplets? According to data from the Centers for Disease Control and Prevention in the United States, one in thirty parents has twins, and almost one in ten thousand must juggle to take care of their triplets. This, which is something quite unusual in humans, happens more frequently in other mammals.
In fact, in many animals having multiple pregnancies is the norm rather than the exception. For example, dogs have an average of five puppies per litter, as recorded in a study published in the journal Theriogenology . Thus, the difference between a litter and twin brothers really comes down to number, since a pair of twins refers to two babies, whereas animals that have a litter usually have more offspring.
A female has a litter when she releases several eggs and they end up being fertilized. These fertilized eggs later develop into multiple embryos. Instead, when a woman releases two eggs, we call the resulting babies identical twins or non-identical twins (that is, twins if they do not share the same placenta). The same happens when they are triplets, quadruplets or quintuplets.
What about identical twins?
Genetically identical siblings are formed when a single fertilized egg splits in two. This is very rare in humans, as approximately four out of every 1,000 births result in identical twins, according to the United States National Library of Medicine.
On the other hand, scientists consider that these pregnancies are less frequent in animals. In fact, vets have only identified identical pups once. In this rare case, which took place in 2016, a veterinarian performing a caesarean section on a female dog noticed that two of the puppies shared the same placenta. A genetic test confirmed that the puppies shared all of their DNA, making them identical twins.
However, there is still not much research on identical twins in animals, which is why they seem so rare.
The armadillo, a unique animal
Did you know that armadillos always give birth to identical quadruplets? Or, put another way, females release an egg that later divides into four after fertilization. Scientists don’t know exactly why this happens, although they have a theory: having identical quadruplets prevents inbreeding. Thus, siblings cannot mate with each other, so they must come out of their burrows to find a mate.
