Are there twin puppies

But when he looked inside, he found two puppies with their umbilical cords connected to the same placenta, an indication that they might be twins. After the procedure, de Cramer called in canine reproductive specialists to confirm his hunch. The researchers took blood samples when the twins were two weeks old and tissue samples from the brothers and their five litter mates when they were six weeks old.

The results showed that the pups, named Cullen and Romulus, were genetically identical. Identical twins are rare in the animal kingdom. Hogenboom reports that when two fetuses attach to one placenta, one or both of them often do not receive enough oxygen, causing the animals to die. Humans are an exception, however, with a two percent twinning rate.

But the scientists suggest that twins may be rarer in nature than among human beings because two organisms living in a single placenta can lead to less nourishment for each individual. In the tough world of nature, that can result in young that are less hardy and prepared to face the wild. In people, that is less of an issue now, thanks to the benefits of society and intensive parental care.

In people, the natural rate of twins is roughly one in 80 births , with identical twins making up roughly a third of that. The rate of identical twins has tended to be relatively consistent across nations and cultures, although it may tend to run in some families. The rate of fraternal or dizygotic twins tends to rise with the use of certain fertility assistance drugs. Identical twins develop after a single zygote, or fertilized egg, divides, creating two or more embryos.

Fraternal twins develop from two or more fertilized eggs. In people, identical twins do tend to form closer relationships than fraternal twins or other siblings, psychologist and twin expert Nancy L. Segal previously told National Geographic.

Identical twins often do seem to share some similar habits and quirks, but there are many differences that develop as well, thanks to different environmental impacts and possibly other unknown factors.

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