Cases of identical twins in nature are believed to be very rare because two organisms sharing placenta means less nourishment for both, which in turn means that the twins are not as strong as their other siblings and underprepared for the harsh life that nature has in store.
This is why the recent birth of two Irish wolfhound puppies has scientists excited - the puppies have been confirmed through genetic analysis to be identical twins.
It has been suspected for years that identical (monozygotic) twins are possible in domestic dogs, and there have been anecdotal reports, but there has never been a confirmed case until now.
Cullen and Romulus, the identical twin puppies in question, were delivered by vet Kurt de Cramer in South Africa as a cesarean section was needed for the mother, who was in distress. He found that the two puppies were attached via umbilical cords to the same placenta, which was something that he had never seen before in decades of practicing veterinary medicine.
Cullen and Romulus have five other siblings, none of whom were identical twins, so were each surrounded by their own placenta as is usual in dogs. Kurt de Cramer realised that the two puppies looked strikingly similar despite the slight differences in white markings.
De Cramer invited several scientists to test the pups and they could confirm that the twins were identical, being born from the splitting of a single fertilized egg rather than two distinct zygotes. The team published their findings in the journal Reproduction in Domestic Animals last week.
The differences in colours can be explained by the fact that genes are influenced by environmental factors, which is why even human identical twins can sometimes be distinguished from each other.
Source: National Geographic