The birth of twins is usually a reason for joy for most people, but this does not happen very often. On the other hand, in the animal world a birth that brings to life several cubs is something almost commonplace. However, even if we tend to refer to them as twins, things are not quite like that. In fact, the question is whether animals can actually give birth to twins.
What are baby twins in the animal world
For many species of animals, it is normal to give birth to several young at a single birth. Pigs, for example, can give birth to 11 piglets, even more at once. But are those chicks and twins, even if they have the same “birthday”?
First of all, we need to know what twins actually mean. They can be identical – or monozygotic – which is what happens when a single fertilized egg divides to give birth to two embryos.
Identical twins may share the same placenta, but each has its own amniotic sac. Genetically, they are identical, they will have the same sex, the same physical traits and characteristics.
On the other hand, there are also fraternal twins – or dizygotic twins – the most common type of twins, which occur when two different eggs are fertilized by two different sperm.
Each twin has its own placenta and amniotic sac. They can be the same sex, but they can also be different sexes, and genetically they are as similar as any other two siblings who are not necessarily twins.
In the US, for example, 3% of pregnant women give birth to twins. Most of them are fraternal, and about a third are identical.
Why we can fool ourselves, how often they actually meet
In the animal world, each species has its own standard for the number of young born at one birth. People tend to know more about domesticated species, which can be pets or farmed.
A study that looked at the size of more than 10,000 puppies of purebred dogs found that the average number of litters at a birth varies depending on the size of the breed, according to iflscience.com.
Small breeds – such as chihuahuas or “toy” poodles – which generally weigh less than 4.5 kilograms, give birth to an average of 3.5 puppies per litter.
On the other hand, large breeds – such as the Mastiff or the Great Dane – whose weight is over 45 kilograms – can give birth, on average, to more than 7 puppies in a single birth.
On the other hand, when it’s just two puppies, people tend to refer to them as twins. Twins are more common in goats, but also in sheep, although births of a single kid or lamb are the most common.
Horses, on the other hand, whose pregnancy lasts 11-12 months, and cows, whose pregnancy lasts 9-10 months, tend to have only one foal or calf. Farmers, but also veterinarians believed, for a long time, that it is more economically profitable to encourage the birth of twins in these animals.
But twins in horses and cattle can bring complications for them and the birth of poorly developed foals or calves, with increased risk of premature death, endangering even the life of the pregnant animal.
Therefore, animals can give birth to twins, but more complicated is the question of their nature: are they identical or fraternal?
Dogs and cats produce several eggs at a time. Fertilization of a single egg by different sperm produces multiple embryos. The result is fraternal, non-identical offspring, even when they appear to be very similar.
Biologists believe that the birth of identical twin chicks is very rare in the animal world. What can take us is their very similar appearance, which is why, to our eyes, they appear to be identical. But this can only be proven through DNA testing.