A common question that occurs about nonidentical twins is that we see they mostly happen in every other generation. This raises the question of whether twins always skip a generation.
Well, to logically support or debunk that we need to define what type of twins we are talking about and then explain scientifically. As medical science developed we have tons of information in the palm of our hands. Let’s look at a few of them and learn the true answer.
Knowing the Background and Classification
When we first try to talk about a myth or a fact, we need to define the subject. The subject in question that we will talk about only matters to one specific type of twins. And we could easily skip to that. However, it also matters that we explain why other types of twins are not a part of this question. In order to know that, we need to learn about how twins are born.
There are different types of twins with specific genetic reasons to be a particular type. We usually think twins are identical. Identical twins are formed from a single egg fertilized by a single sperm. It is therefore called monozygotic twins. The rate of which is very low about 0.03%.
This separation can happen at any stage of embryonic development, usually within the first two weeks after the egg gets fertilized. Monozygotic twins are born identical and have the same DNA. It also happens coincidentally as a single egg can be separated. Some reports suggest that genes play a role here but the information isn’t established. While monozygotic twins share the same DNA, they do not have identical characteristics.
This is because genes can also be influenced by various factors such as environmental factors and epigenetic modifications. This phenomenon is quite interesting. BBC has visual content to learn some interesting facts about identical twins. You can watch that here
On the other hand, fraternal twins who are not identical have been found to have some reasons. It happens when two eggs are fertilized at the same time. Hence, nonidentical twinning occurs. This type is more common than identical ones. And so far, we know that it doesn’t happen randomly. Fraternal twins can run in families, and the likelihood of having fraternal twins is influenced by maternal factors, such as age, family history, and fertility treatments.
Fraternal twins are more common in older mothers, in women who have a family history of fraternal twins, and in women who use fertility treatments to conceive. Fraternal twins share physical similarities but can also look very different from each other. They may have different hair and eye colors, different facial features, and different heights. They also have different blood types, just like any other siblings.
But they may also develop certain medical conditions that run in families or are influenced by environmental factors. For example, if one twin develops a medical condition, the other twin may have a higher chance of developing the same condition due to shared genetic and environmental factors.
There are also some other types of twins such as:
Half-identical twins are a rare type of twins that occur when an egg is fertilized by two sperm. As a result, there are three sets of chromosomes instead of the usual two. This creates an embryo with a mix of genes from both parents, making the twins half-identical.
Another type is conjoined twins. We usually see them in the media or the news where two twins are joined physically. They are connected to each other at some point in the body. It happens when the egg doesn’t separate fully into two embryos. The third one is mirror image twins where the twins have exactly reversed images of each other.
The Reason Behind Fraternal Twins
Before we debunk or accept the statement it is important to know whether fraternal twins are genetic or not. According to an article published by Newyork Times, fraternal twins are genetic. They happen because of the hyperovulation that runs in the family. Now what is hyperovulation? It is when the uterus releases more than one egg during ovulation.
This occurrence can happen because of genes. If women in the family are known to have hyperovulation chances are it will happen in every female body. However, hyperovulation can happen to people who don’t have it in the family. So it is not purely coincidental but there is a genetic option. Which gene influences it is yet to be discovered by science. But according to reports, women who are fraternal twins have a 1/60 chance of having twins meaning 1 in 60 women will have fraternal twins if they themselves are one.
In the case of male family members or twins, the number is 1/125. It means that one out of every 125 fraternal twin men has a chance of having another fraternal twin kid.
Do Twins Always Skip A Generation
Now comes the question of whether twins really skip a generation. Since fraternal twins are genetic, genes have a role to play. Those who have hyperovulation in the family are more likely to have fraternal twins. But the belief that they always skip a generation isn’t true.
In other words, that belief doesn’t have any scientific reason to happen. That belief comes from the assumption of twinning is a genetic reason. While that’s partially true because of hyperovulation, it mostly depends on chances.
It is also proved in medical science that this belief has no concrete science to support it. According to a study published in the journal Human Reproduction Update, the occurrence of twins is primarily determined by maternal factors, such as age, ethnicity, and family history, as well as environmental factors, such as fertility treatments and nutrition.
The study found no evidence to suggest that twinning skips a generation, and concluded that “there is no clear evidence of genetic factors specifically influencing the likelihood of dizygotic twinning” (Lambalk et al., 2011).
However, the generation gap might have another explanation. Since the hyperovulation trait passes on through genes it can only appear in girls. So if someone with that trait has a son, the son can’t demonstrate it. He can only carry the gene to the next generation. Hence, the women in the second generation get hyperovulation.
However, this is only a hypothesis without any logical facts or sources to back it. It can also mean that the genes might not show it for generations. The reason might be not having female carriers or not carrying that specific DNA. Even with this explanation, it is clear that if it happens, it will only be true for fraternal twins since they are born through hyperovulation. For identical twins, none of the explanations or hypotheses really work.
Other Facts Contributing to Twinning
While it isn’t certain what exactly contributes to twins, there are some factors that increase the likelihood of it. But it is very important to remember that even with all these things the rate of twins is pretty low. Some of the factors are mentioned below:
We often see information that maternal age also influences the chance of having a twin. It is true but not greatly. There are several reasons why it might happen. Older women are more likely to get artificial fertility treatment which increases the chance of having twins.
Also, they might have other risk factors. Like the previous history of multiple babies, medical conditions, etc.
Weight and Height
Body structure or anatomy matters a lot during pregnancy. It can influence so many things and the likelihood of having twins is one of them. Women who are taller and bulkier are more likely to have twin babies. They also have more capacity to hold multiple babies without having too much complicacy. They also consume more amount of nutrients than smaller women. Therefore their bodies are more capable of having twins.
This factor can be backed with data. Statistically, we see women of a certain race had more twins than others. Data tells us that black and white women who aren’t Hispanic have the most amount of twins. We also learn that those with Japanese ancestry have the least number of twins. Although the reason is unknown and so we can’t give a valid reason. But we can assume it has something to do with DNA. It could also mean these women produce multiple eggs more than others.
Twin Pregnancy Experience
Women who had twins before are more likely to have twins again. It only adds to the points we already explained that those who release multiple eggs might release again. Women who had fraternal twins already released multiple eggs before. So we can assume that their bodies are capable of producing and carrying multiple babies again. If you are a mother of twins who is reading this, double congrats to you!
Folic Acid Supplements
It is well-known to those who are trying to get pregnant that having folic acid might increase your chances. It is also considered to be a factor in twin pregnancy. But in both cases, this phenomenon has been suggested in small studies with a small sample. There is no authentic source with larger samples to make this a theory.
However, those who are trying for babies can take folic acid to increase the chances if it’s possible. Folic acid is normally essential for the human body, especially for women. Because they lose blood, it can boost nutrients. Moreover, it can help the baby’s development too. So, those who are trying to look for twin pregnancy factors can take folic acid regardless.
This is an important factor that many consider contributing to twin pregnancy. If we look at data, in the USA naturally 1 out of every 250 pregnancies are twin pregnancies according to the American Society for Reproductive Medicine. But some women get fertility treatment to have a higher chance of getting pregnant.
These treatments aren’t natural so they stimulate the hormones responsible for releasing eggs a bit more. As a result, women often release multiple eggs. We know when multiple eggs are released they get fertilized and twin pregnancy occurs. The same thing happens here. It is so frequent that the American Society for Reproductive Medicine estimates 1 in 3 women who get fertility treatment will have twins.
We can reach an intuitive explanation here that women who get fertility treatment are more likely than not to have multiple eggs fertilized and therefore get twins. Also, a specific type of fertility treatment known as In Vitro fertilization(IVF) implants embryos in women, While they implant multiple ones to increase the likelihood of pregnancy, women can get pregnant with many. So this type of treatment can also be responsible for twin pregnancy.
How twins are born and why are still some of the unanswered questions of science. Questions like this are appreciated because they give researchers a topic to enquire about.
Mostly the why behind twinning is still unknown and is something that needs much more research to decide. However, it is quite evident that twins don’t always skip a generation.