There is an excellent chance that you know someone who has a twin sibling. In fact, there are some of you listening who have a twin brother or sister.
Multiple births are something that isn’t common but also isn’t super rare, either. However, multiple births have actually become more common over time despite the fact that there are some types of multiple births that are exceedingly rare.
Learn more about multiple births, twins, triplets, and more, and how they happen, on this episode of Everything Everywhere Daily.
Compared to most species, human births are an inherently dangerous thing.
Historically, childbirth has been one of the highest causes of death for women. This has to do with the fact that humans have evolved to have large brains, which has resulted in large heads.
About one birth in a thousand has a child with a head too large to fit through the birth canal.
Once a human child is born, they are totally helpless. If you’ve ever seen a video of a cattle or bison giving birth, the calf is often up and walking an hour or two after being born.
Human children won’t usually start walking until a year after they are born. Once they start walking, it will still be another year or two before they can reasonably function without the help of someone else.
Technically speaking, humans are born before they are done gestating. The reason they are born so early is that if gestation took any longer, their heads would be so large that birth would be impossible.
On top of all that, historically, it was very common for children to die before they reached the age of five. Infant mortality was the big reason why early human life expectancies were so low. Assuming you could make it past infancy, you had a good chance of living a long life.
I bring all of this up to illustrate the point that birthing and raising humans is actually very difficult. It is more difficult than it is for any other species that we know of.
Because it is so difficult, the default for humans is to give birth to only one child at a time. If you have more than one child, the risks of childbirth go up, the risks to the children go up, and the difficulty breastfeeding and raising the children goes up as well.
That being said, multiple births do obviously do occur. With modern medicine, most multiple births are no more dangerous than single births, both to the mother and the children.
So, as we get into this subject of multiple births, we should start with the most common form of multiple birth, by a wide margin, twins.
Twins are uncommon but not particularly rare. As I mentioned in the introduction, most of us probably know or are related to someone with a twin.
The percentage of births that result in twins varies around the world and has varied over time. The lowest rate of twin births can be found in South America and Southeast Asia, where 6 to 9 twins are born for every 1000 live births.
The highest rates of twins are found amongst the Yoruba people of West Africa, where 45 to 50 births out of 1000 result in twins.
The percentage of twins born over time has changed as well. In the United States, the number of births that resulted in twins was 9.4 per thousand in 1980. By 2009, it had risen 76% to 16.7 sets of twins born per 1000 births.
Recent data from the Centers for Disease Control in the United States reported the rate of twins to be 3.4% of births. This is actually a dramatic increase, a more than doubling of the number of twin births in just forty years.
This increase is almost exclusively due to the use of fertility drugs. The reason why these result in increased multiple births and why the Yoruba have so many twins, I’ll get to in a bit.
You are probably also aware that there are different types of twins.
The most common type of twins are fraternal or dizygotic twins.
Fraternal twins result from two eggs, each of which is fertilized independently of each other.
Each egg and each sperm is a unique mix of genes, which is why siblings can often look very different from each other.
Because separate eggs are fertilized by separate sperm, you can have twins that don’t look the same or are even different sexes.
Fraternal twins will develop in separate amniotic sacs as a result.
Statistically, women from families with high rates of fraternal twins are more likely to have fraternal twins themselves.
Normally, eggs resulting in fraternal twins will be fertilized at almost the same time. There is a rare condition known as superfecundation, where eggs can be fertilized by sperm from different men.
In Greek mythology, the twins Castor and Pollux actually had two different fathers. Castor was the son of Tyndareus, and Pollux was the son of Zeus.
In such cases, the children are actually genetically half-siblings despite being twins.
The other type of twins you are probably familiar with are identical twins or monozygotic twins.
Identical twins are produced in a totally different way. It results when a single fertilized egg forms a zygote, which splits to form two separate embryos.
The percentage of identical twins to fraternal twins will vary depending on where in the world you are. Fraternal twins are twice as common in regions with low numbers of twins as eight to ten times as common in rates with high numbers of twins.
The rate of identical twins is approximately three sets of identical twins per one thousand births.
Variance in the number of twins born across time and place is almost exclusively due to increases in the number of fraternal twins, not identical twins.
Because identical twins come from the same fertilized egg, they have the same genetics. That is why they look the same and are always the same sex.
There is another type of twins, which is extremely rare. It is so rare that there have only been two recorded examples of it, although there have almost certainly been more, but people just didn’t know it at the time.
They are known as Sesquizygotic twins.
Sesquizygotic twins have similarities to both fraternal and identical twins, but it requires multiple rare events to take place. It occurs when a single egg is fertilized by two different sperm. Normally, when this happens, it results in three sets of chromosomes, and the fertilized egg will not survive. This is rare event number one.
However, in rare cases, the fertilized egg can sort itself into three different cells. If the two sperm cells carry different sex chromosomes, one with X and one with Y, then you can wind up with cells that have an XY coming from mother and father, an XX cell with chromosomes from mother and father, and an XY cell with both chromosomes coming from the father.
The latter cell, with both sex chromosomes coming from the father, can’t develop, but the other two cells can exist in the same ball of cells. This is rare event number two.
Finally, the ball of cells with both XX and XY cells would split, creating two different embryos. This is rare event number three.
The result is a set of twins, one male, and one female, similar to fraternal twins. However, they share the same amniotic sac, like identical twins.
Sesquizygotic twins are also known as half-identical twins. They share more genetic material than fraternal twins but not as much as identical twins.
There have only been two cases ever reported, one in the United States and one in Australia. However, if there were other cases, most people probably wouldn’t know it as it would appear as a normal twin birth.
Once you get beyond twins, then things do become quite rare.
While most of us know someone who is a twin, most of us probably don’t personally know someone who is a triplet.
That is because triples are much more rare. Triples can be identical, fraternal, or a combination of them.
Most commonly, they are the result of three separate fertilized eggs. However, it could happen when two eggs are fertilized, and one of them identically splits, and in the rare case, one single egg can split into two, and then one of those two eggs can split again, resulting in identical triplets.
Triplets generally only occur in about one in every thousand births. Identical triplets occur only about once in every million births. Identical triplets are so rare that if a set of them are ever born, it will usually make local news.
In 2015, there were only four sets of identical triplets born in the entire United States.
Beyond triplets, multiple births become extremely rare. There are only 3,556 known sets of quadruplets in the world, of which only 70 are identical quadruplets.
The process of making quadruplets is the same as with triplets, with some combination of multiple eggs or zygotes splitting.
This many children being able to survive birth at the same time is an almost totally modern phenomenon. In ancient times, either the children and/or the mother wouldn’t have survived.
The first recorded case of quadruplets that survived into adulthood was the Fisk quadruplets, born in 1783 in Connecticut.
Once you get beyond quadruplets, the odds of it happening and the odds of all the children surviving are so low that anyone who has them will probably wind up with a reality TV show.
Quintuplets, five children, are believed to occur naturally once in every 55,000,000 births. The first surviving set of quintuplets in history were the Dionne quintuplets in Canada, who were born in 1934 and on whom I’ve done a previous episode.
The world’s first case of sextuplets, six children, that were born alive was the Thorns sextuplets born in Birmingham, England, in 1968. Three of the children died within two weeks of birth.
The Rosenkowitz sextuplets, born in 1974 in Cape Town, South Africa, were the first sextuplets to survive into adulthood.
The first surviving set of septuplets, seven children, were the McCaughey septuplets born in Iowa in 1997.
The first ever recorded birth of octuplets occurred in 1968 in Mexico City, but all eight children died within hours of birth.
There have been, ironically, eight recorded instances of octuples in history. In every case but one, at least one, if not all, of the children died soon after birth.
The only case of surviving octuples were the Suleman octuplets born in 2009 in California.
There have only been three cases of nonuplets, nine children, born in history. In two cases, all of the children died. In the most recent case, which was born to a couple from Mali while they were in Morocco in 2021, all nine children have so far survived and are healthy.
What is responsible for such extreme multiple births?
The first and overwhelming reason for the rise in the number of twins over the last several decades, and other extreme multiple births, is the use of fertility drugs.
Fertility drugs result in the release of multiple eggs which can be fertilized. Normally, it simply increases the odds that one of them might become fertilized and take hold. However, it also increases the possibility that all of them might become fertilized, hence, while still rare, you see more of the extreme multiple births over time and more twins.
In the case of the Yoruba people, it is widely thought that the reason for the high number of twins might have to do with a particular type of yam consumed in the region, which constrains a natural phytoestrogen that stimulates the release of multiple eggs.
Another reason why more children from multiple births are able to survive is due to the improved care of babies born prematurely. Almost all multiple births run the risk of premature birth, and in the case of extreme multiple births, it almost always happens. It is almost impossible to have a full gestation period for that many children.
That is why almost all of the cases of surviving extreme multiple births have taken place in just the last few decades.
Also, extreme multiple births almost always are delivered via caesarian section, which was a procedure that, until relatively recently, was only performed in extreme cases and often resulted in death. Today it is a regularly done procedure at most hospitals.
On top of that, developments in infant formula have made it possible for infants from extreme multiple births to survive, whereas in the past, they might have starved to death.
Multiple births have always been a part of humanity, but recent developments in fertility treatment and medicine have made multiple births more common and have dramatically improved survival rates, which means there are more twins, triplets, quadruplets, and quintuplets than ever before.
The Executive Producer of Everything Everywhere Daily is Charles Daniel.
The associate producers are Thor Thomsen and Peter Bennett.
Today’s review comes from listener Abdullah over on PodcastAddict. They write:
Abdullah here to inaugurate the Pakistan chapter of the Completionists’ Club. Don’t think I’ve ever been more engrossed by any form of media (maybe reading LOTR the first time around).
GREAT Podcast, from the unpredictability of topics to perfect delivery. Never change.
However, would love to see more topics from my Native land (which has been tangentially mentioned many times)
Will have a piping hot celebratory Briyani.
Thanks, Abdullah! First, let me congratulate you because, as far as I know, you are the first member of the Pakistani Completionist Club. The first of your 241 million countrymen to have completed the fete.
Also, I do have some Pakistan-related episodes on the list, including more on the Indus Valley Civilization, one of the foundational civilizations in the world, and an episode on the partition of India and Pakistan, which was one of the most significant events in the post-war 20th century.
Remember, if you leave a review or send me a boostagram, you too can have it read on the show.