The 244 individual twins' IQ's are normally distributed, with the mean = 96.82, SD = 14.16. The mean absolute difference between twins is 6.60 (SD = 5.20), the largest difference being 24 IQ points. The frequency of large twin differences is no more than would be expected from the normal probability curve.
Using the family-based adult sample, no differences in IQ scores were found between twins and their singleton siblings.
Many scientific studies have looked at IQ between identical twins, and for the most part, identical twins have similar IQs. There can be some developmental differences due to environment during childhood, but adult identical twins typically have similar IQs.
Monoamniotic-monochorionic Twins
This is the rarest type of twin, and it means a riskier pregnancy as the babies can get tangled in their own umbilical cords. If you have monoamniotic-monochorionic twins, your healthcare provider will monitor your pregnancy closely.
Having identical twins is not genetic. On the other hand, fraternal twins can run in families. Genetics can definitely play a role in having fraternal twins. For example, a woman that has a sibling that is a fraternal twin is 2.5 times more likely to have twins than average!
So, I will give them the benefit of the doubt. You probably already know the difference between identical and fraternal twins. Identical twins have 100% of their DNA the same while fraternal twins share only 50%.
According to The American Society for Reproductive Medicine, women who are fraternal twins have a 1 in 60 chance of having twins, and men who are fraternal twins have a 1 in 125 chance of fathering twins. It was previously believed that identical (monozygotic) twins were random — not genetic.
As expected, first-born twins had greater birth weight than second-born twins. With respect to height, first-born twins were slightly taller than second-born twins in childhood.
Once the babies are large enough to stay in one position in the womb, the twin lowest in the uterus is known as Baby A and the one furthest from there is Baby B, according to the Stanford Medicine News Center. In the majority of vaginal births, Baby A is born first.
Twins share the same genes but their environments become more different as they age. This unique aspect of twins makes them an excellent model for understanding how genes and the environment contribute to certain traits, especially complex behaviors and diseases.
It was concluded, among many other things, that identical twins are about 85 percent similar for IQ, whereas fraternal twins are about 60 percent similar. This would seem to indicate that half of the variation in intelligence is due to genes.
It is estimated that 1 in 250 natural pregnancies will naturally result in twins. While twin pregnancies can happen by chance, there are some factors that may increase your odds of having two babies at the same time. Let's learn about twins!
However the researchers looked at it, first-borns had, on average, an IQ of 1.5 points higher than second-born siblings, who in turn had a 1.5 higher IQ than third-borns and so on.
Researchers have previously shown that a person's IQ is highly influenced by genetic factors, and have even identified certain genes that play a role. They've also shown that performance in school has genetic factors. But it's been unclear whether the same genes that influence IQ also influence grades and test scores.
There are some family effects on the IQ of children, accounting for up to a quarter of the variance. However, adoption studies show that by adulthood adoptive siblings aren't more similar in IQ than strangers, while adult full siblings show an IQ correlation of 0.24.
It's a common misconception that twins skip a generation in families. There is absolutely no evidence, other than circumstantial, that twins are more likely to occur every other generation.
Quite simply, in early pregnancy, the fetus contained in the gestational sac closest to the maternal cervix was designated as Twin 1, and the relative orientation of the fetuses to each other was then defined as being either lateral (left/right) or vertical (top/bottom).
Identical twins have, for the most part, identical DNA. Because of this, it is difficult to tell them apart by DNA. A standard paternity test won't be able to tell which twin is the true father. Even a more sensitive ancestry-type test (like 23andMe) won't be able to answer this question.
Which twin is older? The oldest twin is the one who is born first. It doesn't matter whether twins are born vaginally or by C-section; the first one out of the womb is considered the oldest. This may be the baby who was labeled baby A during the ultrasounds, but it might not if the other one makes it out first.
Twins not only have a bestie from birth — they also live longer than singletons. And those two factors may be related, according to new University of Washington research.
It has been well documented that twins are shorter at birth than are singletons and that a difference in body height remains for at least a few years after birth (1–4). It is unclear, however, whether the difference persists into adulthood.
Twins don't always share equally. In roughly 30 percent all twin births, one baby will be larger than the other. Some studies suggest that if one of your babies is at least 25 percent heavier than the other, one or both of them may be more likely to have breathing problems or need intensive care.
Assisted reproduction
They increase fertility by stimulating egg production. If more eggs are produced, the chances that more than one egg will be released during ovulation also increase. Among the common ways to get pregnant with twins is through fertility treatment such as in-vitro fertilization (IVF).
Many people believe twins skip a generation, but that's just a myth. The idea that twins skip generations likely comes from the fact that the genetic factors contributing to twins only come from the gestational parent's side.