Twin Co-Twin and Twin minus Co-Twin (IQ Question)

[Dooga Blackrazor]

I am reading a book that is a bit old, and it presents studies by Record and Myrianthopoulos about twin IQ differences. Record argues that the IQ of twins who had their twin die pre-natal is higher than twin pairs. Myrianthopoulos did a similar study with conflicting results and low variances.

I am learning toward Record, but I am wondering if further studies have been done on the matter.

Thanks

 

[selfAdjoint]

Were these monozygotic ("identical") twins?

Jensen, in The g Factor references Myrianthropoulos only in connection with a low birth weight study in connection with black-white IQ differences [note 95 in Chapter 12, Population Differences in g: Causal Hypotheses]. He doesn't reference Record at all.

 

[Moonbear]

I guess a lot would depend on what stage of development the twin died. Especially if it's an old study, I would suspect part of the explanation could be attributed to nutritional effects in utero. I don't know whether it's different now that women know they are bearing twins early enough in pregnancy to adjust their nutrition for feeding two fetuses, but it used to be that twins were smaller than singletons at birth. So, if a twin dies in utero, it would make sense to me that the remaining twin would be developing more like a singleton, with a greater birth weight.

I don't know if this is the explanation though, I'm just guessing that this would seem like a reasonable explanation. Did the study take into account birth weight?

On the social side, it also might make a difference if parents have to divide their time between two twins vs nurturing only one; twins are especially demanding to raise, particularly while still infants, so neither may get quite as much stimulation while young as a singleton would. And again, if it was a very old study, it could have been at a time when fathers didn't contribute as much to child care, so only one parent was providing the majority of interaction and stimulation to the infants during critical developmental stages.

Did either look at factors such as birth weight or time spend interacting with parents, or types of activities engaged in while infants?

 

[Dooga Blackrazor]

Monozygotic twins. Sorry about the wait - been terribly busy. Moonbear, that is an interesting hypothesis regarding birth weight. However, in Record's study, the twin minus co-twin weight was less. 2.28 kg to 2.52 kg.

The singletons were stillborn, died at birth, or died within a month of birth.