Are twins or triplets (or more) really less intelligent on average?

I heard that twins turn out with lower IQ, on average, than single children born, because the maternal nutrients sent in utero are split into two

Is this true – any evidence of it? Einstein had no twin, but of course that is most likely explained by the odds.

Wow. Waiting for someone from the medical field but I am not aware of any study showing that multiple births produce less intelligent offspring. What would happen with sextuplets? While these babies tend to be much smaller than average, and often are born prematurely, and often have serious medical problems to deal with, I’m not aware of a low IQ being one of the issues these parents had to deal with. But I could be wrong…

I went to school with 6 sets of twins in my graduating class. Only one set was identical, I think.

Two of the girls (not of the same pair) were in the top 10 of our graduating class. One of the girls’ twin was towards the bottom and the other I think was more towards the middle.

The other 4 sets, I’d guess, were average students.

Other than the well-known fact that Bokanovskification is associated with lower intelligence, I got nothin’.

I remember reading in my high school psychology textbook that twins were, on average, less intelligent than single births. The explanation the book gave was that twins tend to get less individual attention from their parents than singly born kids did.

Although I have no cites, this is my recollection as well. At least it is consistent with studies that I am aware that have shown that intelligence of offspring diminishes with each subsequent birth. Not only do the later offspring score lower, but they also have a tendency to reduce the intelligence of older siblings. Some may question the validity of these studies. Here is an overview: Does Birth Order Affect Intelligence?.

Multiples are also more likely to be born premature, which increases the chances for all kinds of problems that could affect their cognitive development.

My Dad was not only a twin but also one of the smartest people I’ve known…for what it’s worth.

This is only anecdotal evidence, but:

[ul]
[li]I have a twin sister.[/li][li]I was the ninth child born into a family of 10 (my twin came in 10th place, nine minutes after me)[/li][li]I’m the only member of my family who has a PhD[/li][/ul]I’m not sure if this means that I just happen to deviate from the averages for twins, as well as for children born late in the birth order of large families, or if it’s a sign of the declining value of a PhD.

Twins tend to be of lower birth weight than non-twins:

http://en.wikipedia.org/wiki/Twin

Babies of lower birth weight tend to be of lower intelligence:

http://en.wikipedia.org/wiki/Birth_weight

I would thus expect twins to be of lower intelligence on average, but I can’t find any study in some quick searching than relevant to this question.

G-- I’m starting to think that we are the same person. I have a twin sister, and I’m the only in the family with a PhD (only 4th kid out of 5, though, and I’m the younger twin). And we’re in the same field. . . as for the value of a PhD in that field. . .

It is probable that on average, given the prematurity of most twins, that things go wrong a bit more. Which means that anecdotal evidence means little, and very large numbers mean a lot.

I are a twin annd eet hazn’t kawsed mee eny problemz.