Is a big family bad for IQ?

A century of studies on family size and IQ have consistently come up with an unnerving conclusion: on average, across populations, (rather than individual families, who may be exceptional), a big family, means a lower average IQ of each family member. This is not one, isolated study showing this: there are innumerable studies over a century.

Now, what is the reason for this correlation? There are two obvious possibilities. One is that as the family size increases, the parents have less time to give attention to individual children, less money to pay for education and, therefore, the greater the number of children, the less stimulation each child receives. The other possibility is that large families are the product of low IQ parents, of lower social economic class - and indicate differential inheritance, rather than a difference caused by family size, per se.

Traditionally, larger families HAVE been the product of lower socioeconomic classes - and so these studies may be reflecting differences of income and educational opportunity rather than an effect of family size.

On the other hand, as I pointed out in my earlier post, "On being a father of three", http://scientific-child-prodigy.blogspot.com/2007/01/on-being-father-of-three.html, having a larger family does mean less time to apportion to each child, with probable consequences for their intellectual growth.

So, given this, what is one to do with regards to family size? I have three children and would like more - so in this I have joined the 28 per cent of American parents with three or more children. A recent report stated that the nature of these parents is changing: many more of them are from wealthier, better educated families than before. This could be the beginning of a good trend, therefore - of brighter parents, having more children. Are these families condemning their children to dullness? I don't think so. I think the genetic effects are stronger than the environmental and will still allow their children to be bright. Why do I think this? Well as I pointed out in an earlier post on Genius IQ and Genetic Inheritance, http://scientific-child-prodigy.blogspot.com/2006/10/genius-iq-and-genetic-inheritance.html, the IQ of parents correlates 0.8 with the adult IQ of their children. That argues a strong role for their genes, and a much smaller role for the environment provided.

If you have a gifted child, it is likely that you could have another if you chose. That your family is getting bigger and your attention would be diluted among more children is probably a smaller factor than the fact that you already have what it takes to make a gifted child, genetically.

Then there is the matter of chance. Which genes a child inherits is random: they will get a selection of half the genes of each parent. Anything can happen in that process - giving a spectrum of results. Yet, if you have more children, you also have more of a chance that one of them will get the right mix of genes and turn out to be gifted - if that is what you want in your child.

It is a difficult matter, family size, for there is no denying that, as the family gets bigger that there is a greater division of attention, time and money. It is, I feel, up to each individual to judge the weight of each of the issues and decide the question: just how big do you want your family to be?

I know the answer for me: at least one more: after three boys, it would be nice to have a girl, too!

(If you would like to read of Ainan Celeste Cawley, a scientific child prodigy, aged seven years and one month, or his gifted brothers, please go to: http://scientific-child-prodigy.blogspot.com/2006/10/scientific-child-prodigy-guide.html I also write of child prodigy, child genius, adult genius, savant, the creatively gifted, gifted adults and gifted children in general. Thanks)