I am a graduate student working on a Ph.D. in cognitive psychology, and I'd like to allay everyone's fears about these articles.

Yes, they found a difference between older and younger sibling's IQs, but that difference is hardly a large one.

Let me explain a bit about the way IQ works.

Based on a large database, everyone's IQ is normalized, so that the mean (or average) is 100. Additionally, the standard deviation is set to be 15. A standard deviation is just a measure of how random people's IQs are. Let me explain that a bit more. We can expect that 68% of the population has an IQ within one standard deviation of the mean. 96% of the population is within 2 standard deviations of the mean. In other words, 68% of the population has an IQ between 85 and 115, and 96% have an IQ between 70 and 130.

A difference of 3 points, or one fifth of a standard deviation is a meaningless difference. I might expect that same difference depending on whether or not I had my morning cup of coffee before taking an IQ test.

That's not to say that there isn't a difference. I'm just saying that the difference is so small, its practically meaningless.