<p>In addition to MariaAnt's good contribution, let me take another angle. You wrote:</p>

<blockquote>
  <p>Studies comparing identical and fraternal twins, or occasionally identical twins reared apart have mostly concluded that there is a pretty <a href="https://en.wikipedia.org/wiki/Heritability_of_IQ" rel="nofollow">high heritability of IQ</a>. These studies, in particular the identical twins reared apart studies, imply that someone with the same genes but different environment would have a highly similar IQ.</p>
</blockquote>

<p>This is a good example of why it is always good to be as quantified as possible in one's statements. What is "high" in this case? What is "highly similar"?</p>

<p>If you follow that Wikipedia link you provided, it actually does make an attempt to quantify the heritability:</p>

<blockquote>
  <p>Estimates in the academic research of the heritability of IQ have varied from below 0.5 to a high of 0.8 ... <strong>The general figure for heritability of IQ is about 0.5 across multiple studies in varying populations</strong>.</p>
</blockquote>

<p>If we can take 0.5 as a reasonable value, that is a healthy correlation, but it is not 1.0. Even if the actual value should be more like 0.8, that is still not a perfect correlation. That is consistent with the model that genetics is not the only factor that might go into the observed differences in IQ--which, given what we know about training, nutrition, and the brain, essentially <em>has</em> to be true. The Flynn Effect's finding and interpretations of it that refer to an environmental component to IQ is consistent with this view.</p>

CC BY-SA 3.0
2015-08-15T18:08:03.833Z
2015-08-15T18:13:53.243Z
2015-08-15T18:13:53.243Z
Chelonian
<p>Studies comparing identical and fraternal twins, or occasionally identical twins reared apart have mostly concluded that there is a pretty <a href="https://en.wikipedia.org/wiki/Heritability_of_IQ" rel="nofollow">high heritability of IQ.</a> These studies, in particular the identical twins reared apart studies, imply that <em>someone with the same genes but different environment would have a highly similar IQ.</em></p>

<p>The Flynn effect, though, shows that people's average IQ is increasing, around 15 points every 50 years. All the explanations I have encountered (like <a href="https://www.ted.com/talks/james_flynn_why_our_iq_levels_are_higher_than_our_grandparents" rel="nofollow">this one</a>, from James Flynn himself) focus on environmental reasons for this, for example culture, education, perhaps better health. They seem to imply that <em>someone with the same genes in a different environment might have a very different IQ.</em></p>

<p>Are these two in direct contradiction with each other, or is there some way of reconciling them?
If they are mutually exclusive, with which does the scientific consensus lie?</p>

<intelligence><iq><genetics><nature-nurture>
Is the Flynn effect in conflict with other studies of intelligence heritablity?
clarkep
# Is the Flynn effect in conflict with other studies of intelligence heritablity?

(Asked by: username_0 on 2015-08-14)

Studies comparing identical and fraternal twins, or occasionally identical twins reared apart have mostly concluded that there is a pretty [high heritability of IQ.](https://en.wikipedia.org/wiki/Heritability_of_IQ) These studies, in particular the identical twins reared apart studies, imply that *someone with the same genes but different environment would have a highly similar IQ.*

The Flynn effect, though, shows that people's average IQ is increasing, around 15 points every 50 years. All the explanations I have encountered (like [this one](https://www.ted.com/talks/james_flynn_why_our_iq_levels_are_higher_than_our_grandparents), from James Flynn himself) focus on environmental reasons for this, for example culture, education, perhaps better health. They seem to imply that *someone with the same genes in a different environment might have a very different IQ.*

Are these two in direct contradiction with each other, or is there some way of reconciling them?
If they are mutually exclusive, with which does the scientific consensus lie?

**Tags:** intelligence, iq, genetics, nature-nurture


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## 1 answers

### Answer by username_1 on 2015-08-15. Score: 3

In addition to MariaAnt's good contribution, let me take another angle. You wrote:

> Studies comparing identical and fraternal twins, or occasionally identical twins reared apart have mostly concluded that there is a pretty [high heritability of IQ](https://en.wikipedia.org/wiki/Heritability_of_IQ). These studies, in particular the identical twins reared apart studies, imply that someone with the same genes but different environment would have a highly similar IQ.

This is a good example of why it is always good to be as quantified as possible in one's statements. What is "high" in this case? What is "highly similar"?

If you follow that Wikipedia link you provided, it actually does make an attempt to quantify the heritability:

> Estimates in the academic research of the heritability of IQ have varied from below 0.5 to a high of 0.8 ... **The general figure for heritability of IQ is about 0.5 across multiple studies in varying populations**.

If we can take 0.5 as a reasonable value, that is a healthy correlation, but it is not 1.0. Even if the actual value should be more like 0.8, that is still not a perfect correlation. That is consistent with the model that genetics is not the only factor that might go into the observed differences in IQ--which, given what we know about training, nutrition, and the brain, essentially *has* to be true. The Flynn Effect's finding and interpretations of it that refer to an environmental component to IQ is consistent with this view.


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