Welcome back. In this third module in unit six, week six, I'm really going to sneak in a very brief discussion of something that we discussed a little bit earlier in the course, in week three. And that is, to what extent the heritability of a trait is related to the malleability of a trait. And the bottom line, and we discussed this in week three, is that there really is no necessary relationship between the two. That is, something can be heritable, but malleability, that is, whether or not the trait can change in response to environmental intervention, malleability can still exist, even if a trait or phenotype is highly heritable. And the example I gave you in week three, and I'll just briefly touch on this again here today, was height. And this is data from again Kari Silventonin from Finland, where he's looked at various large scale twin studies of height. And not surprisingly in both women and men height is a highly heritable trait. Heritability estimates approach 80%. Nonetheless, and I gave you this data before, we know that over the last 100 years or 150 years individuals have been getting taller over time. And they have been getting taller over time, not because their genomes have been changing, but rather because the environment is changing. Our genomes don't change rapidly enough to actually account for what is about 10 to 15 centimeters on average increase among various European populations over the last 150 years. The same thing is going on in non-European populations but the data coming out of Europe is just a little bit easier to work with. And it's easier to work with because the data come out of conscript boards where large proportion of the population in, in, in most cases, just males but, nonetheless, a very high percentage of males undergo a conscription evaluation at age 19. And so we can see for one category after the other, the average height in the populations have been increasing. And again, over an extended period of time, the increase is quite dramatic. Height is highly heritable. It does not mean that height is non-changeable. The change that we see over time really reflects environmentally induced change in height. What we're talking about this week, though, is not height but general cognitive ability. And I previously gave you three different studies that aimed to estimate the heritability of general cognitive ability. And they all converge on an estimate of about 50%. So it's certainly not as high as the heritability estimates for height, but it's quite high, it's still 50%. Does that mean height, I'm sorry, does that mean general cognitive ability is not malleable? Of course not. And in fact, the same studies, or the same populations that are documenting an increase in height actually are documenting increases in general cognitive ability over successive cohorts. And the person that really first observed this is a political philosopher from New Zealand named James Flynn. And his observation has actually been named for him, it's called the Flynn Effect. And what Flynn observed is the average IQs in populations have increased at a rate of about three to five IQ points per decade. Now that's actually quite a dramatic increase. But of course the increase in height was also quite dramatic. Here I've redrawn some of the data that James Flynn uses to draw this conclusion that our IQs are increasing over time. The data again are being drawn, it's kind of a bias sampling of cultures, but they're cultures that represent cultures where, there are man, there is mandatory conscription and essentially the same IQ test has been given over and over again, to successive cohorts of 19 year old males. Other data that we have show the same phenomena going on with women, as is illustrated here for men, and in countries that are non-European. But the data are just a little bit cleaner and easier to understand when we look at that European conscript data. So the way Flynn has represented the data here is again the year that they actually showed up at the conscript board is along the horizontal axis. The average IQ is along the vertical axis and he scaled things so that in the last date from which they were reporting data, from the particular country, it scaled to have a mean of 100, which is the typical average IQ. So the point there is that these all top out at 100 by design, by the way he analyzed or structured the data and you can't really compare one country to the other. You can't say anything about Brit, Britain versus Belgium. The point that I want to emphasize here is just like for height, IQs have been increasing, again, about three to five points per decade in one country after the other. In all the countries here, we see a very similar linear increase in average IQ. Again, this is for male conscripts in predominately European countries, but the same thing is going on worldwide with both men and women. And the increases are quite dramatic. Let's just pick one of these. So in England, in Britain, Great Britain, I'm sorry, the average IQ has increased from 73 to 100 over a 50 year period. So that's about five IQ points a decade. That's 27-point increase over fifty years. That's really a phenomenal increase. I would imagine some of you are thinking, well, come on, that can't really be true. It can't be that the average individual, in 1942, if they took the test in 1992, would score at an IQ of 73. We really couldn't be increasing in our actual intelligence at that rate. Probably some of the increase in IQ is just due to we've become more sophisticated and knowledgeable about taking tests, but probably, at least, many psychologists, and I would count myself in that group, believe that we really have increased in our collective intelligence over the last 40 or 50 years. That people are, on average, smarter today than their grandparents or parents were in previous generations. Why is that? Probably some of the things that led to an increase in height are also leading to an increase in average intelligence. Things like better public health measures, but probably also things like better educational systems, better access to education, going further in school, are contributing to this increase in IQ. The point I really want to emphasize here is the point that virtually every behavioral geneticist believes. It's a misinterpretation of the research we do to claim that, if we show something is heritable, that implies something about whether it's likely to be changeable. Heritability and malleability are not necessarily linked. Next time I'll talk about gene environment interplay in studies, behavioral genetic studies on general cognitive ability. Thank you. [SOUND] [BLANK_AUDIO]
