Suppose you have nine brothers/sisters. Your nine siblings will, of course vary in height, weight ... and intelligence. We know how to think about the relationship between the IQ of parents and their offspring (Steve Hsu explains here).
- We take the average of the parents' IQ, and that is the mean IQ of their children.
- The children do not of course have identical IQs, they're not clones; instead they populate the usual Gaussian distribution with standard deviation in the 7-11 IQ point range (rather than the usual population IQ SD of 15). The authors were conservative and used 7.5 in their simulation below.
So Carl and Nick have this table in their paper, from which you can see that the maximum IQ gap within ten children (dimmest to smartest) might be as much as 23 IQ points. Yes, I find that surprising too.
The table is based on a large scale simulation (10 million couples) and what I take it to be saying is this: if you use ten embryos and decide to implant the smartest, then you'll get an average 11.5 IQ point gain over just selecting a random embryo with no pre-screening for intelligence at all.
Is that important? It's the difference between a clerical and a professional job.
If you come from a large family, consider your siblings and consider whether any of this makes any sense.
We already do embryo selection for single-mutation diseases. A fertilised egg (in vitro) is allowed to divide until you have, say, an eight-cell clump - at this stage there is no functional differentiation. One cell is then extracted and its genome sequenced looking for the faulty gene. If the genome is fine, the seven remaining cells are implanted and the embryo grows to term with no ill effects; otherwise, discard and repeat. (It is more complex than this).
For IQ-based embryo selection to catch on we need a predictive model which can take a sequenced genome and predict with tight accuracy the resulting IQ (assuming decent nutrition, no abuse etc). We can't do this now as the relevant genes haven't yet been identified. But that should change within five to ten years. And we need to get the cost right down: doing 10 whole-genome sequences could be pricey.
Apart from the hassle of IVF and any legalistic hurdles, the way would then be open. What might be the consequences? Carl and Nick have a table - click on it to make it bigger.
Just a note about IES on the right-hand side.
"The effectiveness of embryo selection would be vastly increased if multiple generations of selection could be compressed into less than a human maturation period. This could be enabled by advances in an important complementary technology: the derivation of viable sperm and eggs from human embryonic stem cells. Such stem cell derived gametes would enable iterated embryo selection (henceforth, IES):All this and we haven't even mentioned genetic engineering, or CRISPR-Cas9.
1. Genotype and select a number of embryos that are higher in desired genetic characteristics;
2. Extract stem cells from those embryos and convert them to sperm and ova, maturing within 6 months or less;
3. Cross the new sperm and ova to produce embryos;
4. Repeat until large genetic changes have been accumulated."
"Using IES could deliver much more extreme results, and the fixed costs of using IES to produce enhanced embryos could be spread across large numbers of enhanced children. On the other hand, IES would compromise the typical genetic relationship between parents and children. To avoid negative effects of inbreeding, IES would require either a large starting supply of donors, or the expenditure of substantial selective power to reduce harmful recessive alleles. These factors would tend to push towards IES offspring being less genetically related to their parents (though more related to one another), and could reduce the appeal of IES."
I blogged that Toby Young had a piece about this back in September last year.