Books have titles so that readers are tempted to buy them. Such titles are a general indication, and the text will give the further explanations. Neither Plomin nor Harden need be taken literally, but their choice of analogy reveals a general attitude: Plomin sees genetics as being more causal than does Harden. His reference to a blueprint may seem out of place, but genes do unfold in a predictable manner most of the time. How appropriate is the analogy of a lottery?
Here we have to assume that the lottery is an honest one, where every ticket holder has the same chance of winning as any other ticket holder. The chance of a win is winners divided by the number of lottery tickets, and the return on the lottery is the cost of a ticket compared with the probability of getting a particular prize. For example, in the UK there is a lottery (Premium Bonds) in which you keep your stake, but share with others the interest due on your stake. There are £1 million prizes, which tend to attract investor’s attention, and far more common far smaller prizes. How lovely to have a monthly chance of winning a million pounds for a one-pound stake! Yet, however many tickets you buy, the overall return is 1%, so it is not even compensation for inflation. All lotteries are a snare for the gullible.
Is genetics a true lottery? Of course not. Simple examination reveals the analogy to be misleading. Not all outcomes are equi-probable. Intelligence and other characteristics are heritable, and lotteries do not show any effects of inheritance. You pay for a ticket with a fair chance of winning, you do not roll up to claim a prize for privilege. Nor are you rewarded for being a frequent gambler, merely fleeced because of your foolishness. Even your identical twin has no higher chance than you do of winning a real lottery.
Also, people do not mate at random. They make choices. You can only regard your birth as random if you were conceived as a result of a vast masked orgy.
However, some chance is involved in genetic transmission, and that is why the analogy flourishes.
Two bright parents have a higher-than-average chance of getting a bright child, but it is not guaranteed. Birth injuries are one reason, rare mutations another. The other important reason, apparently difficult for some to accept, is that a high correlation is not a perfect correlation. There will be some surprises and disappointments, all as part of the genetic package. Eggs and sperm fuse, and although each parent as a result contributes exactly half of the DNA, the additive genetic inheritance of each child will vary somewhat around the average of the two parents as a result of Mendelian segregation. Kids vary somewhat, though less in families than in the general population.
All parents will have children of similar ability to them because intelligence is 0.8 heritable. Furthermore, instead of a mean absolute difference of 17 IQ points which would obtain if there was zero correlation between parent and child intelligence, their children will have a 12-point mean absolute difference. (I assume a sibling correlation of 0.5 for intlligence, which is the best-supported estimate).
As a rule of thumb, any family will show about two thirds of the variation found between unrelated persons. Children will have different outcomes (and the brighter ones in each family will earn more).
As to regression to the mean, most of the regression will tend to be to their own ancestral family mean. Think of it as a weighted mean of your ancestors, with more recent relatives having greater weight.
If everyone always regressed to the population mean, no differences would ever be found as a result of selective marriages. No family would have a tradition of scholarship nor a particular capacity for banking, or sporting prowess. No bloodline of race horses would matter very much.
To the contrary, endogamous marriage traditions follow the breeder’s equation (which applies to all species), and so long as the characteristic is heritable and confers a slight advantage, it will spread in the descendants, giving them propensities which make them differ from other groups. This is a response to selection, and the more severe the selection over the generations, the greater will be the effect.
Some will hold their breath and dive deeply for pearls, others will calculate their business deals carefully so as to buy those pearls and keep them in their bank vaults.
India has been doing this since at least 300 BC and the differentiation of jatis shows up in genetic studies. The prevalence of rare diseases in India is a testament to the longevity of this practice in the subcontinent. Razib Kahn has explained this in detail.
Thousands of years later the upper stratum of Indian society has a noticeable overrepresentation of ancestry from the Sintashta horse lords of the Bronze Age, an aristocracy that has somehow maintained itself for 4,000 years. This is true in every corner of the subcontinent with Brahmins in particular, and genetics indicates that many of the Brahmin groups have had a coherency that dates back thousands of years. They monopolized elite positions in a primitive agro-pastoral Iron-Age society, and they remain overrepresented in elite positions in a world where India is slouching towards its destiny as an advanced technological society. This is a miracle of continuity and stability which the British could never have invented. Some things about India are truly eternal.
So, is having children a gamble? Not really. It is not a true gamble in the sense that everyone has equi-probable outcomes. For example, if every newborn was sequestered and then put up as a lottery prize for the general public, then that would be a real gamble. Horrible, but a gamble. (Sometimes I fear that only a policy as severe as this will ever satisfy social engineers).
In the real world, your children will be very much like you and your partner, with abilities very much like yours. Your children will vary around the parental mean with somewhat smaller variation than that observed in the general population. They are children, not clones, so somewhat different but very like you, and more like each other than the general population.
So, not a guarantee, but a strong likelihood.