It seems (from private correspondence) that many people missed the main point of my Cochran, Hardy, Harpending post. (Amritas got it.) So I'll try again.
A while back I speculated about the possibility of a meme plague: that because we decide on our course in life through our reason and emotions, rather than automatically going with "what worked" in the past, cultural transmission can resemble more an infection than an inheritance, and when it does it results not in steadily increasing fitness but in random fitness change, which may well be negative. In fact, all things being equal, since we have been evolving for fitness for so long it is almost inevitable that major changes will result in decreasing fitness. (All things are not equal: our reason/emotions seem pretty at guiding us to survival, but they're not so good at fertility.) As a result, the most insulated from the meme plague, who cleave most tightly to their traditional cultures will almost inevitably have an evolutionary advantage. Those who are in the forefront of western culture like to style themselves as being more "intelligent" than the rest of us. I have a feeling that this is true, and as a result they have lower fertility. Is there an intrinsic connection between high IQ and lower fertility? I think that this too is true. In other words, not only are high-IQ people more suseptable to meme plagues in general, they have a specific bias toward low fertility.
The Cochran, Hardy, Harpending paper (pdf) makes a big assumption: that in an intellectually challenging environment, higher IQ will necessarily result in higher fertility. Why? Because, as they have succinctly put it, with more money you can buy more food. Here's my problem with that argument: It is hard for me to think of any profession or lifestyle in which higher IQ doesn't help you out. Life is full of problems, and IQ helps you to solve them. Therefore, as Cochran, Hardy, and Harpending reason in another context, IQ must have fitness costs as well as benefits, otherwise all populations would have rising IQs. How many really smart people also had large families? Darwin was one, but I can't think of many others. Newton? Einstein? Washington? Jefferson? Tesla? Ford? All these people lived in a time and place when most people had large families, but they didn't.
I have a hunch as to what that is, too. Human beings look for a reason to live. Most of us find that reason in our friends and family, and especially in our children. People with high IQ are apt to find it in their ideas.
Which is all well and good as far as I'm concerned, but it does mean that high-IQ people tend to be less fit, from an evolutionary perspective, than people with lower IQ (up to a point, of course). But what would happen if you put a group of people in an environment so intellectually challenging, that you needed that high IQ merely to survive? Well, the first thing that would happen would be a big die-off. The low-IQ people would have difficulty with survival, while the high-IQ people will have have difficulty with fertility. But, given enough time and diversity, some people will inevitably be somehow able to combine the virtues of both, and evolution guarantees that these people will will increase in number and become the modal type.
Cochran, Hardy, and Harpending seem to assume that given an IQ-challenging environment, high-IQ will inevitably lead to higher fertility. It seems to me that more than that is needed to overcome the problem. One obvious possibility is that Ashkenazis have genetically evolved not only for IQ, but also for some other thing - let's call it the IQ antidote. This is clearly not true: Ashkenazis now, in general, have one of the world's lowest fertility rates. Their genes haven't changed in the last 2-3 generations (in which they have experienced plummeting birthrates). But something has happened. They have stopped practicing Judaism. I think that what Cochran, Hardy, and Harpending have observed is the evolution of a gene-meme symbiosis: the genes provied the IQ, and the memes provided the IQ-antidote which protected them from infertility. In other words, the key factor in producing the high-IQ Ashkenazi profile (along with the other phenomena that Cochran, Hardy, and Harpending point out) may not have been the economic sector in which they specialized: it may have been but Judaism itself.
Posted by David Boxenhorn at June 27, 2005 09:01 PMFertility went up with social class everywhere in premodern Europe - indeed, almost everywhere anyone has ever looked. But not nowadays.
If you want to understand what we assume, read the paper carefully. It's not complicated. We say that a bit of extra IQ boosts income a lot more in a merchant than it does for a peasant farmer (true) and that in premodern euorpe, increased income increased family size - also true.
Ideology and worldview and religion may matter, but high income increased fitness all over the place, from England to China - in the past.
Greg: I am not arguing with you, I am adding my own two bits. Surely you must agree that high IQ must have fitness costs as well as benefits, otherwise it would be high in all populations. The fact that it boosts income more for merchants than for farmers doesn't matter in the long run unless this is true. You yourself have made similar arguments in other contexts.
Of course, this is merely an hypothesis, which I'm not in a position to test, but the high-intelligence, low-fertility stereotype has been around for millennia, so there might be some truth to it.
Now I readed the paper: Perhaps you remember that given the amount of noise in genetical process, I considered that the filter had to be aplied lots of times to separate noise from signal.
Well, the paper proofs that IQ is highly inheritable, so the signal is clear, but still I have some doubts about the filtering process: that is, that higher IQ people are more sucessfull to such extent in Askhenazim population.
Anyway, I would say that the most important force driving the genetical heritage of Askhenzim population is the rate of defection towards mainstream population.
The people leaving judaism could be genetically sucessful outside, but not inside. I mean, Jewish popluation in highly self-selected.
If less-inteligent Jews used to leave Judaism, that could be the piece you need.
Anyway, I disagree about the demographic weakness of Jewish population. You are forgeting the constant flow of Jews into the mainstream population.
Who knows how much Jewish blood we have in Europe (specially here, in Spain).
which I'm not in a position to test, but the high-intelligence, low-fertility stereotype has been around for millennia, so there might be some truth to it.
Probably it is tru for the highest quantuile, but I don´t think it is the case in general.
Probably IQ is positively correlated with fertility, but not very high IQ.
Anyway, all monotheisms encourage fertility. That is not Jewish specific.
Posted by: Kantor at June 29, 2005 10:27 PM PermalinkIn fact, all succesful religous memes are usually very pro-fertility. They depend on their hosts to replicate themselves. In the long run, religion depends more on family transmision than in conversion. So alive religions encourage fertility. Otherwise they would not fluorish.
Posted by: Kantor at June 29, 2005 10:30 PM Permalink