Sex Differences in the Distribution of Mental Ability. Good bookmark for those interested in psychometry.

Nice to see this kind of thinking percolating into the mainstream:

The second effect of the literacy obligation was to drive a lot of Jews away from their religion. [stupid Jews become Christians or Muslims -Razib] Botticini and Eckstein admit that they have little direct evidence for this conclusion, but there's a lot of indirect evidence. First, it makes sense: People do tend to run away from expensive obligations. Second, we can look at population trends: While the world population increased from 50 million in the sixth century to 285 million in the 18th, the population of Jews remained almost fixed at just a little over a million. Why were the Jews not expanding when everyone else was? We don't know for sure, but a reasonable guess is that a lot of Jews were becoming Christians and Muslims.

So—which Jews stuck with Judaism? Presumably those with a particularly strong attachment to their religion and/or a particularly strong attachment to education for education's sake. [the smart Jews remain -Razib] (The burden of acquiring an education is, after all, less of a burden for those who enjoy being educated.) The result: Over time, you're left with a population of people who enjoy education, are required by their religion to be educated, and are particularly attached to their religion. Naturally, these people tend to become educated. And once they're educated, they leave the farms.

Read the whole thing over at Slate. And before godless chimes in, the same kind of article could be applied to priestly elites the world over, Brahmins, families that form the ulema and Protestant clergy. Is it any coincidence that these groups tend to become the intelligensia once they become secularized?

Update from Jason M: The Slate article summarizes the work of Maristella Botticini and Zvi Eckstein. For a fuller treatment of the theory you can read their entire original paper (PDF) From Farmers to Merchants: A Human Capital Interpretation of Jewish Economic History.

Update from Razib: Also, check out the thread over @ Yglesias' blog on this topic.

Further information from Razib: Readers might be interested in the National Jewish Survey data (PDF). Look at the traits for "Jews of other religions," and note the contrast in educational level and income with "Jews by religion" and "Jewish with no religion." This might not apply historically, but it is interesting in the American context.

Zack Ajmal has a great post on arranged marriage and all that jazz.

On an aside, I think arranged marriages tend to be a trait of dense agricultural societies, which means most of written history. Studies, from what I know, of hunter-gatherer peoples indicate a more chaotic and free-form attitude toward love & marriage, perhaps explaining the tumult that is the characteristic of human relationships [1].

On a related note I got this email this week:

First, I think that I have brought up the need for serious cost-benefits analysis of the effect of biological honesty on a multi-ethnic society.

Second, and more practically, your discussion of the poor marital prospects of dark-skinned subcontinental women drew my attention. From what I have read, arranged marriages are actually rather successful on average. I know two or three semi-ascetic men who simply find the American dating scene too painful, time-consuming, and banal for them to put in the effort. I suspect that many of them could recieve substantial psychological and economic benefits from marrying any submissive, hard-working, high IQ, english speaker. In the process, they would improve the economy and gene-pool of the US and provide a major life-opportunity for someone who might otherwise have poor marriage prospects. Do you think that this would be a realistic, low-effort endeavor? Do you think that I should encourage my friends to consider this possibility. How would you recommend I sell a suggestion like this? In return for any assistance, if this works out I'll be on the lookout for smart pretty blonds who like your appearance and writing (post a photo of yourself) :-).

I suggest a brown matrimonial site (Warning! Brown chicks are short). Oh, and as I told my correspondent the last service will not be necessary.

P.S. - Did anyone else find the relationship between the dirty Irish coach and the brown chick in Bend it Like Beckham creepy? They especially didn't depict brown guys very well (the one cool brown guy is gay!).

[1] If our evolutionary heritage involved a long period of patrilocal & patriarchal systems where women were kept sequestered from the general male population I wonder if jealousy would be as much of a factor in the male psyche since he would have to worry less about other men cuckolding him. In fact in societies where women are cloistered the men doing the cuckolding are even likely to be near blood relatives, reducing the genetic cost of such acts to the legitimate husband.

There is an interview with John Maynard Smith in the current issue of New Scientist (14 June). Among other things, he says:

"Eugenics is a dirty word, but I don't think it should be. I think we are going to have to think quite seriously about it. The words 'eugenics' and 'fascism' are regarded as almost synonymous and I think that's just plain silly".

He also reveals that he has 'just finished' writing a book on the evolution of animal signals. But he says he is currently 'working on tuberculosis. There are a number of problems that arise from the evolution of antibiotic resistance'.

He also thinks the most exciting issues in evolutionary biology concern the theory of development. He believes there is now enough detailed information on developmental processes to begin work on a theory of the genetic regulation of development, by analogy with computer programming. 'It's tremendously exciting! If I were 40 years younger, this is what I would be doing.'

John Maynard Smith is 83.

DAVID BURBRIDGE

I have at last got my hands on C. Capelli et al.: A Y Chromosome Census of the British Isles, Current Biology, vol. 13, 979-984, 27 May 2003.

Capelli et al. took DNA samples from men in 25 small towns around the British Isles, excluding men whose paternal grandfathers were born more than 20 miles away. For comparison they also took samples from Norway, Denmark, North Germany (Schleswig-Holstein), Friesland (Netherlands), and the Basque region of Spain. Using comparison of Y chromosome haplotypes, the Danish, North German and Frisian samples are all closely similar to each other, but the Norwegian sample is significantly different from these, and the Basque sample is widely different.

In a Principal Components analysis the Irish and Welsh samples (with one exception) cluster together with the Basque sample, supporting earlier findings. As the Basques speak a pre-Indo-European language, this suggests that the Irish and Welsh (so-called ‘Celts’) have a largely pre-Celtic genetic ancestry, possibly going back to the Palaeolithic. In Britain, the Orkneys, Shetlands, Western Isles, Isle of Man, and Cumbria (Penrith) show a clear Norwegian input, as expected. Elsewhere in mainland Britain there is no obvious Norwegian input, but varying degrees of German/Danish ancestry. Scottish mainland sites are intermediate between English sites and the ‘indigenous’ (Welsh/Irish) ones. However, all the English and Scottish sites show some ‘indigenous’ ancestry. The German/Danish component is strongest in eastern England and weakest in England south of the Thames.

Most of this is unsurprising, but there are two more controversial conclusions.
One is the claim that ‘the results seem to suggest that in England the Danes had a greater demographic impact than the Anglo-Saxons’. This is based on the finding that the German/Danish element is strongest in areas like Yorkshire that are known to have been settled by Danes. The conclusion seems to me a non-sequitur. The areas settled by Danes were the areas most exposed to invasion from Denmark and North Germany, and they got a double dose of German/Danish genes: first from the Angles, then the Danes. It would be very surprising if they did not have the strongest German/Danish element.

The other controversial conclusion is that the German/Danish element in southern England (south of the Thames) is limited, and that the male ancestry of this area ‘appears to be predominantly indigenous’. This may be true, but I would want to see it replicated with different samples and methods before taking it as firmly established. It should perhaps be noted that the samples with the smallest German/Danish element all come from areas (Wessex, Sussex, and Kent) reputedly settled by Saxons and Jutes, while the samples with larger German/Danish elements come from areas settled by Angles (East Anglia, Mercia and Northumbria). Conceivably there was already a genetic difference between these three ethnic groups before migration, though this does not seem particularly likely, as they all came from much the same area of Northern Europe.

As Capelli et al. recognise, their results seem to conflict with those of Weale et al., ‘Y Chromosome Evidence for Anglo-Saxon Mass Migration’, Molecular Biology and Evolution, 2002, vol. 19, pp.1008-21, which found a sharp distinction between central English and Welsh populations, but no significant difference between the English population and a Frisian sample. This discrepancy needs to be reconciled.

As I am a historian and not a geneticist it may help if I outline the historical evidence on the ethnic origins of the English. There is no dispute that British Celtic) elements were predominant in Cornwall and Cumbria, where Celtic languages survived long after the Anglo-Saxon invasions. There is also good evidence of British elements surviving in Kent and Wessex (see esp. Myres, ‘The English Settlements’, pp.147-73). But beyond that, there has been controversy since Victorian times. At one extreme, which I call the ‘Wipeout’ theory, it is believed that Celts were virtually exterminated or expelled by the invading Anglo-Saxons. At the other extreme, which I call the ‘Upper Crust’ theory, the Anglo-Saxons took over as a ruling elite but left the peasants largely untouched (rather like the later Norman Conquest). And of course there are intermediate positions.

The main lines of evidence are as follows:

Written sources: the main sources - Gildas, Bede, and the Anglo- Saxon Chronicle - make it clear that invaders from the Continent took political control of what is now England, and that in many places there was violent conflict between the invaders and native forces. But there are no reliable written sources on the numbers and proportions of different groups.

Language: the Old English or Anglo-Saxon language, in its various forms, is purely Germanic in its grammar and vocabulary, with no discernible Celtic element. If the Celts learned English, they learned it very thoroughly. The later Danish settlements strongly influenced the form of Old English spoken in eastern England, but did not replace it.

Place-names: the names of major towns and rivers often show some derivation from Celtic or Romano-British names, but the names of rural settlements are overwhelmingly Germanic (Anglo-Saxon or Danish), except in western England, where there is a ‘cline’ of increasing Celtic influence. However, there have been controversial claims that some Anglo-Saxon names have disguised Celtic origins.

Continental evidence: before the Anglo-Saxon settlement of England there were people known as Angles in northern Germany, and after it there weren’t. Around the same time, the Armorican peninsula was settled by Celtic Britons, to the extent that the area became known as Britain (Bretagne or Brittany). This certainly looks like a mass displacement of populations.

Religion: late Roman Christianity and Celtic religions disappeared from England and were replaced by Anglo-Saxon paganism until Christian missionaries from Ireland and Rome arrived.

Archaeology: there are few recognisable remains of any kind from the 5th century. After that, archaeological remains are mainly Germanic in style. It was formerly assumed by archaeologists that a change in style of this kind involved a migration of people, but the recent tendency has been to assume that styles change by ‘cultural diffusion’ or elite influence. Sometimes archaeologists seem to forget that ‘no conclusive proof that A’ is not the same
as ‘conclusive proof that not-A’.

Social structure and customs: the evidence from Anglo-Saxon poetry, laws, etc., is of a Germanic/Scandinavian society and customs. However, some sources do refer to ‘wealh’ (Welsh) inhabitants, who are presumed to be surviving Britons. The laws of Ine, king of Wessex in the late 7th century, make it clear that ‘wealh’ people could be either free or slaves (theow), and that they could belong to ‘wealh’ kinship groups, which implies survival of more than isolated individuals. Also, some charters and other documents refer to substantial numbers of slaves. (It complicates matters that the word ‘wealh’ itself, which originally meant ‘foreigner’ or ‘stranger’, may sometimes be used to mean ‘slave’, implying status rather than necessarily ethnic origin.)

The positive evidence, so far as it goes, seems to me consistent with something closer to the ‘Wipeout’ theory than the ‘Upper Crust’ theory, though with survival of ‘wealh’ populations in varying proportions. The advocates of the ‘Upper Crust’ theory rely heavily on an ‘argument from impossibility’: it is impossible, they say, that a relatively small number of Anglo-Saxon invaders can have wiped out a much larger Romano-British population. However, I think this is a misunderstanding of the invasion scenario. Roman-British society rapidly broke down when the Romans left. Even without invasion there would have been a population crash. The Romano-British were virtually defenceless apart from mercenaries who were themselves mainly Germans (Saxons), and quick to invite their relatives over to share the spoils. To destroy a defenceless population, it is not necessary to kill them individually. Just take a few captives in the first village you come to, skin some of them alive in the market-place, and let the rest of them go to spread the news. A wave of panicking refugees will spread out in all directions, and starvation and disease will do the rest. For analogy, suppose you heard that Martians with invincible weapons and sadistic habits had landed twenty miles away. You would run like buggery!

However, the feasibility of a scenario does not mean it is true. Further genetic evidence may finally resolve the controversy. If it is in fact proved that the ‘Celtic’ element was predominant in southern England, this would have interesting implications for cultural history and evolution, for it would show that a complete change of language and culture can be imposed by a dominant minority, in an illiterate pre-industrial society, and in a short period of time.

DAVID BURBRIDGE

A few years back a study indicating that people are attracted to faces like their own came out. One thing that I neglected to mention when I blogged this last was the following:

What Perrett found was students who were born when their parents were older than 30 overwhelmingly preferred older faces. Students whose parents were younger when they were born selected younger faces as more attractive.

Those with older parents, Perrett said, "were less impressed by youth."

Perrett's colleague Anthony Little, also of St. Andrews University, has since followed up with another study looking at hair and eye color. His results show that people generally prefer faces with the same eye and hair color as their parent of the opposite sex (as in a woman's father or a man's mother).

The implication of the last finding for interracial relationships and children of mixed heritage is intriguing. Since most Asian-white relationships in the United States are female-male respectively, it would be interesting to see the pattern of spousal choice of men and women of biracial origin. The above results indicate that Eurasian women in the United States should prefer white men while Eurasian men should prefer Asian women as partners. It would probably be best to look at Hawaii to see if there is a pattern since the racial mix there is balanced enough that there is a wide choice of spouses.

The most recent Economist has a survey of the Nordic countries and states "In Sweden as a whole, one in four people is foreign-born or of foreign parentage."

Our Islamic Fine-Tuning Project is an introduction to a book titled Progressive Muslims. I wish them good-luck, but I suspect that they're the Spinozas of their age, ahead of their time....

Ibn Warraq, the world's only professional ex-Muslim (that I know of), has an article out debunking Edward Said [1]. A much shorter version is also there for those who aren't footnote hounds (thanks G Factor). I read Orientalism and found it rather uninteresting (and yes, there are obvious errors about Muslim history that makes you wonder what kind of expert this dude is-he's an English professor actually!). Yeah, Orientalists did serve Imperialism and Racism and all that, and perhaps Bernard Lewis still does in some way, but that doesn't mean that all they say is incorrect. I frankly don't trust Arabs to report objectively on their societies at this point-though non-Arab Muslims might be a good compromise. To also be equal opportunity I've got to ask, what went wrong with Bernard Lewis? His last two books, What Went Wrong & Crisis of Islam seem to be nothing more than compilations of his ramblings on the Charlie Rose Show [2]. His earlier books, like The Middle East, are much more dense and pre-date his ubiquitous appearences on late night PBS talk-shows, they show how orientalism should be done.

[1] Folks like Salman Rushdie weren't very Islamic to begin with and their books deal in broader topics than Islam. Also, Warraq has a new book out titled Leaving Islam.

[2] Charlie Rose is to Bernard Lewis what Larry King is to Marlon Brando, the guy needs to chill on his platonic crush big time.

Check out this article in Salon titled Black like me -- but not too black which discusses the tensions that exist among African Americans who want a nose job. The author hits some good points, you'd have to be a fool to deny that the European aesthetic ideal is dominant today, that many (most?) non-white people would probably change aspects of their physique to more closely fit that norm (by this, I don't mean that they would become white, just fiddle enough at the edges to be less ethnic looking without morphing into freaks like Michael Jackson). One thing that annoyed me is that the author notes that she is "light skinned" and has "fine hair." Her broad African nose apparently gives her cred to speak on this topic, but I really am more curious about what more obviously African looking people think about cosmetic changes in appearence. The reason I say this is that there are studies out that indicate that racial bias and prejudice falls harder on dark-skinned and often more African featured blacks. These are the people that would stand to benefit the most from cosmetic surgery and skin lightening creams that worked. Light skinned blacks on the other hand often seem to have a bit of both worlds, using the hypodescent definition of African Americans to claim the mantle of "oppressed," but being able to interact more easily with white Americans because of a greater phenotypic resemblence [1]. Light-skinned blacks have a social reason to oppose the widespread use of techniques to melt away distinctive African features, because they themselves are born with those traits and lose their advantage over their skillet-blonde cousins.

George Schuyler even wrote a novel, Black No More, which explores the absurd twists and turns that result when a black doctor invents a procedure to turn blacks "white" [2]. We talk a lot on this blog about "genetic engineering," but it seems to me that cosmetic procedures that alter phenotype rather than genotype (germline) will become cheap even sooner-and those who argue that polygenic phenotypes like IQ will not be amenable to manipulation can't dispute that skin coloration or nasal width are easy to change with brute force methods. As C. S. Coon predicted back in the 1960s racial identity might become more optional, causing a host of social changes. Of course if a genuine skin lightening cream that was affordable came on the market Asia would be the #1 region to market it.

[1] In criticizing his ex-comrade Shelby Steele, ex-black conservative Glenn Loury notes, "Shelby is half-white, his children are 1/4 white, he can afford to oppose affirmative action as he lives in a white world...." Similar criticisms have been thrown at John McWhorter, enfant terrible of the black neocons, as his combination of light skin, Caucasian features and "white" accent don't endear him to more "authentic" spokespersons for the race. Of course, both Steele & McWhorter accept hypodescent, I remember Steele joking about how his children go to black churches and people for some strange reason think they are white just because they look white (This was on C-SPAN's BOOKNOTES, the host seemed kind of confused as to what Steele meant).

[2] Read Interracial Intimacies for a detailed exploration of Shuyler and his family as well a good summation of Black No More.

Over at Tacitus godless & I have been having a little dialogue with dissenters from the position that GNXP offers a different and valid viewpoint than normally mooted in "respectable" circles. In any case, one of the commenters brought up the Eyfurth study that showed that black-white mixed children in post-World War II Germany had about the same IQs as white children whose fathers were also servicemen. The study is very interesting and suggestive, because it contradicts the Minnesota Transracial Adoption Study that showed interracial twins adopted who were of mixed-race had IQs between that of black and white adoptees.

Jensen in The G Factor has a few quick responses:

• The fathers' IQs are not accounted for, and it could be that both groups of servicemen, black & white, were not representations of the mean in their parent populations. Jensen notes that 30% of blacks vs. 3% of whites were rejected during preinduction because they failed mental tests.
• Factors that influenced assortive mating were not tracked. For instance, low SES German women might have had equal preferences for high IQ black officers and low IQ white privates because intelligence could have overcome racial bias in the former case while there was a preference for the latter because they understood that their children might be less ostracized by society if they were not racial minorities.
• The tests were taken during pre-adolescent years when correlation between IQ scores and genotype is lower than in later years.
• Heterosis, or hybrid vigor, could have bridged some of the gap.

In any case, let's ignore these factors, and address the topic. Flynn, of the Flynn Effect fame, suggests that something in American society (prejudice, racism, etc.) might be influencing parents to treat their black adoptive children differently than they would white children. And yet it seems that if this is the cause than though situation is not totally analogous (white biological mothers of mixed-race children), we should look toward post-World War II Germany to solve some of the problems America has in socializing its black youth [1]. Additionally, we might also investigate how white parents treat their adopted Asian children, because these youth display no ill effects of racism, but rather, often score higher on IQ tests than white children.

Also, check out godless' last comment over at Tacitus' thread....

[1] I do not by this suggest that we should institute a total racial state, liquidate our Jews, and prepare to deal with a massive invasion by the civilized nations that will destroy the heart & soul of our volk to purge our racist souls!

Skulls Offer First Glimpse of Early Human Faces. The short of it is that these skulls seem to indicate that anatomically modern humans existed in Africa before the climax of the Neandertals in Europe, pointing to the Out-Of-Africa thesis. The important point is that Chris Stringer, one of the earliest proponents of Out-Of-Africa, always asserted that the fossils supported him. Genetic methods and conclusions buttressed his position and eventually stole the spotlight from the paleoanthropologists like Stringer, but now the fossils are coming into line. This isn't conclusive, but I doubt that anything can ever really be definitive and final in this field....

Recently there has been discussion about the child tax credit which is part of the Bush administration's proposed tax cut.  Essentially it amounts to a $400/child tax deduction for families making less than $26K/year.  Both Republicans and Democrats are in favor of this credit, with the only disagreement being whether the credit should be temporary (Republicans) or permanent (Democrats).

Naturally both sides are falling over themselves emphasizing that they are in favor of the tax credit.  Nobody wants to appear to be opposed to a tax credit which helps poor families with children.  Well, I am opposed to it, and here's why.

This is a classic example of the "mutilated beggar effect".  Please let me digress momentarily to explain this.  In Cairo there exists a cottage industry which mutilates children to be used as beggars.  The more gruesome and pitiable the mutilations, the more the beggars will earn.  The disfigured children are placed on mats on street corners with a begging bowl and they ask for alms for the love of Allah.  The almsgiver is doing a good thing and a bad thing.  The good thing is paying for the mutilated child's next meal.  The bad thing is supporting a system which caused the child to be mutilated in the first place.

What is the analogy?  By giving poor families a per-child tax credit, we are doing a good thing and a bad thing.  The good thing is that we are paying for poor childrens' meals, clothing, etc.  The bad thing is supporting a system which financially encourages poor families to have more children than they can support themselves.

Families should not have more children than they are able to support.  If there were no social welfare, richer families would logically be larger families, since they could support more children.  In fact all through recorded human history and continuing to the present day poorer families tend to be larger.  In the past when people lived in agrarian communities this was an acceptable and appropriate state of affairs, since the children of a family were put to work farming and essentially "paid for themselves" via their work.  Now that most people live in urban communities this is no longer the case, and poor families can only be large if society supports them.

The logic is inescapable - the more society supports poor families' children, the more poor families are encouraged to have more children, and the more poor children there will be for society to support.  It is a loop with no exit.  Only by decreasing the financial incentives for having children will poor families adjust their numbers of children to be consistent with their ability to support them.  But this would take time, and political courage, because in the meantime poor children would be worse off.

There is zero chance that any politician will publicly take my point of view.  Why?  Because everyone would be horrified!  That would be - gasp! - like arguing against motherhood!  Yeah, so?

People often use "motherhood" as something nobody could be against.  As in, "arguing against child tax credits is like arguing against motherhood".  Let's think about this for a moment.  Why is "motherhood" something everyone can agree on?  Should every woman have as many children as she can?  Most women are physically capable of having about twenty children in their lives.  Should they do so?  Would society then just jump in and feed and clothe and educate all these children?  It doesn't really make sense.  In point of fact arguing against child tax credits is exactly like arguing against motherhood, or at least against irresponsible motherhood, and this is a good thing.

Perhaps you agree with this logic, but what can be done?  If no politician is willing to oppose motherhood (imagine the outcry), then are we doomed to an ever-increasing subsidy for poor families' children?  Already it is the case that in the U.S. a teenager with no marketable skills is financially better off having a child and going on welfare than she is working a minimum wage job.  Furthermore, if she marries the kid's father, she'll get less welfare.  Think about that for a moment, and then consider that 69% of all U.S. inner-city kids are born to a single mother.  This isn't a mystery, is it?  We're paying unskilled women to have kids, and paying them to stay single, so that's what they do.  It is just water flowing downhill.

I realize this can't all be reversed overnight.  Any change in these incentives would have to be phased in gradually over many years to avoid penalizing people (and their kids) for following the incentives.  But at least we can start by not making things worse.  Why use a tax cut designed to stimulate the economy as an excuse to increase the incentive for poor women to have children?

Let's go back to the child tax credit.  It was always part of the Bush plan, but pressure from Democrats has expanded it.  As Tom DeLay (R) put it, "To me, it's a little difficult to give tax relief to people who don't pay income taxes.  It's a spending program."  And the spending is a subsidy for having children.  The other point of view comes from Artur Davis (R), "People who are making between $10,000 and $20,000 can't throw a fund-raiser, don't have large teams of lobbyists, but they're people doing hard work for their country.  We ought to be valuing their contributions, not ignoring them."  Sure, let's value their contributions, but let's not pay them to have kids they can't afford.

Most mammals are hairy beasts. Short article on what we and naked mole rats are up to; Gene/culture evolution seems an interesting idea.
Also, this NewScientist anthology loosely grouped on human nature, including Dennett on free will.

I mentioned in a previous post that Sewall Wright’s ‘Shifting Balance’ theory of evolution had recently been criticised. It is only fair to add that it has also been defended. Key references are:

The original critique
J. Coyne, N. Barton and M. Turelli: A critique of Sewall Wright’s Shifting Balance theory of evolution. Evolution, vol. 51, 1997, pp.643-671
Counter-critiques
M. Wade and C. Goodenough, Evolution, vol. 52, 1998, pp.1537-53
S. Peck, S. Ellmer and F. Gould, Evolution, vol. 52, 1998, 1834-39.
Reply to the counter-critiques
Coyne, Barton and Turelli, Evolution, vol. 54, 2000, pp. 306-17
Replies to the reply
M. Wade and C. Goodenough, Evolution, vol. 54, 2000, pp.317-24
S. Peck, S. Ellmer and F. Gould, Evolution, vol. 54, 2000, pp.324-27

No doubt this will rumble on.

To refresh memories about the Shifting Balance theory, Sewall Wright believed that evolution in large, randomly-mating populations would be slow and ineffective. The population would quickly evolve to an optimum equilibrium state (a peak in the ‘adaptive landscape’), but evolution would then stop, because natural selection could not cross the ‘valleys’ to other peaks. Since evolution clearly does take place, Wright proposed that the geographical substructure of populations was important. In small isolated sub-populations inbreeding and genetic drift could enable the sub-population to cross ‘valleys’ to new peaks of fitness despite adverse natural selection on the way. Successful new combinations of genes could then spread by migration or differential extinction of groups. The theory has been widely influential in American biology, notably on Ernst Mayr’s view of speciation, the Eldredge-Gould theory of punctuated equilibrium, and D.S. Wilson and Michael Wade’s theories of group selection.

On the other hand the Shifting Balance was never very popular among evolutionists in Britain. Haldane was sceptical, R. A. Fisher was hostile, and E. B. Ford reported empirical evidence against it. Fisher in particular denied that large populations would get stuck on peaks in the adaptive landscape, since in a large population there would always be numerous mutations arising to upset the equilibrium, and in any case environmental conditions (biotic and non-biotic) were constantly changing. The idea of a static ‘adaptive landscape’ was therefore misleading. Fisher also doubted whether sub-populations would remain isolated for long enough to diverge purely by genetic drift. The recent debate is largely about whether Fisher or Wright was closer to the truth.

I won’t (and can’t) answer that question, but I think the opposition between Fisher and Wright is sometimes misrepresented. Wright is represented as believing that species are divided into partly isolated sub-populations, while Fisher is represented as believing that an entire species is a single large randomly-mating population. If the disagreement is put in these terms, clearly Wright is right. But of course Fisher was well aware that species have a geographical structure, and that sub-populations are partially isolated from each other. Where he dissented from Wright was in doubting that the isolation was usually strict enough, or lasting enough, to be as important as Wright claimed. His objection is expressed in the second edition of his Genetical Theory of Natural Selection:

“The circumstance that smaller numbers, even less than 100, are sometimes found to reproduce themselves locally, does not, as has been supposed, add to the frequency of random extinction [of genes], or to the importance of the so-called ‘genetic drift’. For this, perfect isolation is required over a number of generations equally numerous with the population isolated. Even if perfect isolation could be postulated, which is always questionable, it is still improbable that the small isolated population would not ordinarily die out altogether before a period of evolutionary significance could elapse, or that it would not later be absorbed in other populations with a different genetic constitution” (Dover edition, p.10).

The underlying problem with the Shifting Balance is that populations will not diverge by genetic drift if there is, on average, more than one migrant between them per generation, regardless of the size of the populations. (The last point may be counter-intuitive, but is well-established. The effectiveness of genetic drift is inversely proportional to the size of the population, so that with larger populations a proportionately lower migration rate is needed to prevent them drifting apart. Of course, none of this applies to asexual species, mitochondria, or Y chromosomes.) Fisher considered this degree of isolation unlikely in the absence of major geographical barriers. Oddly, neither Fisher nor Wright seems to have mentioned in this context that most species have behavioural and/or morphological adaptations for dispersal at some stage in their life-cycle. Among humans, exogamous marriage rules, or capture of females from other tribes, would have the same effect.

DAVID BURBRIDGE