The arguments in the group selection debate at The Edge, as kicked off by Steven Pinker, contain some useful descriptions on what is meant by multilevel selection in a modern sense and how this varies from older formulations of group selection. Some of this is worth drawing out.

The old story of group selection might run as follows. There are two types of people – altruists and egoists. Altruists are willing to incur individual costs for the benefit of the group, while egoists shirk this responsibility for their own benefit. As a result, egoists have higher fitness than altruists within groups, while groups with higher proportions of altruists do better than groups with relatively more egoists. If altruistic groups have a large enough advantage over groups with more selfish individuals, and as a result grow faster and bud off new groups, it may be possible for altruists to increase in overall prevalence even though egoists have an advantage within groups.

Maynard Smith’s haystack model was one of the many early critiques of this picture. Maynard Smith argued that the conditions required for the evolution of an altruistic trait (in his haystack model, timidity compared to the dominant aggressive trait), were so limited that they were unlikely to be satisfied. These conditions included a limited level of migration between groups and large differences in relative group fitness. Group selection theory also suffered from criticism of a lack of preciseness about how the selection at various levels should be weighted.

Since then, multilevel selection theory has tightened a few of those issues up. First, from David Queller:

Modern group selection theory is as mathematically rigorous as individual selection or inclusive fitness theory. … They simply divide up fitness in slightly different ways – inclusive fitness into effects on self versus others, and multilevel selection into between-group and within-group parts – and a simple partition of fitness should not alter predictions. Inclusive fitness became popular, despite the head start enjoyed by multilevel selection thinking, because it successfully weighted the relative importance of its two fitness components, using genetic relatedness. Without a similar set of weights, group selection advantages could not be accurately judged, and their strength and importance was often overemphasized. … However, modern multilevel selection theory does have such weights, the between-group and within-group genetic variances, whose ratio happens to be relatedness of the actor to its groupmates (including itself). Once the proper weights are accounted for, the two approaches give essentially identical results.

As well as tightening up the mathematics, the definition of group was also tweaked. Rather than talking about competition between distinct populations, multilevel selection looks at competition of all levels of organisation, with groups formed within populations at various stages of the life-cycle. Pinker writes:

In most models of the new group selection, a group is defined as any subset of interacting individuals, that is, as organisms which interact with one another more intensely than they interact with organisms selected from the population at random. Two sisters who help each other, for example, or a pair of friends who trade favors, are dubbed “a group”.

It is this new grouping arrangement that is partitioned and weighted:

… Once a “group” is defined as a subset of interacting individuals, the variance in the fitness of individuals can be partitioned into two statistical components: how fit the individual is with respect to his groupmates, and how fit his group is with respect to other groups. … Examples include huddling for warmth, mobbing a predator, and Tooby’s example of pooling resources to get higher expected returns in a risky investment. In such cases one can separate the benefits that accrue to the entire group (including me) and whatever benefits or costs are assumed by me but no one else in the group.

This is not to say that everyone is on board with this statement that the two approaches are mathematically equivalent. However, the mathematical equivalence and greater flexibility about what constitutes a group provide group selection advocates an alternative argument about why it is useful.

Unfortunately, the new approach is often used as a trojan horse for the old group selection approach, particularly in popular discussions of human evolution. The responses to Pinker contain various varieties of this.

Pinker also makes some interesting points about the costs of the new approach. First, the flexibility in the definition of groups is multi-level selection’s weakness.

If the two theories really are equivalent, then any advantage of group selection (in this new sense) would have to come from the models’ being more convenient, elegant, simple, transparent, explanatory, or mathematically tractable. Yet by stretching the meaning of “group” beyond its ordinary sense, that’s just what they fail to be. …

[A] mathematical model that submerges the psychological forces that keep different “groups” together (such as genetic relatedness or mutual sensitivity to altruism), and requires theorists to dig them out from under the equations, is hardly a perspicuous way to analyze sociality (as Coyne points out). In gene-selectionist theories, the theoretical constructs that power the models turn out to be fantastically psychologically important, including sensitivity to kinship, scrutiny of individuals, moralistic emotions elicited by benefits conferred or withheld, and the psychological differentiation of relationships into discrete models corresponding to mutualism, kinship, reciprocity, and dominance.

Pinker also picks up what I consider to be the major reason multilevel selection has not been as broadly accepted as its proponents hope:

Mathematical biologists such as Alan Grafen, Stuart West, Ashleigh Griffin, and Andy Gardner have criticized this formulation because it obfuscates the fact that individuals are still maximizing their genetic fitness: “The fundamental point is that the spread of a gene is determined by its ‘fitness relative to others in the breeding population, and not to others with which it happens to interact.’ … Natural selection selects for a gene if it causes a behavior that leads to that gene increasing in frequency in the population, not some other arbitrarily defined scale such as social partners.”

This point can be drawn out through examining some of the similarities between the cooperation identified in a multilevel selection framework and the way economists look at economic exchange. I will offer some more thoughts on this in my next post on group selection.

*As an aside, I am deliberately avoiding the cultural group selection issue for the moment.

Steven Pinker’s essay on group selection (my initial post on it here) has now attracted a raft of interesting responses that are well worth reading. While it is hard to stitch together and reconcile the various arguments, in sum they confirm one part of Pinker’s argument. In his essay, Pinker wrote:

The first big problem with group selection is that the term itself sows so much confusion. People invoke it to refer to many distinct phenomena, so casual users may literally not know what they are talking about. I have seen “group selection” used as a loose synonym for the evolution of organisms that live in groups, and for any competition among groups, such as human warfare. Sometimes the term is needlessly used to refer to an individual trait that happens to be shared by the members of a group; as the evolutionary biologist George Williams noted,”a fleet herd of deer” is really just a herd of fleet deer. And sometimes the term is used as a way of redescribing the conventional gene-level theory of natural selection in different words: subsets of genetically related or reciprocally cooperating individuals are dubbed “groups,” and changes in the frequencies of their genes over time is dubbed “group selection.”

In the responses, Herb Gintis talks of gene-culture evolution. Jonathan Haidt suggests that to see group selected traits, we should look at groupishness in inter-group competition. Peter Richerson talks of cultural group selection and traits such as language. David Sloan Wilson and David Queller look at the technical alignment between inclusive fitness and multi-level selection, which is a biologically focused approach. Across the responses, most of Pinker’s varieties of group selection are covered, and many responses cannot be reconciled with the others as they are talking about different ideas.

To resolve this confusion, there needs to be greater differentiation of the various phenomena that people are trying to describe. A starting point would be removing the label of “group selection” from some of them. Daniel Dennett picks up on this point:

Pete Richerson’s comment  articulates the details well, but muddies the water by speaking of cultural group selection. There are reasons for calling these phenomena a variety of group selection, reasons ably recounted by Boyd and Richerson in many publications, but better reasons—in my opinion—for avoiding the label, precisely because it seems to give support to the vague and misguided ideas of group selection that Pinker exposes so effectively. These phenomena consist in the evolution by natural selection (both cultural and genetic) of what might be called groupishness adaptations, dispositions (or traditions) of cooperation and the punishment of defectors, and the like, but not by a process of differential reproduction of groups. What differentially reproduce in these phenomena are groupishness memes, not groups. The establishment of these memes may then enable the genetic evolution of enhancements in hosts—like the lactose toleration that evolved in response to the culturally spread tradition of dairying. This is no more group selection than the differential reproduction of the flora in our guts is group selection.

Personally, I would accept some of these phenomena being called group selection if they always had the prefix of “cultural” attached. At that point, some biologists will drop their instinctive opposition and the debates will be able to focus on the question of whether cultural group selection was important in the evolution of the trait of interest or is a useful framework for analysing it. As I argued in my initial response to Pinker’s piece, cultural group selection avoids some of the issues associated with “biological” group selection. Peter Richerson also makes this point:

Natural selection on large scale patterns of cultural variation is plausible because the cultural variation between neighboring groups that might compete is typically much larger than the genetic variation between the same groups. The reasons are not hard to see; all human groups are more or less open to immigration. Groups intermarry and intermarriage is a very effective conduit for genes. This is less true of culture. Because culture evolves more rapidly than genes, groups will continue to differ despite migration. A large body of social psychology research has characterized the active mechanisms that damp down variation within groups and protect between group variation from the effects of migration. Human social groups are psychologically very salient entities as Pinker acknowledges.

Bryan Caplan points out a paper by  Henrik Cronqvist and Stephan Siegel on the genetic and parental influences on savings behaviour. The first part of the abstract reads:

Analyzing identical and fraternal twins matched with data on their savings propensities, we find that genetic variation explains about 33 percent of the variation in savings behavior across individuals. Parenting effects on savings behavior are strong for those in their twenties but decay to zero by middle age, i.e., parents do not have a lifelong non-genetic impact on their children’s savings. The family environment when growing up and an individual’s socioeconomic status later in life moderate genetic effects, so that more supportive environments result in a stronger genetic expression of savings behavior.

There are no surprises in these results. The proportion of the variance in savings explained by genetic variation is typical of that for many other social traits. And once opportunity is equalised, genetics becomes more important.

The evidence that parental influence fades out for older subjects and disappears by age 45, compared to the relatively constant genetic effects, is interesting. The break down of effects by age is not a regular feature of studies such as these (it comes at the cost of sample size). The authors write:

Our interpretation of this evidence is that social transmission from parents to their children affects children’s savings behavior early on in life, but unlike genetic effects, parenting does not have a lifelong impact on an individual’s savings behavior. These results are broadly consistent with research in behavioral genetics which has found a significant effect of the common family environment in early ages on, e.g., personality, but also shown that such effects approach zero in adulthood

It is a pity that savings behaviour is only exhibited without significant constraints in adulthood, as if we could also get data for the first twenty years of life, we might also see the genetic influence increase as happens for IQ.

In the conclusion, the authors link the observed behaviour to time preference and self-control. Those with lower savings rates are probably also suffering the consequences of impatience and poor self-control in many aspects of their lives.

One explanation for why savings behavior is genetic appears to be that an individual’s time preferences are partly genetic. Our evidence of a significant positive genetic correlation between an individual’s savings and income growth supports such an explanation. Some individuals are born to be more patient, and this affects these individuals’ savings behavior, as well as other outcomes, e.g., the choice of income process. Moreover, the negative and significant genetic correlation between savings rate and both smoking and body weight suggests that behavioral factors such as lack of self-control may also affects savings behavior. For example, to the extent that a high BMI and obesity may be interpreted as an expression of lack of self-control, we conclude that lack of savings correlates with lack of self-control, and this correlation is mainly found to be genetic.

For those looking for more on the subject, there is a lecture by Cronvqist on this paper on Vimeo:

[vimeo http://vimeo.com/16490797]

 

As an end note, in the closing of Caplan’s post, he notes that there is still much variation that is not explained by either parental effects or genes. Caplan falls back on his old free will argument, but there is a lot to be said for noise. This is a subject I hope to come back to in the near future.

At the end of Moav and Neeman’s paper on conspicuous consumption and poverty traps, about which I posted yesterday, the authors suggest an experiment:

It is well known that the rich spend a lot more on charitable contributions than the poor. There are at least three different explanations for this behaviour: charitable contribution is a luxury good, there is stronger social pressure on the rich to contribute more to society and our suggestion that charitable contributions provide a signal about unobserved income (‘success’). Consider the effect of the revelation of information about individuals’ incomes. Such a revelation should have no effect on charitable contributions if they are mostly a luxury good. It should lead to a rise in charitable contributions if they are mostly due to social pressure on the rich to contribute to society and it should lead to a decrease in charitable contributions if they are mostly about signalling. It ought to be possible to examine empiricaly the effect of such a revelation of information on charitable giving.

I like the idea, but how could this experiment practically be implemented? Their suggestion reminded me of the closing paragraph of an article by Griskevicius and colleagues, in which they reported the results of experiments that tested the desire to engage in benevolent activity in response to priming with mating motives. They write:

[M]edia mogul Ted Turner once bemoaned the influence of the Forbes 400 list of richest Americans, pointing out that it discouraged the wealthy from giving away their money for fear of slipping down in the rankings (Plotz, 2006). He suggested instead that a public ranking of top philanthropists could inspire the wealthy to compete in a more beneficial way—in essence, by shifting the signaling arena from conspicuous consumption to blatant benevolence. Perhaps it was not a coincidence that just such a list—the Slate 60—was established the same year that Ted Turner pledged $1 billion to humanitarian relief. When asked about the reaction of his then-wife Jane Fonda to this donation, Turner fondly reminisced, “It brought tears to her eyes . . . . She said, ‘I’m so proud to be married to you’ ”

The need to engage is conspicuous consumption drops away if your wealth is published each year.

Poverty is no barrier to conspicuous consumption. As Banerjee and Duflo wrote in Poor Economics:

One hidden assumption in our description of the poverty trap is that the poor eat as much as they can. …

Yet, this is not what we see. Most people living with less than 99 cents a day do not seem to act as if they are starving. If they were, surely they would put every available penny into buying more calories. But they do not. In our eighteen-country data set on the lives of the poor, food represents from 36 to 79 percent of consumption among the rural extremely poor, and 53 to 74 percent among their urban counterparts.

It is not because all the rest is spent on other necessities: In Udaipur, for example, we find that the typical poor household could spend up to 30 percent more on food than it actually does if it completely cut expenditures on alcohol, tobacco, and festivals.The poor seem to have many choices, and they don’t elect to spend as much as they can on food.

In a paper published earlier this year, Moav and Neeman proposed an explanation for the relatively high levels of consumption on goods other than food in poor societies. They suggested that some of this consumption is conspicuous consumption, which is driven by the difficulty in signalling status and wealth where it is not recognisable through professional titles or other markers:

[W]we suggest that those with high human capital have a recognisable ability (professional titles, degree certificates etc.) and relatively little need to signal success, whereas those without certified accomplishments, such as the poor and the ‘newly rich’, have a relatively stronger motivation to impress via conspicuous consumption. As a result, the fraction of income allocated to conspicuous consumption can decline, on average, with the level of human capital, resulting in a larger share of income allocated to savings and investment in education.

Conspicuous consumption is only useful to the extent that someone is signalling a quality that cannot otherwise be determined. If the quality is observable, there is no need for the signal.

To explore this idea, Moav and Neeman developed a model in which a person’s knowledge, skills and experience (what is called human capital) is observable to others. However, a person’s income is not directly observable, although it is imperfectly correlated with their human capital. To attempt to signal the unobservable variation in income, a person can engage in conspicuous consumption.

In each model generation, an adult must divide their resources between normal consumption, conspicuous consumption and a bequest to their children, which determines that child’s level of human capital. The adult gets utility from the three options.

Moav and Neeman showed that depending on the relationship between human capital and income, it was possible for the share of conspicuous consumption as a proportion of income to be decreasing with income. That is, the poor would engage in relatively more conspicuous consumption as a share of their income than the rich. The condition for this to occur is that human capital acts as a buffer to negative income shocks, meaning that variation in income is likely to be relatively less as human capital rises.

When this is put into a dynamic context over generations, this situation can turn into a poverty trap. Adults with low human capital tend to invest more in conspicuous consumption, which then prevents investment in the human capital of their children. As a result, the human capital of that dynasty remains low and they stay in a poverty trap. Those with high human capital, however, invest relatively less of their income in conspicuous consumption, which leaves resources for increasing the human capital of their children. As the share of conspicuous consumption as a portion of someone’s income declines with increasing income, the high human capital dynasty ends up in a virtuous circle of increasing human capital and wealth.

I am not convinced of the conclusion of conspicuous consumption leading to poverty traps, as human capital is not purely a function of parental investment. Further, to the extent that conspicuous consumption is a signal of resources and leads to differential reproductive success, the people in the successive generations will only be a subset of the dynasties that were initially in existence. However, as the authors note, there is potential to test this idea by exploring conspicuous consumption across societies and to see whether it varies with variation in the transparency of income.

I would have like to have seen the model placed in an evolutionary setting, particularly given Moav’s background in the area (Moav is one of the authors of the seminal Natural Selection and the Origin of Economic Growth). It is possible to frame the model in evolutionary terms with little need for any model modification. This would answer questions such as why the people prefer to conspicuous consumption, and what is the fitness benefit that allows it to continue to occur? Evolutionary dynamics may be beyond the length of time for which Moav and Neeman seek to explore, but the evolutionary foundations of people’s actions would give robustness to the preference to conspicuously consume.

Steve Hsu has pointed out an interesting old interview with Noam Chomsky. Hsu highlights Chomsky’s views on the limits of human intelligence.

It was possible in the late nineteenth century for an intelligent person of much leisure and wealth to be about as much at home as he wanted to be in the arts and sciences. But forty years later that goal had become hopeless. …

I think it has happened in physics and mathematics, for example. There’s this idea, which goes back to the French mathematicians known collectively as Bourbaki, that the development of mathematics was originally the exploration of everyday intuitions of space and number. That is probably somewhat true through the end of the nineteenth century. But I don’t think it’s true now. As for physics, in talking to students at MIT, I notice that many of the very brightest ones, who would have gone into physics twenty years ago, are now going into biology. I think part of the reason for this shift is that there are discoveries to be made in biology that are within the range of an intelligent human being. This may not be true in other areas.

While I am not convinced that Chomsky’s prediction of bright students going into biology played out (didn’t they all go into finance?), it is an interesting question. Is biology inherently more accessible?

Contrast the current group selection debate, such as that being played out at The Edge following Steven Pinker’s essay critiquing group selection, with the discussion of the discovery of the Higgs boson. The group selection debate has a range of participants from academic biologists to popular science writers to bloggers. It takes little investment to have an opinion. In contrast, for all but a few physicists, we are passive receivers of information about the Higgs boson.

However, the group selection debate is not necessarily a perfect example of an easily accessible topic. Reading through the responses to Pinker’s essay, it is clear that many of the responders do not have a common understanding of what group selection is. When the statement is made that the inclusive fitness and multi-level selection approaches can be shown to be mathematically equivalent representations, most people do not understand how or why that might be the case. And if we take one of the triggers of the recent escalation in debate, Nowak, Tarnita and Wilson’s Nature paper attacking kin selection, the majority of the debate participants do not fully understand the mathematics that underpins it, including one of the paper’s authors himself. While physics may have progressed to a level such that it is less accessible than biology, some of the accessibility of biology is illusory.

As an aside, how quickly would a debate about the Higgs boson would emerge in the blogosphere if its existence had a bearing on politics and whether government should be large or small?

Sarah Hill has posted at Scientific American on a new paper (pdf) that she (and colleagues) has written on the lipstick effect. The lipstick effect is a phenomena where sales of beauty products increase in times of recession, in contrast to the reduction in purchases for most other goods. The authors suggest that this reflects the desire of women to reproduce more quickly, and competition between women for access to the relatively scarcer resource-rich men. Part of the abstract reads:

Findings revealed that recessionary cues—whether naturally occurring or experimentally primed—decreased desire for most products (e.g., electronics, household items). However, these cues consistently increased women’s desire for products that increase attractiveness to mates—the first experimental demonstration of the lipstick effect. Additional studies show that this effect is driven by women’s desire to attract mates with resources and depends on the perceived mate attraction function served by these products.

The most interesting element of this paper is the argument that the lipstick effect is not driven solely by resource needs. One of the five studies reported in the paper directly addressed this point:

The second goal of Study 4 was to rule out an alternative hypothesis derived from social roles theory (see Eagly & Wood, 1999)—specifically, that the lipstick effect may reflect women’s greater resource need in a recession. On this view, because resources tend to be controlled by men, economic recessions should prompt women to attract wealthy mates specifically as a means to obtaining these rarified resources. In contrast, our evolutionary model predicts that economic resource scarcity should lead women to invest more effort in mate attraction effort because such conditions heighten reproductive goal immediacy and signal diminished access to high-quality mates, both of which prompt greater mate attraction efforts. …

From a social roles perspective, which would predict that the lipstick effect reflects women’s increased resource needs in a recession, women’s own resource access (e.g., her socioeconomic status [SES]) should be the driver of the lipstick effect. That is, the effect should be driven primarily by lower SES women, whose resource need is greatest. In contrast, our evolutionary model predicts that uncertain economic climates should lead women to heighten mate attraction effort—and to do so irrespective of their own resource need.

Study 4 supported the authors’ hypothesis:

[C]onsistent with our model based on theories in evolutionary psychology, a robust lipstick effect was found in women across levels of SES. … Furthermore, that each of our studies revealed evidence of a robust lipstick effect, despite the fact that many of the women in our sample came from backgrounds implying low resource need, indicates additional evidence that the lipstick effect does not emerge exclusively in response to objective resource need. These results provide  support for the idea that social roles, by themselves, are unlikely to provide a complete explanation for the lipstick effect.

I would be interested in examining this from a slightly different angle, focusing on the uncertainty associated with recessions and not the low resource availability that accompanies them. If we think of an r/K selection framework, unstable environments tend to result in strategies of rapid reproduction when possible, whereas stable but resource constrained environments lead to greater investment in quality of offspring. The lipstick effect is a response to the uncertainty. If these experiments were run with women with children who must face a quality-quality trade-off, and not the young, college attending women used in the experiments in this paper, we could  examine this point further.

An article by Bentley and colleagues published in PNAS last month points to some very early evidence of persistent inequality. The study headline is the uncovering of the earliest (statistically significant) evidence of status and wealth differences among the first farmers of Neolithic Europe and the existence of a patrilocal kinship system. However, the analysis also suggests that the healthiest farmers when young were also the richest when buried. Early advantage persisted until death.

It takes some reading between the lines in the PNAS article to see this result, but a Guardian piece containing interviews with the study authors is more direct:

Some of the male skeletons were buried with stone adzes – cutting and chopping tools – which were often beautifully polished and made from carefully selected stone, and so were probably also symbols of status and wealth. An analysis of the strontium isotopes in their tooth enamel showed these individuals had lived on food grown in “loess”, the most fertile and productive soil.

Because strontium markers are laid down in tooth enamel in childhood, it seems they hadn’t earned but inherited this richer diet, and the fact that they were buried with the adzes suggests that they died as they had lived: privileged to the end.

“This strongly suggests that access to the best soils was being passed on between generations,” Bickle said. “Thus, while I think it’s not news that status differences and subsistence specialisms date to the Neolithic, this is perhaps the first time we’ve been able to show that inheritance was a large part of this.”

The usual question arises at this point – what mix of genetic endowments, productivity effects related to upbringing (such as the poor health) and resource transfers delivered this result?

Enrico Spolaore and Romain Wacziarg have put out a nice review article on long-term economic growth and the intergenerational transmission of development. Below are some of the more interesting parts.

They note two important papers (which I intend to write more detailed posts about at some stage) by Louis Putterman and David Weil, and by Comin, Easterly and Gong. They write:

[Putterman and Weil] examine explicitly whether it is the historical legacy of geographic locations or the historical legacy of the populations currently inhabiting these locations that matters more for contemporary outcomes. …

Putterman and Weil’s results strongly suggest that the ultimate drivers of development cannot be fully disembodied from characteristics of human populations. When migrating to the New World, populations brought with them traits that carried the seeds of their economic performance. This stands in contrast to views emphasizing the direct effects of geography or the direct effects of institutions, for both of these characteristics could, in principle, operate irrespective of the population to which they apply. A population’s long familiarity with certain types of institutions, human capital, norms of behavior or more broadly culture seems important to account for comparative development. …

The deep historical roots of development are at the center of Comin, Easterly and Gong (2010). They consider the adoption rates of various basic technologies in 1000 BC, 1 AD, and 1500 AD. in a cross-section of countries defined by their current boundaries. They find that technology adoption in 1500, but also as far back as 1000 BC, is a significant predictor of income per capita and technology adoption today.

Spolaore and Wacziarg also note Easterly and Levine’s paper on the link between European settlement and economic growth (a later version of which I mentioned last week).

Spolaore and Wacziarg were the authors of The Diffusion of Development, about which I have previously posted. In that paper, they proposed that genetic distance acts as a barrier to technology transfer, so that when one population becomes more technologically advanced, even if through luck, the barrier to transfer results in differences in economic development. In this new paper, they explain the mechanism as follows:

[T]he mechanism need not be a direct effect of those traits (whether culturally or genetically transmitted) on income and productivity. Rather, divergence in human traits, habits, norms, etc. have created barriers to communication and imitation across societies. While it is possible that intergenerationally transmitted traits have direct effects on productivity and economic performance (for example, if some parents transmit a stronger work ethic to their children), another possibility is that human traits also act to hinder development through a barrier effect: more closely related societies are more likely to learn from each other and adopt each other’s innovations. It is easier for someone to learn from a sibling than from a cousin, and easier to learn from a cousin than from a stranger. Populations that share more recent common ancestors have had less time to diverge in a wide range of traits and characteristics – many of them cultural rather than biological – that are transmitted from a generation to the next with variation. Similarity in such traits facilitates communication and learning, and hence the diffusion and adaptation of complex technological and institutional innovations.

Spolaore and Wacziarg also mention the other (few) core papers or books in the field of biology and economic growth – by Gregory Clark, Galor and Moav and Ashraf and Galor. It is still a short list.

One of their conclusions for this review is that greater focus should be on populations and not locations:

The importance of controlling for populations’ ancestry highlights the second message from this literature: long-term persistence holds at the level of populations rather than locations. A focus on populations rather than locations helps us understand both persistence and reversal of fortune, and sheds light on the spread of economic development. The need to adjust for population ancestry is at the core of Putterman and Weil’s (2010) contribution, showing that current economic development is correlated with historical characteristics of a population’s ancestors, including ancestors’ years of experience with agriculture, going back, again, to the Neolithic transition. The overall message from Comin, Easterly and Gong (2010), Putterman and Weil (2010) and several other contributions covered in this article is that long-term historical factors predict current income per capita, and that these factors become much more important when considering the history of populations rather than locations.

The article also has some interesting thoughts on gene-culture coevolution (is there anything else?) and is generally worth the read.

I was surprised at the easy run that group selection has recently had in social science circles, so I am pleased to see that Steven Pinker has waded into the fray with an essay in Edge. Pinker’s whole essay is worth a read, but there were a couple of parts of it that I particularly liked.

The first was Pinker’s highlighting that when many social scientists talk of group selection, they are talking of cultural group selection. Pinker writes:

[M]ost of the groupwide traits that group selectionists try to explain are cultural rather than genetic. The trait does not arise from some gene whose effects propagate upward to affect the group as a whole, such as a genetic tendency of individuals to disperse which leads the group to have a widespread geographic distribution, or an ability of individuals to withstand stressful environments which leads the species to survive mass extinction events. Instead, they are traits that are propagated culturally, such as religious beliefs, social norms, and forms of political organization. Modern group selectionists are often explicit that it is cultural traits they are talking about, or even that they are agnostic about whether the traits they are referring to are genetic or cultural.

What all this means is that so-called group selection, as it is invoked by many of its advocates, is not a precise implementation of the theory of natural selection, as it is, say, in genetic algorithms or artificial life simulations.

Cultural group selection is less prone than “biological group selection” to the criticism that migration and gene transfer between groups prevents genetic differentiation from emerging. It may be possible to argue that when someone joins the group, they absorb the culture or that it is the culture of the whole population that matters. However, you then run into Pinker’s broader question of whether the concept of cultural group selection adds anything to “history”.

Another interesting point Pinker makes is that apparently altruistic behaviour may be more a case of manipulation than evidence of a generally selfless inclinations.

What we don’t expect to see is the evolution of an innate tendency among individuals to predictably sacrifice their expected interests for the interests of the group—to cheerfully volunteer to serve as a galley slave, a human shield, or cannon fodder. … What could evolve, instead, is a tendency to manipulate others to become suicide attackers, and more generally, to promulgate norms of morality and self-sacrifice that one intends to apply in full force to everyone in the group but oneself. If one is the unlucky victim of such manipulation or coercion by others, there’s no need to call it altruism and search for an evolutionary explanation, any more than we need to explain the “altruism” of a prey animal who benefits a predator by blundering into its sights.

This manipulation extends into the manner in which we treat non-kin as kin.

The cognitive twist is that the recognition of kin among humans depends on environmental cues that other humans can manipulate. Thus people are also altruistic toward their adoptive relatives, and toward a variety of fictive kin such as brothers in arms, fraternities and sororities, occupational and religious brotherhoods, crime families, fatherlands, and mother countries. These faux-families may be created by metaphors, simulacra of family experiences, myths of common descent or common flesh, and other illusions of kinship.

Pinker makes some other good points, but one element I alluded to above is missing from Pinker’s argument – the critique of group selection on the basis of migration and gene flow between groups. While advocates of group selection in humans often spend much effort on showing how human groups experienced regular conflicts and wars, little is focused on the likely transfer of people between groups through capturing women from the losers in war or through exogamy. It takes little inter-group migration to prevent genetic differentiation between groups. If you were to ask what it would take for me to believe that group selection was a significant force in shaping human traits, it is on this point that you would need to change my mind.

*I make some comments on the responses to Pinker in this later post.