Saturday, March 30, 2013

Do you even read?

Since 2011 my colleagues and I have been thinking about cultural tightness and looseness and how it might pertain to the religious congregations we engage with as part of the Binghamton Religion and Spirituality Project.  For those unfamiliar with these terms, tightness refers to the strength of norms and sanctions within a particular group.  Groups with strong norms enforced by sanctions are said to be "tight" while those with weak norms or with a high tolerance for deviant behavior are said to be "loose."  In principle, it is possible to rank communities on a continuum between "loose" and "tight" and to do so for groups as small as local congregations or as large as nations.

We've found this to be a particularly interesting conception for several reasons.  First, it resonates with our observations in the field.  Some churches we visit seem to emphasize the individual and his or her personal spiritual journey, valuing diverse spiritual expressions and individual autonomy.  Other churches, by contrast, place much more emphasis on shared values and group conformity, with highly constrained beliefs, behaviors and practices.  Second, the relative tightness of groups correlates with environmental factors.  In particular, it correlates with existential insecurity such that communities that face (or believe they face) greater threat tend to be tighter than communities that are (or perceive themselves to be) more secure.  This fits well with our ecosystems approach to studying religious communities. Finally, tightness and looseness are, at their roots, about tolerance for variation, and variation, in turn, is the essential building block upon which natural selection can work its wonders.  As such, the tight/loose axis of cultural variation fits more directly into an evolutionary narrative than virtually any others that are frequently discussed and it does so in a way that is readily amenable to study from a multi-level selection perspective.

The classification scheme is not without its problems, of course.  For one, it's a bit uncomfortable approaching churches about how tight or loose they might be.  That just brings a whole list of unfortunate connotations to the table that inflect in particularly unfortunate ways in religious communities.  But these are the terms we're kind of stuck with, at least at an academic level.  As a number of papers point out, these were terms laid down by an anthropologist by the name of Pertti Pelto in 1968 in his seminal paper entitled "The Differences Between 'Tight' and 'Loose' Societies."  For instance, Gelfand et al (2006) state that:

"Pelto (1968), an anthropologist, was the first to theorize on tightness–looseness, arguing that traditional societies varied in their expression of and adherence to social norms." p. 1226

Similarly, Gelfand, in a 2012 paper, explains:

"The idea that societies vary on tightness-looseness dates back to early anthropological work by Pertti J. Pelto."  p. 420

So we have Pelto to blame.  Except, of course, that we don't.  Pelto was not the first person to use these terms.  In fact, his 1968 paper was not in any way about describing some new cultural syndrome that no one had articulated before.  Rather, Pelto was complaining about the lack of any objective standards in the anthropology of his time by which to evaluate tightness or looseness.  So how did Pelto become the father of this construct?  I'm not sure, but I suspect it's because his paper is one of the most cited by researchers in the field.  Almost by default, if you're going to introduce the concept of cultural tightness in a paper, you're probably going to cite Pelto's 1968 paper.  The fact that he is now being credited, though, as the founder of these concepts makes me wonder how many people actually bother to read the article they're citing.

Now, I understand that it's not possible or desirable to trace every scientific concept back to its very beginnings.  Moreover, I understand how tedious it can be to work through relatively archaic literature.  However, Pelto's 1968 article is only 4 pages long and it's not like you have to dig too deeply to discover that he was not the one to coin these terms.  In fact, you don't have to read beyond the very first sentence!

"For about 30 years, anthropologists have been classifying human societies as 'tight' or 'loose.'" p. 37

Okay, I'm just being pedantic I know.  In the grand scheme of things this is not a terribly important bit of history that scholars need to get right.  Moreover, it doesn't even make a difference in how firmly entrenched these terms are.  If anything, a more accurate history just shows that these terms have an even deeper history that make them that much less amenable to change.  Nevertheless, I do think it represents a wider problem in science that seems to be getting worse as the information age proceeds at an ever increasing pace.  People either don't have the time or just don't see the need to read the sources they're citing.  Instead, they seem just to skim abstracts or they get a sense from what others have said rather than going to the original.  How many people, for instance, could tell you that Hardin's famous articulation of the "Tragedy of the Commons" was in support of a rather radical call for draconian birth control mandates?  Similarly, how many people know that Darwin did not, in fact, have an epiphany about the mechanisms of natural selection while visiting the Galapagos Islands?

Maybe none of this really matters.  Nevertheless, I hold on to a quaint belief that the text that falls between the introduction and conclusions sections of papers or chapters of books is doing more important work than simply taking up space.  If we dispense with it entirely, then we might as well go to Twitter as our primary means of publication.


Gelfand, M. J. (2012). "Culture's Constraints: International Differences in the Strength of Social Norms." Current Directions in Psychological Science 21(6): 420-424.

Gelfand, M. J., L. H. Nishii and J. L. Raver (2006). "On the Nature and Importance of Cultural Tightness–Looseness." Journal of Applied Psychology 91(6): 1225–1244.

Hardin, G. (1968). "The Tragedy of the Commons." Science 162: 1243-1248.

Pelto, P. J. (1968). "The difference between "tight" and "loose" societies." Transaction 5(5): 37·40.

Friday, February 22, 2013

What is an "evolutionary perspective?"

Proponents of evolutionary studies (EvoS) claim that an evolutionary perspective makes it possible to make sense of a broad range of different disciplines.  In fact, in more private moments I've heard claims that disciplines outside the hard sciences are primarily atheoretical and that the lack of a unifying framework has hindered their progress.  Instead, the thinking goes, these different scholarly traditions lumber along with each generation doing nothing more than finding clever ways of discrediting the generation before, with no lasting body of theoretical or empirical work to build from.

Naturally, EvoS advocates claim that evolution can save the day.  Taking an evolutionary perspective, they propose, makes it possible to unite vastly disparate scholarly traditions and to make sense of an otherwise chaotic intellectual landscape.  At first blush, this seems plausible, perhaps even compelling.  Or at least it does if you're trained in the life sciences where evolutionary theory does important work.  As Dobzhanzsky is so often quoted as saying, "Nothing in biology makes sense except in light of evolution," so how could taking an evolutionary perspective not shed light on all the other things that life has managed to create? 

Underneath all this enthusiasm, however, is one rather glaring problem.  Namely, what does it mean to take an evolutionary perspective?  For that matter, what is an evolutionary perspective in the first place?  In all the years I've been associated with EvoS I can’t recall anyone ever articulating exactly what they mean by this and I'm coming to find that rather deeply troubling and problematic.  Underneath it all is an implication that evolutionary theory is a single thing, a unified set of principles by which life can be understood.  With a bit of training in how to use the "evolutionary toolkit," the story goes, all of life's mysteries can be revealed and that holds as true for culture, economics, psychology, literature, etc. as it does for biology. 

As someone trained in evolution, though, I have to ask just what is this toolkit we’re all supposed to have?  Is it simply Darwin's recipe of mixing inheritance, variation and selection?  Is that the simple logic that scholars should rally around?  In biology, the answer would seem to be a rather resounding no and it has been since the Modern Synthesis.  At the very least, then, taking an evolutionary perspective should include things like Mendelian inheritance, mutation and population genetics.  However, we can’t stop there.  As the Extended Synthesis is demonstrating, no evolutionary toolkit would be complete without also including topics such as evo-devo, phenotypic plasticity, multilevel selection, epigenetics, niche construction, robustness and evolvability.  In seeking conscilience, though, we’re trying to explain human behavior, too, so what are we to make of culture?  Cultural evolution is an obvious answer, but this hardly represents a unified perspective.  While not necessary at odds with one another, gene culture coevolution is nevertheless a fundamentally different discipline than evolutionary psychology, which is itself hardly a single theoretical framework, and these both offer very different approaches, methodologies and preoccupations than human sociobiology, behavioral ecology and memetics.

As best I can tell, then, there is no single evolutionary perspective, no single evolutionary toolkit.  Rather, the study of evolution has led to a rather dizzying array of specialized disciplines, each asking different kinds of questions about different kinds of phenomena.  Sure, there are varying degrees of overlap between many of these fields.  However, I doubt that many specialists in, say, niche construction, would be so bold as to claim expertise in evolutionary psychology simply because both fields can trace lines of intellectual thought back to Darwin.  Yet I have heard similarly bold claims, both publicly and in private, about what EvoS can bring to nearly every intellectual tradition imaginable.  If "applying an evolutionary perspective" is nothing more than arguing by analogy from biological principles, then to a limited extent I suppose this is true.  However, I can hardly blame those who have been trained in rich intellectual traditions with deep histories outside the Darwinian aegis if they find the application of biological analogies less than compelling or far from illuminating.

All that said, I remain cautiously enthusiastic about EvoS.  As a program it does have the capability to facilitate dialog between disciplines and to foster unique interdisciplinary research programs.  However, until we’re able to articulate a consensus about what this "evolutionary perspective" is that we all seem to take for granted, the ability of EvoS to bring about any kind of conscilience will remain a distant and rather fanciful dream.

Monday, February 18, 2013

Religion and Parasitic Memes

It's an obvious fact that organisms do not exist in isolation.  Every individual organism, no matter how simple or complex, must navigate a world of other organisms.  Often, these interactions are antagonistic such as in predator prey dynamics.  However, individual organisms also form positive relationships with other organisms in complex webs of mutualistic benefit.  Perhaps the most startling examples of this come from mammalian studies that have shown the majority of cells contained within a mammal's body are not mammalian cells at all.  Put more plainly, most of the cells in your body aren't human!

Most of the non-human cells taking up space inside the body you think of as you are not harmful.  Indeed, most of them are likely performing useful services that help you to survive and reproduce better.  As such, their biologic interests and yours are closely aligned.  This isn't always the case, though, as anyone who has ever suffered a bacterial infection can attest.  These relationships are unpleasant precisely because the biological interests of harmful organisms and our own are at odds with one another.  Staph doesn't need to worry about your welfare in order to survive and reproduce as long as there are plenty of other bodies in close proximity that it can infect when it's done exploiting yours.  These kinds of antagonistic interactions between organisms is what differentiates parastism from mutualism.  

It is within this context that the concept of memes was born.  A provocative implication of memetics was that cultural information, when considered as consisting of replicators in their own right, might behave similarly to parasites, using hosts' resources to replicate in direct conflict with their hosts' fitness interests.  This could explain why human behavior is often so maladaptive.  It's at once a clever and compelling idea.  Unfortunately, as best I can tell it's an idea that can only be explored within the context of maladaptive behavior.  It's not at all clear to me, for instance, how you could demonstrate selection at the level of memes in cases where memes are mutualistic since selection acting at the level of the individual has equal explanatory power.

Be that as it may, even if memetics can only be explored within the context of maladaptation then it is still a useful idea worth full consideration and there are seemingly endless examples of maladaptive human behavior to explore.  One of the favorite examples that memetics proponents, particularly those that make up the New Atheist movement, like to trot out is religion.  It's no secret that Dawkins, the one who coined the term "meme," is no friend of religion and his career has taken a polemical turn against religion because he believes it to be a parasitic meme, causing people to engage in all sorts of preposterous behaviors that are against their self interest.  He's hardly alone.

There are several problems with this line of reasoning, though.  First and most obviously such arguments generally treat religion as some singular, monolithic thing.  This gives great rhetorical freedom to march out any historical instance of religion behaving badly as an example in support of the hypothesis that religion is a parasitic meme.  However, it's an approach that doesn't give much, if any, empirical traction.  It ignores the fact that different religions are VERY different and even within a particular religious taxon, such as Christianity, there is such incredible variation that different denominations are better thought of as separate species, each of which is comprised of suites of traits that can be adaptive, maladaptive or entirely neutral.  It may be that Quakers display maladaptive traits, but using the excesses of Catholicism during the Crusades as evidence of this makes absolutely no sense, yet the broad brush arguments of many of those in the New Atheist movement seem to be just that undiscriminating.

Such arguments also tend to ignore context.  Generally speaking biological traits only become maladaptive within specific contexts.  Our evolved traits that cause us to find sweet and fatty foods desirable is entirely adaptive in environments where these energy sources are relatively hard to come by.  Only in modern times when these have become available in every corner store do these traits lead to severe obesity with all its associated problems that lead to lower fitness.  Branding Islam as maladaptive because some vanishingly small number of Muslims engage in suicide bombing is a bit like branding the heart as maladaptive because it sometimes leads to cardiac arrest.

This brings us to the last point I'd like to make.  Namely, is religion really maladaptive?  By any definition, this is probably true within certain contexts.  However, is it broadly true?  The answer seems to be no.  The most comprehensive treatment of this topic is Koenig, King and Carson's Handbook of Religion and Health, now in its second edition.  It is a hefty tome of meta analyses that reviews virtually every study that has been done related to religion and health.  I couldn't begin to summarize their findings here but the relevant take home message is that more religious people, on average, live longer and have more children than less religious people.

Now, survival and reproduction are the very sina qua non of biological fitness.  If religion actually can be thought of as being composed of memes then it would seem that most of the time religious memes' interests are closely aligned with the biological interests of their hosts and, as such, cannot be thought of as parasitic at all.  Indeed, if we look at fitness through a strictly biological lens, then the fact that atheists have fewer children and live shorter lives suggests that it is atheism, not theism, that is composed of parasitic memes and needs special explanation from an evolutionary perspective.  I somehow doubt that many within the New Atheist movement would be comfortable with that conclusion, but the best empirical evidence we have seems to point in that direction.

Saturday, August 25, 2012

E.O. Wilson getting religion wrong

I just finished reading E.O. Wilson's The Social Conquest of Earth.  Written as it was for an educated yet not academically minded audience it is hardly surprising that I didn't learn much new from the book.  Nevertheless, it should serve as a handy reference for teaching in the future and I found it refreshing to see the multi-level selection approach so forcefully promoted even if, in some places, I believe Wilson overstated the case.  Unfortunately, Wilson makes a number of unwarranted and poorly informed attacks against religion.  In the future, I may take each of these in turn.  For the moment, however, I'd like to comment on one in particular since it touches on my own research.

Wilson makes a number of impassioned pleas toward the end of the book about the critical juncture the human species finds itself at.  As might be expected from a biologist, his loudest cries are for the state of the environment:

Sure one moral precept we can agree on is to stop destroying our birthplace, the only home humanity will ever have.

That's certainly a moral precept I can agree on and one that I feel rather strongly about as well.  However, Wilson goes on to say:

It will be useful in taking a second look at science and religion to understand the true nature of the search for objective truth.  Science is not just another enterprise like medicine or engineering or theology.  It is the wellspring of all the knowledge we have of the real world that can be tested and fitted into preexisting knowledge.  It is the arsenal of technologies and inferential mathematics needed to distinguish the true from the false.  It formulates the principles and formulas that tie all this knowledge together.  Science belongs to everybody.  Its constituent parts can be challenged by anybody in the world who has sufficient information to do so.  It is not just "another way of knowing" as often claimed, making it coequal with religious faith.  The conflict between scientific knowledge and the teachings of organized religions is irreconcilable.  The chasm will continue to widen and cause no end of trouble as long as religious leaders go on making unsupportable claims about supernatural causes of reality.

To put this into better perspective, Wilson just a few paragraphs earlier said:

Why, then, is it wise openly to question the myths and gods of organized religion?  Because they are stultifying and divisive.  Because each is just one version of a competing multitude of scenarios that possibly can be true.  Because they encourage ignorance, distract people from recognizing problems of the real world, and often lead them in wrong directions into disastrous actions.

So now we get to the heart of my objection.  As I read it, Wilson is essentially trying to lay the blame for environmental degradation at the feet of religion.  Moreover, he suggests that the only antidote to the destructive nature of religion's superstition is the cold rationality of the scientific enterprise.

This is particularly obnoxious to me because I have been working for the past year and a half on a project with some of Lin Ostrom's students that looks specifically at the relationship between religion and the management of natural resources.  We still have two more cases to code before we begin our analysis.  Nevertheless, it is clear from the 48 cases that we've looked at so far that religion has traditionally had extremely important roles to play in the sustainable use of resources.  For instance, religion often serves to define the physical boundaries of resources and marks those who are allowed to use them.  Religion serves monitoring functions and imposes sanctions for those who break the rules.  It also is an important source of perceived benefits that encourage users to cooperate with others.  Religion provides opportunities for leadership, repositories of local knowledge, calendars to coordinate cooperative efforts and avenues for the establishment and maintenance of social capital.  To say that religion in this context is "stultifying and divisive" is plain and simply wrong.  It is both highly innovative and creative and it leads to greater cooperation for an enterprise that is notoriously difficult.

Now, I can hear the objections already that religion is hardly necessary to provide these services.  This is a fair point.  Indeed, many groups do use secular alternatives to great effect.  Furthermore, many groups that we've studied employ a mixture of religious and secular mechanisms to govern their resources sustainably.  Nevertheless, the fact that religion is providing these vital functions should alone be enough to give us pause about actively working to undermine them.  At least it should give us pause if our primary goal is really better stewardship of the planet.  Religious means of encoding culturally important information may not be rational in the sense that Wilson and others understand that term.  They certainly weren't arrived at through a deliberate process of empirical research checked through peer review.  For that matter they often probably didn't arise as deliberate conservation efforts in the first place.  Many of them, however, have been in use for centuries and, as such, have been subjected to generations of cultural evolution which has produced finely tuned institutions, exquisitely sensitive to local environmental contexts.  Surely if biologists can't place any credence on supernatural entities and superstitious articulations of the way the world works they can at least give some respect for systems refined through natural selection!

Finally, religion is hardly unique in its ability "to distract people from recognizing problems of the real world," nor is it alone in leading "them in wrong directions into disastrous actions."  Time and again we have found cases in our work where the leading cause of the breakdown in sustainable resource management by user groups can be traced to either the privatization of the resource in question or, more often, to the usurpation of local user rights through nationalization.  In this latter case, national governments take over control of resources, eliminating any semblance of local autonomy and denying local users any collective choice rights to determine the rules they are expected to follow.  The results of this kind of policy are almost universally disastrous, leading to rapid environmental degradation.

And where did these policy notions come from?  It was decidedly not from the world's religions.  Rather, it came from western scientists and scholars whose thinking was summarized so concisely and compellingly in Hardin's Tragedy of the Commons.  This represents policy based on rational thought and enjoying strong empirical support from modeling studies and laboratory experiments.  In short, it represents exactly the sort of approach that Wilson touts as being inherently superior to the "unsupportable claims" of religious leaders.  It also happens to be completely and disastrously wrong as Elinor Ostrom's work has shown, work for which she earned a Nobel Prize.  I only hope that the damage caused by such superior, rational thinking can be repaired before it's too late for us all.

Thursday, August 23, 2012

Energy Rate Density, Fitness and Reproduction

As you (Ian and Yasha) know I have been struggling with the idea of differences between absolute and relative fitness. I just typed out something that just occurred to me. Let me know what you think. 

Not all traits/behavior may contribute to reproductive success. If we consider reproduction as a special case, then those traits become relevant that contribute to reproductive success as they can get selected and evolve. 

If reproduction does not occur in a system, then those traits will evolve (by means that do not specifically require reproduction/heredity) that contribute to...well just living and increasing/maintaining the bearers free energy rate density (Chaisson, 2011).

If the above has some meaning then bringing together the two ideas of "reproduction is a special case" and "is there a difference between absolute and relative fitness" leads you to this conclusion, traits that contribute to increasing free energy rate density can be broken down into two types those that rely on reproduction and thus contribute to increasing reproductive fitness and those that do not contribute to in any conceivable way to increasing reproductive fitness. 

In the second scenario those traits that rely on reproduction and contribute to a increase in reproductive fitness are traits that increase relative fitness of an organism in a population over time. 

The first scenario describes contribution of a trait to absolute fitness, where a trait might not have anything to do with reproduction or reproductive success. It just contributes to maximizing free energy rate density..just living. 
        Chaisson, E. J. (2011). Energy rate density as a complexity metric and evolutionary driver. Complexity, 16(3), 27–40. doi:10.1002/cplx.20323

Wednesday, August 22, 2012

The meaning of the adaptation to tolerate lactose.

The question that is most often asked about lactose tolerance is that if drinking milk is an evolutionary adaptation shouldn't we continue to reap its fitness benefits? Although this question may be frowned upon by individuals who study evolutionary biology it is an important question to answer as it addresses the issues that  are important to understanding of evolution; adaptation and natural selection. 

I will explore this question in two parts first I will explain the adaptation of lactose tolerance and then I will explore how natural selection effects life history evolution. 

Is Lactose tolerance an adaptation? 

Lactose tolerance occurs due to a genetic mutation(s) that confers an ability to digest lactose from milk. Lactose tolerance appeared as a fortuitous mutation, yet it got selected as a result of the fitness benefits it conferred; it had beneficial effects on the adaptedness (absolute fitness) of individual humans within an environmental context. Natural selection then occurred as a result of differences in adaptedness of individuals within a specific population; i.e. some individuals could drink milk into adulthood whereas others couldn’t. Over time, those individuals that could drink milk into adulthood survived and reproduced at relatively higher rate than those who could not. Over many generations, through the process of adaptation the trait for digesting lactose became adaptive within a spatio-temporal context.

Even though the trait arose as a fortuitous mutation it became adaptive as it created differences in absolute fitness and set stage for natural selection to occur. Lactose tolerance gene was definitely an adaptation to milk drinking in the spatio-temporal context it evolved in; must this mean that this trait is as adaptive today as it was in our past? Does a trait’s noble legacy justify its credentials in the present? This may not always be true and the answer depends on the differences between past and present and the nature of life history evolution.

It is important at this point to understand that all adaptations have three aspects.

a) Historical; an adaptive trait is present today in an organism because it provided fitness benefits to its bearers and there was a selection for the adaptive trait.

b) Spatial: An adaptive trait is a specific solution to a problem posed by a feature of a given environment.

c) Eventual: Adaptive traits have the ability to confer (present and future) fitness benefits to its bearers.

Whether or not an adaptive trait persists through time depends on a number of factors; the environment being the most critical of them. If there are minimal changes in the environment (over evolutionary time) such that the plasticity allows the trait to persist, then the trait remains a legible solution to the problems posed by the environment. On the contrary, if the environment has changed substantially enough so that the plasticity of the trait does not buffer the changes, then the trait finds itself in uncharted waters. Sober pointed out in “The Nature of Selection” that “the benefits that account for a traits fixation need not persist into the present. “The benefits that account for a traits fixation” are governed by the environment (Sober, 1993).

If one considers just the historical aspect of an adaptive trait then “a trait can be an adaptation for performing some task, even though performing that task in the present environment confers no benefit” (Sober, 1993).
This statement can be misunderstood as the reader might comprehend that a traits noble legacy justifies it present credentials. An adaptive trait remains an adaptation no matter what happens. I would like to clarify what I think Sober meant for the reader to read between the lines; an adaptive trait remains an adaptive trait, retrospectively. A trait is an adaptation just because it was an adaptation in the spatial context it evolved. The trait conferred fitness benefits to its eventual bearers. The trait will still be called adaptive; the process which shaped the trait will still be called adaptation, but retrospectively. Whether an adaptive trait is adaptive today depends on the environmental context of the trait. If the environment is substantially different from the environment in which the trait evolved and became adaptive then the trait may not confer any fitness benefits (Remember that the trait is still adaptive but…you guessed it…retrospectively). If the environment changes, the trait remains adaptive looking at the past; whether the trait still persists as an adaptation in the future is another issue altogether.

There are three scenarios a trait may experience if the environment changes; a) the trait may not confer any fitness benefits, i.e. remain neutral and adaptive retrospectively; b) the trait may happen to confer fitness benefits, persist being adaptive; and c) the trait confers negative fitness benefits and become maladaptive.
Going back to the adaptive trait of Lactose tolerance, we can either say that Lactose tolerance was an adaptation in the spatio-temporal context that favored its prevalence or lactose tolerance is an adaptation retrospectively. Both statements are correct as long as you understand the definition of an adaptation. The question therefore is not whether lactose tolerance is an adaptation. It most definitely is! The question is whether lactose tolerance is an adaptation in today’s environmental context? 

In the arid climates of Middle and Near east dairy has been suggested to be the major source of clean uncontaminated water (Cook & Al-Torki, 1975). The individuals that could drink milk into adulthood happened to have higher relative fitness than those who could not. In northern Europe dairy was the source of calcium, this must have been crucial in place where there is very little sunlight (Flatz & Rotthauwe, 1973).
Thus the trait was selected and as the populations of individuals travelled across the world the trait travelled with them. In certain places the trait might have been still adaptive; yet, in other places the adaptive trait might have lost its relevant environmental context. Rehydration through consumption of dairy is not a necessity when you live next to a river, for example.

Thus we can say that in certain populations in the past (and today) the adaptive trait of lactose tolerance lost its relevance, as it could not confer fitness benefits. It is lingering in our gene pool as a consequence of fitness benefits it conferred to its bearers in their environmental context. Those fitness benefits are not relevant in those populations whose environmental context has changed. Thus lactose tolerance does not remain an adaptation in those populations; however, that does not take away the adaptive legacy of the trait. The trait has become a not-so-benign ghost of Christmas past.

Lactose Tolerance is a mal-adaptation

Now that I have established that a trait can lose its adaptive significance in a changed environmental context I will try to make the case that this trait is not just a neutral adaptation but has the potential to be transformed into a mal-adaptation in todays environmental context. Lactose tolerance and the resultant consumption of milk have been linked to many chronic diseases of the western civilization. Chronic consumption of milk has been associated primarily with auto-immune diseases (Type 1 Diabetes, Rheumatoid Arthritis, and Multiple Sclerosis) (Elliott, Harris, Hill, Bibby, & Wasmuth, 1999; Malosse, Perron, Sasco, & Seigneurin, 1992), consumption of dairy has also been correlated to prostate cancer and insulin resistance (Pereira et al., 2002; Qin et al., 2004). The ghost-adaptation of lactose tolerance is making us realize the necessity of changing our ways (I couldn’t help myself there ). Lactose tolerance today is a mal-adaptation as the trait was previously selected for by natural selection, lost its relevance, and now is becoming a crucial factor in the development of chronic diseases.

Natural Selection and Life History Evolution

There is another important aspect to the “adaptation” of consuming dairy into adulthood. It is centered on the workings of natural selection.

Natural selection operates most quickly on traits and behaviors that are expressed during the reproductive years of the life cycle. A trait that hampers reproductive ability in the young will be quickly eliminated from the population. A trait that is expressed in the in the older individuals will be removed much more slowly. As lactose tolerance was beneficial for individuals within a certain environmental context it got selected irrespective of the long-term effect it caused.

The following table may help to explain which traits get naturally selected. Traits and adaptations may have in all four aspects: a) short term benefit, b) short term cost, c) long term benefit, and d) long term cost

Traits that have short (during reproductive years) and long term benefits (longevity) will get naturally selected so will traits that have short term benefit and a long term cost. Traits with short term cost will get weeded out if they negatively affect an organisms’ fit with the environment. Lactose tolerance, in todays changed environmental contexts falls into the category of traits that have short term benefit and long term cost.


Thus, the question, “if lactose tolerance is an adaptation shouldn’t we continue to drink milk?” has two sub-questions. First, is lactose tolerance an adaptation in todays environmental context? And second aspect deals with nature of life history evolution and natural selection. The answer to the first question tell us that lactose tolerance is does not remain an adaptation in a changed environmental context, moreover it has become a mal-adaptation due to enabling of chronic consumption of milk. Dairy consumption has been correlated locally as well as globally with many diseases of civilization. The answer to the second question addresses the issue that a trait that confers fitness benefits in reproductive life will tend to get selected even though it has long term costs.

Summary Statement: Lactose tolerance is a retrospective adaptation that has the potential to become mal-adaptive in a changed environmental context. 


Cook, G. C., & Al-Torki, M. T. (1975). High intestinal lactase concentrations in adult Arbs in Saudi Arabia. British Medical Journal, 3(5976), 135–136.

Elliott, R. B., Harris, D. P., Hill, J. P., Bibby, N. J., & Wasmuth, H. E. (1999). Type I (insulin-dependent) diabetes mellitus and cow milk: casein variant consumption. Diabetologia, 42(3), 292–296.

Flatz, G., & Rotthauwe, H. W. (1973). Lactose nutrition and natural selection. The Lancet, 302(7820), 76–77.

Malosse, D., Perron, H., Sasco, A., & Seigneurin, J. M. (1992). Correlation between milk and dairy product consumption and multiple sclerosis prevalence: a worldwide study. Neuroepidemiology, 11(4-6), 304–312.

Pereira, M. A., Jacobs Jr, D. R., Van Horn, L., Slattery, M. L., Kartashov, A. I., & Ludwig, D. S. (2002). 

Dairy consumption, obesity, and the insulin resistance syndrome in young adults. JAMA: the journal of the American Medical Association, 287(16), 2081–2089.

Qin, L.-Q., Xu, J.-Y., Wang, P.-Y., Kaneko, T., Hoshi, K., & Sato, A. (2004). Milk Consumption Is a Risk Factor for Prostate Cancer: Meta-Analysis of Case-Control Studies. Nutrition and Cancer, 48(1), 22–27. doi:10.1207/s15327914nc4801_4

Sober, E. (1993). The nature of selection: evolutionary theory in philosophical focus. University of Chicago Press. Retrieved from

Saturday, July 14, 2012

Why we still wear pants

Peter Turchin recently published a series of blogs (part 1 and part 2) addressing the question of why westerners wear pants.  It's a story I'd heard before years ago in a comparative Indo-European studies course, but not from an expressly evolutionary perspective and not with Peter's flare.  It's a good story, particularly for introducing cultural evolution, and I don't want to spoil it for those who haven't heard it before.  Nevertheless, not much about this post will make sense if I don't at least mention that wearing pants came about whenever riding horses became an important part of warfare.

As much as I like the story, I made what I thought was a somewhat innocuous comment saying that I would like to see a follow up series of blogs that explored why we still wear pants.  After all, very few people ride horses and, aside from some special exceptions, horse cavalry became obsolete in World War 1.  However, not only has the wearing of pants continued, it has spread, both to societies we've come into contact with and to women within our own society.  This spread has happened without any obvious adaptive advantage.  Moreover, this persistence and spread has occurred despite available alternatives and social movements, such as the androgynous movement of the 1980s, that attempted, and failed, to change these established practices.

Peter's response to this question, while not exactly surprising, was surprisingly dismissive.  His position is that there is no need to explain when cultural traits fail to change.  For him, the lack of change is the null hypothesis.  In his own words:

The null model is dp/dt = 0, where p is the frequency of the trait, and dp/dt it’s (sic) rate of change. If there is change, then dp/dt = c, or dp/dt = cp, depending on the details of how the trait changes. In any case, the greater the rate parameter, c, the faster the trait will change. So if c is high enough you will have yearly changes of fashion, if c is small enough, then it will take decades or even centuries.

The failure of something to change, in Peter's view as I understand it, can simply be dismissed as normal inheritance.  In the absence of variation and/or in the absence of selection pressure to change, we simply go on as we've always done.

I object to this position on a number of fronts.  To begin, it appears to be an assumption, not an empirically established fact.  Moreover, all these equations really establish is that some traits change faster than others, hardly a startling revelation.  What they fail utterly to do is account for why some traits change faster than others.  The salient question, for me, is why dp/dt should ever be zero, or even near zero. 

It is, of course, entirely plausible that Peter is right, that the failure of this particular trait to change might be due to simple inertial processes.  However, this is far from the only possibility.  We need only look to biological systems to see why this is so.  Robustness, the propensity of a system to continue functioning in the face of perturbation, is a general property of complex, evolved systems.  The structure of DNA and the genetic code are robust to mutations.  Proteins similarly tend to perform their functions even with amino acid substitutions.  This robustness is evident all the way up the hierarchy of biological complexity.  Even developmental systems are robust to changes in metabolic pathways. 

I see no logical reason to assume this general property of biological systems, a property that is an adaptation in its own right, should somehow no longer hold true once the level of complexity moves outside the skin of the individual organism.  Moreover, if evolutionary approaches to understanding human culture are to meet their full potential, they must grapple with practical problems in the current world, many of which represent historical patterns from which groups seem almost incapable of escaping.  For instance, Nisbett andCohen have traced modern rates of male violence in the southern United States to Celtic herding cultures, an ancestral pattern that has persisted long after herding faded out as a way of life.  Similarly, Robert Putnam has traced failures of democratic institutions in southern Italy to patterns of social capital building that go back 500 years.

Treating the persistence of these problems as nothing more than null hypotheses drastically reduces the chances of finding real solutions.  Aside from blinding ourselves to the root causes of recalcitrance, robustness paradoxically makes evolvability possible.  A handful of textbook examples notwithstanding, it is rare for a single mutation in biological systems to be adaptive.  Most often, adaptations arise from a series of mutations.  Fragile systems, however, are relatively incapable of building pools of useful variation since any slight change is likely to lead to suboptimal performance.  Robust systems, by contrast, tend to build up pools of variation, some combination of which may prove adaptive when new niches present themselves or existing environmental conditions change.

As for the question that ultimately motivated this post, I have no idea why we are still wearing pants.  If I were to hazard a guess, I would say that once pants became associated with warrior castes they acquired protection by virtue of prestige bias.  This in itself, though, might not have been enough to ensure the practice persisted.  More likely, the wearing of pants started to get tied to concepts in addition to warrior attire.  For instance, pants became associated with markers of gender identity, group heritage, etc.  In other words, it became connected to many other cultural constructs in intricate webs not unlike the way genes often have pleiotropic effects in gene networks.  If so, then wearing pants could become difficult to change even if there were compelling reasons to do so.

Sure, this is all purely conjecture at this point.  However, it hopefully goes some ways toward demonstrating that lack of change is a worthy subject for evolutionary study.