Friday, September 28, 2007

Week 7: Cultural, linguistic, genetic diversity patterns II

For this week, please read the following, ideally in the order listed:

[suggested] Reread Pagel & Mace, 2004, starting at “Cultures and gene flow,” p. 276

Cavalli-Sforza et al., 1988. Reconstruction of human evolution: Bringing together genetic, archaeological, and linguistic data.

Sherman & Billing. 1999. Darwinian gastronomy: Why we use spices.

McDade et al., 2007. Ethnobotanical knowledge and child health in Bolivia.

[Optional] Ackland et al. 2007. Cultural hitchhiking on the wave of advance of beneficial technologies.


This week we will a) look explicitly at the relationships between genetic diversity and linguistic diversity and their relation to human evolution, b) continue exploring cultural diversity gradients, focusing on a gradient in the use of spices, derived from plants, and c) explore how maternal knowledge about plants effects child health. I think these connections are pretty amazing, and I hope you enjoy the papers. This last article, in a sense, brings us full circle back to some basic life-history considerations.

Keith Hunley, an assistant prof of Anthropology at UNM, will lecture on Tuesday and asked that we read Cavalli-Sforza as background for his talk. Cavalli-Sforza pioneered the use of gene frequency data and allied methods to study the movements and evolution of people and their biological and linguistic traits. This paper has some jargon and a genetics and evolution bent, but focus on the overall findings and implications. The last portion explicitly relates the overall findings to human ecology. Think about the forces that selected for general language ability and, at the same time, the partitioning of this human universal into about 6900 varieties.

There’s debate about the correspondence between patterns of linguistic and human genetic diversity patterns. Some authors have reached different conclusions from Cavalli-Sforza. Think about likely mechanisms underlying linguistic & genetic evolution. Why would or wouldn’t you expect agreement between them? What ecological factors likely affect them? And how might you test for relationships?

Sherman & Billing take a macroecological approach to analyzing patterns in spice use across the globe. It’s an innovative look at cultural diversity gradients and at a hypothesis for an underlying mechanism. What other mechanisms could underlie this pattern? Paul Sherman wrote a well-cited paper called “The Levels of Analysis,” which the authors cite in the article we read and which argues that researchers should consider both the “proximate” and “ultimate” explanations for traits. A proximate explanation focuses on physiological and genetic mechanisms, while an ultimate explanation focuses on underlying evolutionary reasons. For example, a proximate explanation for the spiciness of chiles is the concentration of the tongue-searing biochemical capsaicum and the prescence of genes coding for it. An ultimate explanation is the adaptive benefit to chiles of deterring mammals from eating their fruits, because mammals are more likely to chew the seeds and drop them too close to the parent plant or deep underground. Birds are much better dispersers of chile seeds and, not surprisingly, don’t taste capsaicum. What are possible proximate reasons people in warm climates use more spices, and are they compatible with the authors’ hypothesis for ultimate reasons?

“… the intergenerational transmission of knowledge regarding the use of available plant resources has historically been an essential function of culture.” McDade et al., 2007

McDade et al., 2007, looks at the relationship between parent’s ethnobotanical knowledge, or knowledge of local plant resources, and the health of their children among the Tsimane, a foraging society in Bolivia. It links together several themes we’ve discussed, including diversity gradients, health and local ecology, height differences, human learning period, intergenerational knowledge transfer, and longevity. Try drawing a diagram linking these ideas. How would you expect spices with anti-inflammatory properties, such as turmeric, to affect longevity, and why? How might gradients in plant and spice diversity affect linguistic patterns? How could you test for such relationships?

Lastly, I want to encourage the quieter voices in the class to let us hear your thoughts and insights a bit more. Likewise, I want to encourage bolder students to leave a bit more “air time” for others to enter the discussion, even if that means the occasionally silence. One of the strengths of a diverse class is the potential for a diversity of perspectives. And just as species diversity includes both “richness” and “evenness,” I want to maximize the diversity of our discussions, with all participating in a significant way. Thanks for your consideration and effort on these points.

See you Tuesday.



admixture – mixture of two or more genotypes; mixing of genetically different groups

allele – version of a (polymorphic) gene. For example, a population of wild rose that has both red and white flowers has different alleles for flower color.

bootstrap – (also called bootstrapping) a statistical technique for making educated guesses about a population by randomly sampling with replacement from the sample you have, creating distributions of those samples, and assuming the distribution of those samples mirrors the “sampling distribution” of your original population. So if you just have one sample from a population and you don’t think the pop has a normal distribution, you use the distribution of samples of your real sample to infer what the distribution of actual samples from the true population what look like. Regardless of the specifics, it’s a powerful method for inferring characteristics of a population based on a single, usually large sample. Cavalli-Sforza used bootstrapping to test hypothetical human evolutionary “trees” using a large sample of genetic distances for genes shared by human populations. If you want to know more, read “The Bootstrap Conjecture” in

demographic bottleneck – a sharp reduction in population size, which tends to reduce genetic diversity the same way taking a small handful of M&Ms from a giant bowl is unlikely to capture the variety of colors in the original “population”

electrophoretic – involving electrophoresis, which is the identification of organic compounds via the distance they move through a gel when under an electric charge; small compounds move faster and so further in a given time

gene frequency – relative frequency of a given gene in a population

genetic distance – relative genetic dissimilarity between individuals, populations, or species. A common null hypothesis is that the genetic distance between two samples, such as between two populations of people, indicates the amount of time they’ve been separated. The underlying reason for this null hypothesis is that much of our DNA, including the “genetic marker” portions used for many studies, has no real effect on our genetic fitness or adaptedness yet still accumulates “adaptively neutral” mutations at a low, stable, background rate that can be used as a “molecular clock.” The number of unshared mutations between populations on such a genetic marker represents the “ticks” of this clock: the time the two groups have lived apart, not interbred, and undergone separate evolution. What’s an alternative hypothesis for the genetic distance between two populations?

genetic drift – change in the frequency of one or more genes in a population due to chance, as because some members happen to have more offspring for reasons unrelated to adaptatedness; along with natural selection, genetic drift is one mechanism behind evolution; the frequency of a given gene is more likely to “drift” one way or another in a small population, just as a small number of coin tosses is more likely to give a non-50/50 ratio of heads/tails than a large
number of coin tosses

linkage analysis – an analysis of the amount of linkage between genes. Linkage is the tendency for genes located near each other on a chromosome to be inherited together.

maximum likelihood – statistical method for evaluating phylogenetic trees that favors the “tree” with the highest probability of being correct given your constraints

maximum parsimony – statistical method for evaluating phylogenetic trees that literally favors the “tree” that requires the fewest evolutionary changes to explain the variation in a group of related organisms

phylogenetic tree – evolutionary family tree, as of genes or of languages.

polymorphism – alternate version of a trait or gene

population – the individuals of a species living in the same area at the same time and so having a good chance of interbreeding; Note that biological evolution occurs within populations as the frequency of genes changes among its members.


Wenyun said...

For meat-based dishes, as my experience, most of them are cooked. Heat may be the most important fighter in the battle of bacteria. However, when we cook salad which most of them eaten rawly, we need spice to kill bacteria. So why do not consider vergitable-based dishes? And for keeping meat longer, we generally use salt. I wander why we need mixture lots of different spices to keep meat suvival instead of one simple thing, salt.

Wenyun said...

I think high spice diversity may be more related to high plant species diversity. People live in those place have more resouce and more choice.

Steven M. said...

I think the data in the Cavalli-Sforza provides good support for using languages as a surrogate for distinct "culture groups" that probably have a shared ancestry. This was done in the papers we read last week, and I believe that this paper supports that assumption.

Justin Smith said...

Following Wenyun's first question about Sherman and Billing's exclusion of vegetarian dishes: if vegetable-based meals show the same patterns of spice-use as meat-based recipes, would parsimony favor the null hypothesis that spices aren't used to fight meat-borne bacteria? It seems like an important control group has been neglected.

Dan said...

How accurate is using temperature as a proxy for prevalence of diseases? Obviously there are more diseases at the equater than at the poles. But aren't there fewer diseases in say an aird environment high temperature than a tropical regions of the same temperature. It seems that there may be several confounding variables which where overlooked.

tlvandeest said...

In the Sherman and Billing article, they mention that animals are not using spices to combat the bacteria in their diet but are eating vegetation. Could the animals be using other plants to deal with the same problem? And if the use of plants to deal with microbes is evolutionary then wouldn't you expect similar uses in animals? If spices and cooking both kill bacteria and microbes, as Wenyun was saying, then wouldn't you expect less use of spices in modern humans due to cooking than in say other primates and animals where this option does not exist?

Deepta said...

Not sure if this is the same question as above, but the Sherman and Billings article mentions that there is not much evidence for animals consuming spices. Is this actually the case, or is there a possibility animals are consuming the plants that provide the spices? Also, what guarantee do we have that animals need the immunity provided by these spices, they may not be susceptible to the same illnesses.

Justin Smith said...

Cavalii-Sforza et al. postulate that language replacement without full genetic replacement is a recent phenomenon, confined to the past 5000 years due to "elite dominance." Before 5kya, they assume complete genetic replacement of expanding populations over preexisting populations, such that linguistic phyla and genetic clusters moved together completely. What is elite dominance and how do we know that elites have developed only recently (p. 6005)? How can this claim apply to both the Eastern and Western hemispheres where human populations were separated before this 5kya transition point?

dtinucci said...

Looking at the Cavalli-Sforza article, I am unclear on whether African DNA is reputedly oldest, or if these researchers arbitrarily began from this point?

As a comment applicable to New Mexico culture I submit this info on Sage. Although sage typically is identified with our southwest desert biome, the bushy plant originates from the Mediterranean region. It is reputed to be historically one of the most used herbs. In fact, its scientific name. Salva officinalis, descends from the latin word salvere - to save. Sage's medicinal properties extend to its leaves, flowers and stem, and was generally applied to the respiratory tract were it is effective in suppressing various infections. As a culinary ingrediant, it remains popular with pork or chicken - which may give us a clue in relation to our spice article, as pork is famous for its toxicity.

dodegard said...

From the Cavalli-Sforza article, children whose mothers do not frequently go to the major city have less CRP in their blood. Why does isolation from cities increase the health of foraging group's children? Is it because of an increase in exposure (by proxy of the mother) to pathogens or some other cultural explanation?

Fred Whiteman said...

In regards to the Sherman and Billing article, what implications do these findings have for humans not from hot climates who enjoy spicy food? Have we acquired a taste for it, or, like our equatorial relatives, are we predisposed to favor spicy food after childhood? I personally come from long lines of northwestern Europeans and Ashkenazi Jews who love their spicy food. If we are predisposed to favor spice, would that indicate that it is availability of spice that governs the distribution of its use?

Michael said...

The process in which LEK was measured in McDade et al. seems a bit shaky. What would classify as “other” on the multiple choice questionnaire? And how would “other” be scored in relation to the defined choices? Also, as the elders were used as repositories of local ecological knowledge, how much of the local ecology has changed in the last 50 years given their slash-and-burn agricultural practice?

Michael said...

Regarding my previous posting, Reyes-Garcia et al. (2007), in examing the Tsimane , showed that when the ethnobotanical skill of the male household leader is doubled, the amount of forest leveled through slash-and-burn agriculture is reduced by 25%, showing that those individuals with a greater knowledge base of the utility of the forest (and perhaps also a greater reliance), are more reluctant they are to chop it down.

Wenyun said...

In Sherman and Billing's paper (1999), figure 3 shows how popular those spices are. I wonder whether it is related to the age of the spice. If it appealed or is discovered early, it may be more popular. Of course, it should also related to its habitat, whether the habitat is narrow or wouldspread.

helen elizabeth said...

McDade et al suggest they have controlled for most confounders in this paper, but did they consider other realms of information (IQ, social, political)? If they really want to isolate the effect of ethnobotanical knowledge on health and fitness of children it would seem that they would have to control for both the general or fluid intelligence of the parents-- assuming there really is a correlation between the two.

They mention in the discussion that parents could also be better foragers and hunters. However, this furthers the idea that it may not just be local ethnobotanical knowledge (LEK) that’s contributing to healthier children. Those with more LEK are more likely to more skilled in a number of areas that contribute to healthier children.

helen elizabeth said...

In response to Wenyun and Justin. Sherman and Billing have a more recent paper "Why Vegetable Recipes Are Not Very Spicy," in the June 2001 issue of Evolution and Human Behavior (Vol. 72, pp. 147-163).

They analysized 2,129 vegetable recipes from 107 traditional cookbooks of 36 countries and found that meat dishes always used more spices than vegetable dishes.

Wouldn't the dead plant cells continue to be better protected against bacteria that the cells of dead animals-- who no longer have a functioning immune system?

Justin Smith said...

Thanks, Helen.

dodegard said...

What other uses would plant knowledge have for foraging groups other than medicinal reasons?

tlvandeest said...

The McDade et al article states that frequwent travel by the mother to San Borja increases a child's level of CRP. But what about the amount of contact between the Tsimane and others living in the rural areas with them? Is it only due to travel into the dirtier city or would the same patterns appear in contact with other groups? Also did the researchers measure their own presence and its possible influence on the CRP levels of the children in any way, in terms of a higher pathogen load as David suggested?

paul said...

If you eat seviche in Peru, they 'cook' the raw fish with lime juice. What's goin on there?

paul said...

In Sherman & Billing's ‘costs of spices’ section, they don’t bring up again the fact that plants are often manufacturing these secondary products to make themselves less appealing to herbivores (not just bacteria). So they’re designed to be hard to unpleasant, noxious, poisonous, etc. And kids and folks that aren’t accustomed have a really hard eating spicy food. So we’re drawn to spices for their benefits, but still have a system that (sometimes) tells us not to eat the stuff.

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