Mashco-Piro Video on BBC

The BBC has a video up on their website of footage capturing a remote forager population in Peru. The video isn't very clear but its worth checking out and they do a good synopsis.
See it here.

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.

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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.

Bill

Glossary:

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 http://www.uvm.edu/~dhowell/StatPages/Resampling/Bootstrapping.html.

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.

Week 6: Cultural, linguistic, & genetic diversity patterns 1

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

1. Moore et al. 2002. The distribution of biological & cultural diversity in Africa

2. Collard & Foley. 2002. Latitudinal patterns & environmental determinants of recent human cultural diversity

3. Pagel & Mace. 2004. The cultural wealth of nations.

4. (Optional) Nettle. 1998. Explaining global patterns of language diversity. [Nettle

5. (Optional) Cashdan. 2001. Ethnic diversity and its environmental determinants.

6. (Very Optional) Serre & Paabo. 2004. Evidence for gradients of human genetic diversity

Maps: (top) topography; (2nd) annual precipitation; (3rd) vascular plant species diversity, (bottom) world language diversity

Click on these maps to see them in greater detail.

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Humans are part of ecological systems and have various ecological relationships and associated life history patterns. Then again, unlike other large mammals, humans have permanent settlements on every continent and in almost every known terrestrial environment. Humans are relatively genetically homogenous, yet we display astonishing cultural and linguistic variability that follows clear geographic patterns. Is that variability a function of environmental variables, like climate or ecosystem type? Where human cultural patterns mirror biogeographic patterns of other species, are humans responding to the same forces? In the same ways? Why or why not, and how do you test such questions anyway? To start with, how do you fruitfully think about variation in cultural and social patterns—as discrete entities, as clines, or otherwise? Are these differences comparable to other biogeographic differences, and why? More broadly, what is the relationship between culture, language, and environment? Finally, how does human life history, such as lifespan and learning period, factor into such patterns and relationships?

These are some of the questions we’ll ponder and discuss over the coming two weeks. You will struggle with these ideas, occasionally you will triumph, you will laugh, you will cry. I’ll provide Kleenex.

On a more serious note, carefully read the required articles and, if time, the abstracts and figures in the optional articles. Moore et al., 2002, focuses on the relationship between language “richness” (see Glossary below) and species richness in Africa. Collard & Foley, 2002, takes a macroecological look at latitudinal patterns of cultural diversity and possible environmental determinants. Pagel & Mace, 2004, is a good, readily digestible review of current hypotheses on the relationship between culturo-linguistic diversity and environmental variation.

The optional articles provide good reference for the required ones and offer additional hypotheses. Nettle is very active in debates about linguistic diversity, and this paper gives his most widely-known view, which Pagel & Mace summarize and reference. Cashdan has done lots of work with hunter-gatherers and looks carefully at several ecological variables. If you are interested in reading more or following this topic for your project, Nettle and Cashdan are great starting points. Serre & Paabo provides some good recent context on the relationship between human genetic & linguistic patterns, but it’s useful here just for context on how human mating and migration patterns relate to linguistic patterns; we’ll focus explicitly on this topic next week.

If you come across terms in the papers you don't know, consult the Glossary below for reference and understanding. You don't need to memorize these terms, but understanding these concepts will help with the papers.

Ciao,

Bill

p.s. Also consider that languages and cultures, like species, are disappearing at a clip. A recent NYT article (http://www.nytimes.com/2007/09/19/science/19language.html?em&ex=1190433600&en=7e3479621ae1b054&ei=5087%0A)

estimated that one of humanity’s approximately 6900 languages is “lost” every two weeks. Indeed, language and cultural documentation and preservation is an active field, and a major thrust is the tight link between biological and culture-linguistic diversity.

Glossary:

allopatry – separation of a population into two or more groups via a physical barrier, such as a mountain chain or a river; allopatric speciation is the formation of two or more species as such physically divided populations genetically and behaviorally diverge

biome – one of the Earth’s main, usually terrestrial, ecosystem types, such as desert, tropical rain forest, and tall-grass prairie

carrying capacity – the maximum population size of a given species that a given environment can support relatively stably over time

correlation – in statistics, the strength and direction of the linear relationship between two variables

diversity, species—in ecology, a measure of the diversity of species in a given area that considers both “richness,” or number of species, and “evenness,” or evenness of the population sizes of those species

endemic—native and often unique to a given area

evapotranspiration—the transfer of water vapor from Earth's surface to the air from evaporation and transpiration (transpiration is the release of water vapor from plant leaves & stems as a byproduct of photosynthesis) ; potential evapotranspiration is the maximum water vapor an ecosystem could release if it got enough rain.; actual evapotranspiration is the amount of water vapor an ecosystem does release given the average precipitation it usually gets.

genetic marker— a known DNA sequence whose presence and variation can be used to infer the degree of relatedness among groups of organisms

horizontal transmission— transmission, as of a word’s meaning or a custom, within a society other than between parent and child (i.e. other than “down the generations”)

PCA (principal components analysis)— a statistical technique for reducing the number of dimensions of interest among a group of variables; generally, it helps you see which attributes of a dataset contribute most to the patterns of interest; it’s a complex idea that you don’t really need to know…I’m just defining it generally because a paper refers to it

phylogenetic tree—a tree-like diagram showing the evolutionary relationships among species or other entities sharing a common ancestor

population —in ecology, the individuals of a given species living together and interbreeding in a given area

productivity—in ecology, the amount of new living (plant) tissue produced, usually over a year’s time[so warm areas with high precipitation produce lots of new plant material per unit time and so have high productivity]; Gross primary productivity is the total CO2 transformed into living tissue, while net primary productivity is this "gross" amount minus the amount used for the plant's metabolism

reproductive isolation—the separation of two or more groups from possible interbreeding; over time, reproductive isolation often promotes the formation of distinct species, or speciation

richness – number or variety, as of species, languages, or cultures. (e.g. The endemic plant species richness of New Mexico is simply the number of plant species native to the state.)

Rapoport’s rule – the tendency for species range size to increase with increasing latitude (i.e. species at high latitudes tend to occupy large ranges and vice versa)

spatial autocorrelation— the degree of spatial, usually geographic, clustering among features of interest; for example, closely related species tend to have ranges that are spatially autocorrelated simply because they descend from a parent species that presumably lived in the general area (i.e. their ranges aren’t clustered simply because the species have similar niches); very generally, it says two points close together are more likely to be similar than two points further apart

species-area relationship – the positive relationship between the size of a habitat and the number of species it can support and that you'll find there [how might this logic be extended to human ecology?]

sympatry – (literally, “same father”) deriving from a single parent species and living in the same area; so sympatric speciation is the formation of two or more species from the same “parent species” without the help of some obvious barrier to interbreeding

vertical transmission—transmission, as of a word’s meaning or a custom, between parent and child (i.e. “down the generations”)

Contributed blog: density dependence and human body size

Greetings human macroecologists,

I asked Rob Walker, the lead author on one of our papers for next week ("Growth rates and life histories in 22 small-scale societies"), to blog about some of his research and his thoughts on what determines adult body size in humans. Some of the exciting and relevant features of Rob’s research include his argument that there are two pathways to small body size. One driven by resource limitation that causes smaller growth, and the other by high mortality. I am biased to favor this view because Rob is an old friend and collaborator and more importantly, his view agrees with the Charnovian perspective we covered in class (remember the equation with growth over mortality? – Rob’s model shows the same predictions as that model we went over). Think about how these processes of body size change might relate to the patterns demonstrated in Ruff and the potential implications for H. floresienses (to the degree that insular dwarfism may be a possible explanation for this dwarfed hominid).

Rob has written a slew of papers on human life history and behavioral ecology. To check out his other papers go to his homepage.

Here’s Rob’s blog:

I have some general interests in the evolution of the human life course and especially factors that influence patterns of growth and development. To prepare the paper on ’22 small-scale societies’ that you are reading, I started putting together data from as many societies as I could that had life-history information (e.g., growth rates, age at menarche, first reproduction, and age-specific mortality). I wanted to get a better feel for the overall variation in these traits across human populations. We were able to show that in general larger, better-nourished societies have faster/earlier growth and development (we call this the conventional model). However, while the sample is rather small, there is also some indication that societies that suffer from high mortality also grow relatively fast (relatively given their adult body size, a proxy for energetic intake). This may support the general life-history model where higher mortality prompts faster growth and development in order to get past the high mortality juvenile stage (or high mortality at small body size).

The results from this paper led to some more thinking about how mortality, resource limitation, and growth related to patterns in size and density dependence seen among contemporary hunter gatherer populations. This led to the development of a life history model for human body sizes – a manuscript presenting the model can be found here.

Here's a non-technical summary of that paper:

Average body size ranges immensely across human populations. Many of the world’s smallest populations, like the Agta hunter-gatherers in the Philippines, live on islands at relatively high population densities. We show that population density has a negative effect on adult body mass across hunter-gatherers. Humans slow down growth and development and demonstrate smaller adult body sizes in high population density contexts presumably because of less food and more disease. In addition, there is evidence of selection for relatively faster/earlier development in societies that suffer from high mortality. We interpret this finding as natural selection for earlier reproductive maturity (menarche and first birth), and consequent smaller adult body size, in high mortality regimes in order to more quickly pass into the safer adult stage. In sum, comparative results support density-dependent effects on body size that act through two pathways (energetic constraints and juvenile mortality) at varying intensities in different societies contributing to a nearly two-fold range in body size across human populations.

These ‘two pathways’ to smaller adult size are summarized in the following figure:

Cheers,

RW

Readings for week 5: variation in human body form part 2, the role of density dependence

This week we are reading a few papers that establish links between life history theory and body size evolution in general and also serve to better acquaint us with the empirical patterns of body size and growth in living humans. (note: these papers are slightly different from what's on the syllabus! We substituted Crimmins and Finch with Palkovacs)

The assigned papers are as follows:

Walker, R., M. Gurven, K. Hill, A. Migliano, N. Chagnon, R. D. Souza, G. Djurovic, R. Hames, A. M. Hurtado, H. Kaplan, K. Kramer, W. J. Oliver, C. Valeggia and T. Yamauchi
2006 Growth rates and life histories in twenty-two small-scale societies. American Journal of Human Biology 18(3):295-311.

Palkovacs, E. P.
2003 Explaining adaptive shifts in body size on islands: a life history approach. Oikos 103:37 - 44.

Stiner, M. C., N. D. Munro, T. A. Surovell and E. Tchernov, Bar-Yosef, Ofer
1999 Paleolithic Population Growth Pulses Evidenced by Small Animal Exploitation. Science 283:190 - 194.


The Walker et al paper shows empirical patterns in growth and body size among contemporary hunter-gatherer populations. Pay close attention to the general relationships that this paper demonstrates. In parts of the paper there are a lot of statistics that you may or may not be familiar with. As always, do not get bogged down in the technical language. Do your best and maybe google some or all of the terms you aren't familiar with (if there are any). The discussion section of the paper is quite lucid and does a good job of clarifying the implications of the statistics in the paper.

The Palkovacs paper takes a life history approach to explaining the patterned changes in body size that are described by the Island Rule. To the best of my knowledge this is the only life history approach to the problem that has been published. What do you think of the approach taken in this paper? Is it more complicated than it needs to be? Is there anything missing or is there any extraneous detail? Remember the definition of a reaction norm that we mentioned briefly in class on Thursday. A given gene doesn't necessary code for a single static phenotype. Phenotypes can change depending on the conditions of the external environment. This capacity for change is a reaction norm. Some examples include changes in skin color in response to sun exposure or changes in growth rate in response to energy availability.

The paper by Stiner and colleagues is an archaeological analysis of data that might seem removed from what we've been talking about. But when do we see changes in human diet and what types of changes occur? What might cause these changes? What was going on with human body size at this time? Do any of the patterns we see in Stiner et al. relate to what we are learning about body size change in Walker et al. and from Palkovacs?

We have also posted a few optional papers showing that some of the same tradeoffs we've been discussing in the contexts of the Island Rule and among hunter-gatherer growth patterns are present in industrial economies. These papers are really exciting and I hope you can check some of them out, especially now that you're armed with some theoretical tools to put these patterns into a larger context. (For readers outside the class - note that you can access these papers by following the directions and hotlink on the sidebar to the right where it says 'ereserves').

Please let me know or post a comment as soon as you can if there are questions about terms and/or concepts in these papers.

I hope you all have great weekends.
Oskar

Island Rule Blog

The Island Rule:
A generalized trend of changes that occur when species from large land masses colonize islands. Larger colonizing species often form dwarfed populations and small species generally become larger. On the island, space is more limiting and the number of species present is relatively lower. These very general differences lead to changes in evolutionary pressures on the organism, although individual islands and circumstances may have idiosyncratic differences as well. Plants also have insular trends, however, that may related to similar pressures as those which cause the changes seen in mammals. Plants that are herbaceous annuals on the mainland often become tree-like perennials on islands. Additionally, birds and insects have been known to loose their ability to fly after colonizing islands.

We are reading two papers about the island rule.
Lomolino, M. V.
2005 Body size evolution in insular vertebrates: generality of the island rule. Journal of Biogeography 32:1683 - 1699.

Palkovacs, E. P.
2003 Explaining adaptive shifts in body size on islands: a life history approach. Oikos 103:37 - 44.


The Lomolino paper was optional for week 4 but the Palkovacs paper is required for week 5.

Lomolino's abstract:
"Aim My goals here are to (1) assess the generality of the island rule – the graded
trend from gigantism in small species to dwarfism in larger species – for
mammals and other terrestrial vertebrates on islands and island-like ecosystems;
(2) explore some related patterns of body size variation in insular vertebrates, in
particular variation in body size as a function of island area and isolation; (3)
offer causal explanations for these patterns; and (4) identify promising areas for
future studies on body size evolution in insular vertebrates.
Location Oceanic and near-shore archipelagos, and island-like ecosystems
world-wide.
Methods Body size measurements of insular vertebrates (non-volant mammals,
bats, birds, snakes and turtles) were obtained from the literature, and then
regression analyses were conducted to test whether body size of insular
populations varies as a function of body size of the species on the mainland
(the island rule) and with characteristics of the islands (i.e. island isolation and
area).
Results The island rule appears to be a general phenomenon both with
mammalian orders (and to some degree within families and particular
subfamilies) as well as across the species groups studied, including non-volant
mammals, bats, passerine birds, snakes and turtles. In addition, body size of
numerous species in these classes of vertebrates varies significantly with island
isolation and island area.
Main conclusions The patterns observed here – the island rule and the
tendency for body size among populations of particular species to vary with
characteristics of the islands – are actually distinct and scale-dependent
phenomena. Patterns within archipelagos reflect the influence of island
isolation and area on selective pressures (immigration filters, resource
limitation, and intra- and interspecific interactions) within particular species.
These patterns contribute to variation about the general trend referred to as the
island rule, not the signal for that more general, large-scale pattern. The island
rule itself is an emergent pattern resulting from a combination of selective forces
whose importance and influence on insular populations vary in a predictable
manner along a gradient from relatively small to large species. As a result, body
size of insular species tends to converge on a size that is optimal, or fundamental,
for a particular bau plan and ecological strategy."

Why study the Island Rule in human macroecology?
there are many reasons, but a few include the following:
- Understanding the nature and causes of the Island Rule provides insight into really general features of mammalian evolution. With this comes the potential to generalize the insights to other cases where body size changes. This helps us understand selection in general in addition to life history evolution because of the strong interaction between life history attributes and body size.
- The variables that seem most important for understand the Island Rule include resource availability, predation pressure and/or mortality, population density, and competition. On islands we might be able to isolate, more or less, the sustained effects of changes in these key ecological variables. We want to understand how these variables have affected human evolution via changes in range expansion and body size, among others.
- Something we did not talk about in class is that we also need to understand how humans affect the other species. It is often difficult to link human activities like predation and land disturbance to the disappearance of other species. Yet when humans prey on an animal, they are influencing its mortality rate and when humans disturb habitats they may be altering resource availability via effective territory size. Therefore, there is an important link between two of the important variables in the island rule, resource availability and predation pressure, that might help us understand how humans alter the demographic features of their prey or other species they interact with. If humans hunt animals or take their eggs (and the like) then they are altering their mortality rates. If they disturb habitats they may be limiting resource availability for certain species.

(I had intended to do a lot more with this blog. I hope this helps clarify and keep us all on the same page.)

One limitation to our understanding of body size changes on islands is that it is not usually approached as a life history problem. We'll talk more about that next week as we read the Palkovacs paper.
Have a good weekend
Oskar

small edits to Blog in response to recent questions

Hi folks,

In response to blogged questions, I added definitions for clinal variation and directional selection to the main posting for this week. And in response to another question, I pasted reference info and a condensed abstract for Pilbeam & Gould, 1974 (mentioned in one of our readings) just below the last definition for the week.

Feel free to ask me if either definition is unclear or for a graphical explanation. See you in class.

Bill

Readings for week 4: variation in human body form

This week we read two papers that show interesting patterns, across space and through time, in the size and shape humans. Here they are:

Morwood M.J., Soejono R.P., Roberts R.G., Sutikna T., Turney C.S.M., Westaway K.E., Rink W.J., Zhao J.x., van den Bergh G.D., Due R.A., Hobbs D.R., Moore M.W., Bird M.I. & Fifield L.K. (2004) Archaeology and age of a new hominin from Flores in eastern Indonesia. Nature, 431, 1087-1091

Ruff, C. 2002. Variation in Human Body Size and Shape. Annual Review of Anthropology 31:211 - 232.

There is some technical language in each paper. For instance, the Ruff paper discusses some of the methodological issues in estimating stature from skeletal measurements. Don't worry about the specifics here but it is interesting to think about how the lifestyle behind the fossil in question and its geographic location affect its size and how we estimate it. Its also good to think about the details of data gathering for these big picture trends, which are not addressed by a lot of the papers we'll read. The Morwood et al paper has some details about specific dating techniques. I don't plan to discuss these at all - just know that they used a variety of techniques to determine the range of dates that bound the geological context of the finds. If you want to understand the specifics of the techniques let me know or try a google search.

Pay special attention to the trends in body size change and the brief mentions of their proposed explanations. Note that even though there is not any life history theory here, we know that major shifts in size must be related to shifts in life history characteristics. What sets body size? Why should an organism get bigger or smaller? But the focus of both papers is the range in variation in body size and the 'clinal' patterning we see in time and space.

Some Flores background:
Most of you have probably heard about the Flores finds - the potentially new species of hominid found on the Island of Flores in the Lesser Sunda Islands a few years ago. Its been hotly debated ever since. A lot of researchers do not like the idea that H. floresiensis is a dwarfed form of H. erectus, but this was the first proposed explanation and still represents an important and current study with implications for human biogeographic patterns of size, colonization, evolution, and so on. It is often referred to as the 'hobbit' because of its very small size.

This is a figure from a news and views piece in Nature by Lahr and Foley that helps place the Flores finds in the context of our evolutionary tree (assuming you accept the finds as that of a new species).

Nature Published online: 27 October 2004; doi:10.1038/4311043a Human evolution writ small Marta Mirazon Lahr & Robert Foley

Figure 1. Homo floresiensis in the context of the evolution and dispersal of the genus Homo. a, The new species as part of the Asian dispersals of the descendants of H. ergaster and H. erectus, with an outline of the descent of other Homo species provided for context. b, The evolutionary history of Homo is becoming increasingly complex as new species are discovered. Homo floresiensis (left) is believed1 to be a long-term, isolated descendant of Javanese H. erectus, but it could be a recent divergence. 1, H. ergaster/African erectus; 2, georgicus; 3, Javanese and Chinese erectus; 4, antecessor; 5, cepranensis; 6, heidelbergensis; 7, helmei; 8, neanderthalensis; 9, sapiens; 10, floresiensis. Solid lines show probable evolutionary relationships; dashed lines, possible alternatives.

Here you see how floresiensis compares to other hominin species with respect to brain and body size (from the same article by Lahr and Foley - yes the same Foley that wrote the paper we read in week 2).

Human evolution writ small Marta Mirazon Lahr & Robert Foley

Figure 2. The relative brain and body size of H. floresiensis. The dimensions of the skull and skeleton (LB1) described by Brown et al. fall well outside the extremes seen in H. sapiens and the 'erectines' (a range of hominin species, of which H. erectus is the most familiar). LB1 is closer in size to, but even smaller than, the australopithecines, of which the best known example is Lucy. On various anatomical grounds, however, Brown et al. believe that LB1 represents a dwarfed H. erectus.

There is a vast amount of discussion of the Flores finds on the John Hawks blog as well.


Terms and concepts:

clinal variation – [in response to Steven’s question] within a given species or related group of species (also called a taxon), gradual variation in a trait along some geographic axis. For example, the gradual decrease in the size of rabbit ears with increasing latitude is a clinal variation. Another example is a gradual change in some plant’s flower color from red to reddish pink to pink to light pink to white over the plant’s range. If instead the plant just had red flowers in one area and white in another, with no “mixtures” in between, you’d say the plant exhibits “discrete variation” in flower color.

directional selection – [in response to Dennis’s comment] selection toward an extreme version of a trait. For example, a population of rabbits in which small-eared individuals are most likely to survive and reproduce is undergoing directional selection for ear size. Think of direction selection shifting the bell curve for some trait toward one end or the other.

Sexual dimorphism: difference between the sexes. For height this is often expressed as average male size divided by average female size (or vice versa). It is often thought that higher levels of dimorphism reflect important behavioral and mating characteristics. If males compete for access to groups of females, they may have to be very large to fight off rival males. When females and males are closer to the same size it is sometimes considered to indicate a prevalence of monogamy. If so, observing an increasing trend toward lower levels of dimorphism in the hominin fossil record has important implications for social structure and life history. Potentially, when male investment becomes more important, pair-bonds become more stable, and male-male competition over females decreases. This might link to some arguments about slow growing and highly dependent offspring that are key characteristics of the human life history. The grandmother hypothesis that we talked about a few weeks ago is at odds with the view that increased similarity in size between males and females indicates that our species was pair-bonding (stable marriage-like pattern of male-female bonding). The grandmother hypothesis argues that males produce meat from hunting in order to gain access to mates apart from their wives. Essentially, males are actually parasites on the productivity of their wives and their wives' mothers and meat is not really a nutritionally important resource. Please think carefully about interpretations of sexual dimorphism.

stature - height

bi-iliac breadth - this is one of a few measures of human body form mentioned by Ruff. It is the widest distance between the pelvic bones. (the bones that you can feel as your 'hips'). it is measured with a special kind of caliper.

Bergmann's Rule - Mammals and birds tend to be larger at colder temperatures and higher latitudes.

Allen's Rule - Warm-blooded animals tend to have shorter limbs in colder climates.

secular trend - a trend that continues over large periods of time. Often meant to mean directional change.

clinal variation - Gradual continuous change in an observable physical (morphological) trait across space and within the range of some group of related organisms. The observed change is usually related to some environmental feature.

stegodon - an extinct species of elephant. Dwarf stegodons were found near the Flores hominids; in the same levels and close by. A common trend is that large mammals that colonize become much smaller. It has been hypothesized that this process, insular dwarfism, may explain the small hominids on Flores.

what do we call ourselves? There is a lot of nomenclature in the readings this week. Keep in mind that the evolutionary tree for primates is getting reorganized all the time and often this requires using new terms or changing the definition of existing terms. For the most part - hominid refers to all great apes. This includes fossil relatives like australopithicines and living species like chimps, orangutans, and gorillas. Note that for the sake of confusion some authors used hominid to refer to only bipedal ancestors. Hominin is used by Ruff to mean humans and their ancestors (homo sapiens and the extinct varieties of homo that preceded us) but slightly different definitions exist as well.


Condensed abstract of Pilbeam & Gould, 1974, in response to blog query:

Pilbeam, D. and Gould, S.J. 1974. Size and scaling in human evolution. Science 186: 892-901.

“Our general conclusion is simply stated: many lineages display phyletic size increase; allometric changes almost always accompany increase in body size. We cannot judge adaptation until we separate such changes into those required by increasing size and those serving as special adaptations to changing environments.
In our view, the three australopithecines are, in a number of features, scaled variants of the "same" animal. In these characters, A. africanus is no more "advanced" than the larger, more robust forms.
The fossil hominids of Africa fall into two major groupings. One probable lineage, the australopithecines, apparently became extinct without issue; the other evolved to modern humans. Both groups displayed steady increase in body size. We consider quantitatively two key characters of the hominid skull: cranial capacity and cheek tooth size. The variables are allometrically related to body size in both lineages.”

Helen Davis, the ghost student, writes about her human health project in South Africa

Dear class,
Did you know we have another student that you have not yet met? Why, you ask? Because she is currently working with the People's Health Movement of South Africa on an important project aimed at lowering the rate of fetal alcohol syndrome in two South African rural communities. Here's someone out there trying to make a difference in the world of human ecology by doing some applied work and Helen's been nice enough to write us a little blog post about her efforts there that I think you will all find very interesting. A couple of articles about fetal alcohol syndrome that are related to the project can be found here and here. Helen will join the class in person later this month.

That's enough from me - here's a brief synopsis of Helen's work down there that she submitted via email:

My research thus far has focused on the substantive role of health and ecology on juvenile development. Specifically, I am interested in the extent to which health, structural, and cultural constraints impact variation in juvenile development and cognitive performance. Over the last couple of years my interests have broadened to include the social and practical applications of this research. Specifically, I am interested in assessing and documenting the obstacles transitioning populations face as they acculturate into a market economy—the ultimate goal being to develop culturally appropriate public health and education programs.

The University of Cape Town in South Africa is a unique research institution which uses Anthropology, Public Health, Human Rights and Medicine to combat many issues that have come to light since the end of apartheid (such as battling the world’s highest rates of HIV/AIDS and Fetal Alcohol Syndrome, as well as growing health issues in children due to maternal exposure to toxins and pesticides while pregnant). I am currently working on two projects here at UCT in order to learn how this program approaches the health concerns and issues facing many transitioning and/or disenfranchised populations.

One of the projects is looking at Fetal Alcohol Syndrome (FAS) and possible methods of intervention. FAS is an entirely preventable congenital anomaly manifesting as abnormal development, such as cognitive and personality impairments, as well as physical deformities in children, is an issue of great concern and debate within South Africa. Recognizing and recording how these situations have arisen, their repercussions and to develop preventative methods for future generations is overarching goal of this project, which is funded by the Center for Disease Control (CDC).

Alcoholism among traditional populations and within developing countries has been attributed to poverty, exploitation and a lack of education. Within South Africa, historical exploitative labor practices under apartheid—known as the DOP system—paid laborers and farm workers in the form of alcohol rations. As a result alcohol dependency and problem drinking is widespread in farming communities in the Western Cape Province of South Africa, and the region is host to the highest rate of FAS in the world (studies estimate that 4 to 6% of school-going age children in rural areas of the Western Cape have the full-blown FAS syndrome). The consequence of FAS for families, communities and society at large are enormous.

As a student working with this research program I have been granted the opportunity to work with the development, implementation and evaluation of interventions that may reduce the risk of alcohol-exposed pregnancies, and are specific to the individual at risk, service providers and the general community. Three levels of interventions are currently being evaluated. Since there is little evidence of the effectiveness of different prevention approaches, they must be determined through carefully controlled evaluation studies.

This study is taking place within 2 distinct sites: City of Tshwane, in Gauteng, and the West Coast of the Western Cape. I work solely with the project in the Western Cape. If anyone wants more information about the project itself or the target population I would be glad to provide it; however, I feel I have probably already bored everyone to tears.

Niche Construction

We've had a lot of questions and comments about niche construction so I thought some additional information might be worth while. The authors of the book that Terrell cites in his paper have a pretty nice website that I recommend checking out. Here's an excerpt that explains how they think of niche construction:

"Niche construction is the process whereby organisms, through their activities and choices, modify their own and each other's niches. By transforming natural selection pressures, niche construction generates feedback in evolution, on a scale hitherto underestimated, and in a manner that alters the evolutionary dynamic. Niche construction also plays a critical role in ecology, where it supports ecosystem engineering and part regulates the flow of energy and nutrients through ecosystems. We are developing a new approach to evolution - one that treats niche construction as a fundamental evolutionary process in its own right. We call it extended evolutionary theory. "

If you are interested in this topic I highly recommend spending some time on the website. Also note that they have posted a pdf of the first chapter of their book, which you can get by clicking here. Its really an interesting read. They make the point that we are missing a fundamental process of evolution if we don't specifically pay attention to how the feedbacks between organism and environment alter selective pressures. In short, they argue that niche selection changes the way we view the processes of evolution. It of course has rather large implications for humans as we are seemingly big-time niche constructors.

Best,
Oskar

Genome sequence of individual human

Here's a cool paper hot off the presses at PL0S Biology:

The Diploid Genome Sequence of an Individual Human

It shows how diverse a single genome can be by comparison with other samples and suggests that, in a nutshell, humans might be slightly less genetically homogeneous than previously thought.

One weekly blogged question can be a comment instead

Odds are some of your ideas on and from the readings are more comments than questions, so feel free to make one of your weekly blog entries a comment or reaction to the readings or to questions in our posted blogs.

Bill

Society for Human Ecology, International Conference

Our friends over at Human Ecology Forum have posted a reminder that the annual meetings for the Society for Human Ecology are approaching. This year they will be held in Rio de Janeiro from October 4 - 7. A few of you have asked about conference information - follow the links to see what the society for human ecology is up to and to get a better feel for the kinds of topics they address.
best,
O

More thoughts on human biogeography

Here are some thoughts and questions to accompany your reading and thinking about human biogeography, the topic of our third week. I’ve defined some vocabulary words at the end.

Chapter 1 of Lomolino et al. contains an excellent discussion of the philosophy of science generally and biogeography specifically. It’s well worth reading. Terrell’s article is nicely historical and provides both good information and provocative ideas.

First familiarize yourself with biogeography as a topic and as a science. Like other scientific fields, biogeography starts with the relationship between pattern and process. What are some examples from human ecology not covered in the readings? How might you go about investigating them? For example, how does “isolation by distance” affect human ecology? How might you “test” for human uniqueness in this respect?

Lomolino et al. note that “H. sapiens possessed an unrivaled ability to adapt to, modify, and eventually dominate a variety of environments.” What are some implications of such “niche contruction” ability, as Terrell would say? Terrell also stressed the importance of environmental factors in structuring human biogeography. How might one begin to tease such distinctions apart?

How might the development of key technologies, as with seafaring vessels, parallel hypotheses about the drivers and pace of biological evolution? (Hint: look for info on John Maynard Smith’s ideas about evolutionary innovations and transitions) , This perspective might be useful for examining modern aspects of human ecology.

Terrell notes that “Although the basic ingredients of what might be called human biogeography have long been part of academic life, these elements have not become a prominent feature of modern advances in ecology and evolution.” From what you know, do you agree?

Vocabulary

admixture – mixture of genetically different groups

biogeography – “the science that attempts to document and understand spatial patterns of biodiversity”. Biogeographers explore how biodiversity varies over the Earth and underlying reasons for this variation. Biogeography is typically a comparative and observational science rather than an experimental one.

island biogeography, equilibrium theory of (Lomolino p. 734, 2nd to last paragraph)– idea that the number of species on an island “represents a dynamic equilibrium between opposing rates of immigration and extinction.” It’s an “equilibrium” because new arrivals are offset by extinctions, and it’s “dynamic” because the precise makeup of species changes over time. Ecologists Robert MacArthur & E.O. Wilson proposed it in 1967.

mesic (p. 730, paragraph 2, Lomolino) – relatively moist, with relatively stable temperatures

taxon cycle (Lomolino p. 738 bottom) – a “cycle” of colonization, evolved specialization, and eventual replacement by new generalized colonists. E.O. Wilson proposed the idea to explain patterns in the Melanesian ant fauna, and Jared Diamond extended it to humans

vicariance (p. 730, end of paragraph 1, Lomolino) – geographic separation due to physical events, such as tectonic shifts, rather than active dispersal of organisms

xeric (p. 730, paragraph 2, Lomolino) – relatively dry

Readings for Week 3: Humans and biogeography

This week we are reading an article and a couple of sections from a prominent text book in biogeography.

Lomolino, Riddle, and Brown. 2005. Biogeography 3rd Edition, Sinauer Press. pages 3 - 12 and 728 - 743.

Terrell, J. E. 2006. Human biogeography: evidence of our place in nature. Journal of Biogeography 33:2088-2098.


The excerpts from the biogeography text book define the field of biogeography and give good examples of human biogeographic patterns. It also contains good background information on human colonization of the world.

The Terrel paper gives good background for the valuable contributions that biogeography can make to the social sciences. It also provides a philosophical discussion for how perspectives on the human place in nature have changed through time and by discipline. I contacted Dr. Terrell to see if he would be willing to chime in to our blog discussions of his paper. He responded with interest but is traveling next week. As an alternative I will email him a few of our questions and we can post his responses. So please think of very good discussion questions that you can ask to the author directly.