Your discussion questions can go as comments to this posting by using the link below. Recall that at least one question should be posted by Monday night at 8:00 pm. You should post two questions during the week. Its up to you if you want to wait until after class on Tuesday to post the second question or post them both at once. Feel free to respond to your classmates questions.
Here is the bibliographic information for this week's papers:
Foley, R.A. 1996. The adaptive legacy of human evolution: A search for the environment of evolutionary adaptedness. Evolutionary Anthropology 4: 194 – 203.
Some comments on why these papers were selected:
Its important to understand the basics of Life History Theory (LHT). Only a minority of anthropologists use LHT but its made major contributions to the field in the last couple decades or so. LHT applications to humans are inherently interdisciplinary because they are anthropologists using biological concepts that ultimately derive from economics, which fits the theme of the course quite well. Most life history traits (life span, age at first reproduction, mortality rate, age at independence, etc) tend to scale allometrically with body size when large samples of organisms are considered, like all mammals. Hence, such traits are candidates for law-like generalizations for ecology that are relevant for humans. These scaling relationships describe emergent evolutionary patterns spanning several orders of magnitude in biological organization. LHT is also tied to some important energetic principles that link to other energy-based theories of evolution.
More pragmatically: we want you to be able to define LHT. What is it and what does it tell us? What traits of the human life history seem different from other mammals? How has life history theory been used to explain these difference in humans and what have we learned about human evolution along the way?
Because humans are all over the globe we won't compare just their geographic distribution to other species as an interesting biogeographic pattern. We might focus on the biogeographic distribution of specific traits - life history traits among them.
Foley and the EEA:
The human life history evolved in a nonindustrial environment. This is the link to the environment of evolutionary adaptedness, or EEA. Note that Foley is critical of the EEA concept but along the way in his critique he presents some very relevant information about human ecology and our evolutionary history. We don't want to spend a lot of time going into why some people like the EEA concept and some people don't. A lot of the differences are semantic and have to do with other conflicts between human behavioral ecology and evolutionary psychology that are beyond the scope of this class (not that we can't discuss them some). Clearly, we have lived in different environments in the past but is it the case that past evolutionary environments may have tuned us for contexts very different from where a lot of humans are today? Think critically about how much we can and can't learn about our evolutionary past via the study of extant foraging populations. Do we have enough 'microscopic' studies of human foragers to see the macroscopic patterns relevant to investigating life history variation and the EEA?
We want to know to what degree patterns in modern behavior that seem somehow out of step with the environment are tied to behaviors that were more clearly adaptive at another time and place. Hence, the EEA concept is important in lots of discussions and is often implicit well outside of evolutionary psychology where it was widely adopted.
Also keep in mind the notion of 'human uniqueness' in the context of these papers.
See you Tuesday,
Oskar
33 comments:
Question #1: Survivorship, irrespective of reproductive effort would be challenging to model. Besides age at first reproduction, and longevity, what other factors should be considered?
1. In what ways does human ecology acknowledge and account for modern selective pressures while operating under the Environment of Evolutionary Adaptedness?
How many hunter-gatherer societies we have nowadays? Are they generally have more offspring the other kinds of societies?
Mortality age, first reproduction age and body size, which is the cause and which is effect?
1. Do organisms without a distinct germ line show constant mortality with age?
2. If people in modern societies aren't maximizing fitness, what, if anything, are they maximizing?
What is the contribution of men to the diet? Foley, 1996, page 195, column 3, line 12.
As societies become more complex and more diverse, how will EEA handle those changes - when is macro too macro? Specifically, if social and ecological conditions become so varied that some societies progress in radically different directions, is it possible to have multiple environments that yield dissimilar evolutionary changes?
If the evolution of modern hunter gatherers occured simultaniously with the dispersal and isolation of differnt human groups, which ultimately causes the great varibality we see among and between human groups, how does the study of modern hunter gatherers operate within the context of the EEA? (See page 202, middle column, in the Foley article)
The Hill and Kaplan article quotes Hamilton (page 404) as indicating that genes that decrease survival odds after reproduction and increase chances of survival prior to reproduction increase in prevalence. Isn't this a bit obvious? Those people who have a higher likelihood of dying before reproducing won't be passing on their genes. And how exactly does this relate to senescence? I got the impression this was a general weakening and increased vulnerability as a person ages, which may not be the same as decreased survival odds.
Foley states that the conditions of the EEA must be hypothesized independent of modern behavior, based on the known pattern of human evolution and prehistory. But, does he present enough evidence to back up his ideas, or is more archeological and genetic evidence needed to remove bias?
Given the diversity of hunter-gather populations both past and present, is it appropriate to apply the EEA and relevant theories to a solitary population given the uniqueness of population histories and local ecology in order to explore their behavioral evolution? e.g. While the Central Australian Aboriginals date back to around 60 kya and established themselves in a unique environment without fear of large terrestrial predation, would they still exhibit retain similar behavioral characteristics developed during the EEA as a similar arid population (Foley cites the Sub-Saharan San)?
On page 399 of Hill and Kaplin, they list three benifits of increased organism size. They also state that increased maintnace cost is a disadvantage of increased size.
What are some other disadvantages of increased organism size? Surely there must be some, because there are a lot of small organisms out there.
howdy all, the readings reminded me of a website I found sometime ago. I thought it might give some a good laugh. http://www.goveg.org/naturalhumandiet.asp
Hill found that the Ache follow the growth equation dW/dT = A*W^0.75, where A=0.23 for males and 0.29 for females.
Why should human growth rates be constrained by current size, if other folks are providing the calories?
If you want a look at an economic life history model, Hillard Kaplan has been working with Canadian economist Arthur Robson for the last several years, and they presented one at the Santa Fe Institute earlier this month, though I found out about it too late to attend myself.
But you can read their paper "Why We Grow Large and then Grow Old: Economics, Biology and Mortality". As a typical economics paper, there's more math than English, so don't say I didn't warn you
Foley (1996) finds it "ironic that one of [evolutionary psychology's] main concepts stresses the constraints on Darwinian selection." Does Foley overestimate the constrain implied by mismatch due to evolutionary novelty? The changes that have come about in the past 10K years are the blink of an eye in evolutionary terms, and I would argue (this argument is surprising to some) that although many of our traits bear the stamp of an environment that no longer applies, we are very rapidly evolving to catch up even now.
To Paul
Through the metabolism theory, we consider that for any age of organisms before their adult age,
Basal Metabolism (BM) =
Maintain Matabolism (MM)+ energy for growth
BM = MM + Em*dm/dt
Em is the energy to creat unit body mass.
Then dm/dt = (BM-MM)/Em
BM and MM are both related to adult body size and current body size.
BM~M^(a-b)*m^b
MM~M^(a-1)*m
Hope it makes sense. ^_^
To Oskar,
When you said that rabbits have shorter... and human beings have longer..., do you compare them with their similar body size organisms or compare them to each other?
Hey Wenyun,
1) I meant to mention this in class today but would you believe that we actually don't know how many hunter gatherers there are in the world today? I thought about trying estimate this but it would be really difficult. There have been many attempts to find average fertility across foraging and agricultural societies. I'd say that good numbers (from my calculations a while back) are about 5.5 - 6.1 kids per mother for foragers and fully agricultural natural fertility populations might go up to 6.2 kids per mother but not much more than that. I don't think that an increase in fertility is the explanation for the exponential-like growth we see in the Holocene, as is commonly stated.
2) Studies have shown that selection acts directly on body size but given how these traits all very with body size I'd say we might not really know.
3) I mean with respect to the average relationship with body size for mammals - residual variation. If rabbits are below the line for size at independence they are above it (across mammals) for fertility rate, growth rate and mortality while are probably below it for lifespan. (the 'line' being the ordinary least square regression of the trait on body size).
Deepta,
This is a good question. What they are pointing out is that some mutations might have negative effects and the genes that have negative effects will get weeded out with time by natural selection but what if the negative effect doesn't happen until later in life, after the individual has reproduced? What if a mutation brings and advantage early in life but a disadvantage later in life? These sorts of things can accumulate with time and hence genetic material that causes deleterious effects only late in life can explain senescence. This is part of a more general point that selection acts more strongly on the early part of life (younger ages), than the later part. Does that make sense?
Fred,
Good point. More evidence is definitely needed. We need more genetics, more behavioral studies, better phylogenies, the whole bit.
Steve,
This is a huge question. (get it, haha). There is a lot written about what sets body size. No doubt more things are small than large but in a lot of cases most things are a little larger than the smallest size. Larger things need larger territories, more food but have fewer predators. If they become specialized they may be more susceptible to extinction. There's a lot of papers on this. Here's a few references:
-Alroy J. (1998) Cope's Rule and the Dynamics of Body Mass Evolution on North American Fossil Mammals. Science, 280, 731 - 733
-Blackburn T.I.M. & Gaston K. (1998) The distribution of mammal body masses. Diversity & Distributions, 4, 121-133
- later chapters in the brown text book from last week.
-Brown J.H., Marquet P.A. & Taper M.L. (1993) Evolution of Body Size: Consequences of an Energetic Definition of Fitness. The American Naturalist, 142, 573 - 584
-Brown J.H. & Nicoletto P.F. (1991) Spatial Scaling of Species Composition: Body Masses of North American Land Mammals. The American Naturalist, 138, 1478-1512
Kelt D.A. (1997) Assembly of local communities: consequences of an optimal body size for the organization of competitively structured communities. Biological Journal of the Linnean Society, 62, 15 - 37
Kozlowski J. & Gawelczyk A.T. (2002) Why are species' body size distributions usually skewed to the right? Functional Ecology, 16, 419-432
and that's just scratching the surface! Its a huge topic in macroecology but that's a great observation.
Are there any studies that look at the differences/changes in life history between free-roaming forager groups versus those who have been confined to a specific plot of land, thus limiting available resources? This type of study may indicate how life-history changes due to the differential resources during the different stages of sedentism and shed more light on the changes see with the demographic transition.
There is such a study and we'll be reading it in a few weeks!
Dan, I almost forgot!
Hilarious!
funny how there's a unique notion of the EEA in that vegan website huh?
Ran into a couple of recent papers in the Economics literature that are interesting and relevant:
Anne Case and Christina Paxson, in their paper "Stature and status: Height, ability, and labor market outcomes">, explain the long-observed relationship between human height (not body size per se) and income by finding that taller people are, on average, smarter. Childhood scores on cognitive tests predict both height and income.
Enrico Spolaore and Romain Wacziarg's "The Diffusion of Development" finds that genetic distance between populations has a strong relationship with income differences. They develop an economic model to explain their empirical results whereby vertically-transmitted genetic and cultural characteristics between generations act as barriers to the horizontal transfer of innovations between diverging populations.
This answers my first question: organisms without a distinct germ line aren't "immortal" either.
This is somewhat off from the overall discussion subject, but it started bugging me as I was reading the Hill and Kaplan paper. On page 408 they say: "Adult pelvic widening,
menarche, and even copulation generally precede birth by several years
(Wood 1994). This “false maturation” may be an example of signaling deception
by females who attempt to extract higher rates of provisioning from males by
mimicking a state of reproductive readiness."
What implication does earlier menarche in girls in the US have for this hypothesis? Menarche seems to be occuring slightly earlier, perhaps due to increased body weight.
(One paper on earlier menarche is Anderson, SE, GE Dallal, and A. Must. 2003. Pediatrics 111:844-850.)
Can predictions be made about how early life environments, including in utero, affect the life history of an individual?
Oscar:
Would it pose much of a problem to give a detailed explanation on the 'ordinary least square regression of traits on body size, and residual variation', in class?
Tangentially, what is the long term contribution of short term interest in particular subjects? It was brought up during discussion that debate flared up about the EEA in the late 1990’s early 2000’s but later waned. From my own reading, a similar pattern of debate was seen around the same time concerning fluctuating asymmetry. Academicians on the peripheries seem attracted to these temporal topics, and given the interdisciplinary viewpoints provided, seem to provide a great deal of insight…until the next big debate comes around of course.
Justin,
There is another good book about the relationship between culture, health and economics that you might find interesting, if you haven't already seen it: Wealth from Health: Linking Social Investments to Earnings in Latin America (ed. by WD Savedoff and TP Schultz; 2000). It was used as a text book for a course a couple of years ago that was co-taught by an anthropologist and economist. I think the book has a nice balance between graphs, data and discussion.
Thanks for the reference, Verity. It sounds interesting and I'll give it a look.
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