Quantity/quality offspring tradeoff in humans and other primates

The following article is available online in firstcite with the Proceedings of the Royal Society B.

Title: The tradeoff between number and size of offspring in humans and other primates

Abstract: Life-history theory posits a fundamental trade-off between number and size of offspring that structures the variability in parental investment across and within species. We investigate this ‘quantity–quality’ trade-off across primates and present evidence that a similar trade-off is also found across natural-fertility human societies. Restating the classic Smith–Fretwell model in terms of allometric scaling of resource supply and offspring investment predicts an inverse scaling relation between birth rate and offspring size and a −¼ power scaling between birth rate and body size. We show that these theoretically predicted relationships, in particular the inverse scaling between number and size of offspring, tend to hold across increasingly finer scales of analyses (i.e. from mammals to primates to apes to humans). The advantage of this approach is that the quantity–quality trade-off in humans is placed into a general framework of parental investment that follows directly from first principles of energetic allocation.

Authors: Robert Walker, Michael Gurven, Oskar Burger, Marcus Hamilton

I have a biased perspective but I think this is a really good paper. It combines the classic model of the quantity/quality tradeoff in life history theory developed by Smith and Fretwell with a recent model by Charnov and Ernest (citations below).
The Smith-Fretwell model basically says that the relative cost of a kid C is the total energy budget mom has to put toward making kids R divided by the number of kids she has N. so C = R/N. This also means that the number of kids then is given by N = R/C. This is a pretty straight forward model that works well. So the higher the cost of an average kid to an average mother in a species or population the fewer kids the average mom will have. We know from life history theory that mom's energy budget R is a function of her mass and that a 3/4 power allometry of body mass is a pretty reasonable estimate for this energy budget. We also know that a reasonable estimate of the cost of a kid seems to be mass at weaning, which is a linear function of mom's mass - about .3M among mammals where M is mom's mass. This means that on average mammal offspring are dependent on their moms for energy until they are about 1/3 her size (Charnov 1993 and others). Anyway, these two observations can be placed into the Smith-Fretwell model to predict another well-known allometric relationship, the -1/4 power scaling of fertility rate with body mass. This happens because R is proportional to M^3/4 and C is proportional to M^1 so we get that N can be predicted by M^3/4 divided by M^1 which gives us M^-1/4. Or we can use these same expressions to look at the relationship between the number and size of offspring, which is predicted to be an inverse relationship (N/R = 1/C ~ M^-1). Our analysis demonstrates that the theory predicts the actual empirical trends in humans and primates.

If this is kind of thing is new to you just realize that when we look for patterns across large numbers of species - like all mammals or all birds - we find these really consistent relationships where a lot of important traits seem to be largely constrained (or at least well-predicted) by the average adult mass of the species. Three of these traits used here are metabolic rate, which is taken to be energy budget, the size of the offspring when its independent from its mom (important because that's when the mom can start making new kids if she wants so its a key constraint on fertility), and these two predict another - that fertility rate is slower with larger animals than with smaller ones.

We need to keep in mind that mass at weaning is generally a good proxy for the measure we are really interested in which the energetic cost of the offspring to the mother. For primates and in humans in particular, however, this may not be a good approximation. Human mothers invest much more in their offspring as human kids are often dependent long after they are weaned.
We take this into account by looking at mass of the offspring at ages older than the typical age at weaning and find that the model works better as a result. So this basic prediction of life history theory, that a tradeoff exists between the number and size of offspring, is met with data on human groups (natural fertility, small-scale populations) and among primates. There are some other points to the paper as well and we hope people find it interesting and that it provokes further research in this area. comments welcome of course.

I'll post a stable link to the pdf of the paper as soon as I can but something is wacky with UNM's server so I can't right now. [Ok, here's a link to a pdf of the paper.] If you are on a computer that has access to the proceedings of the royal society then you should be able to get it here.

best,
Oskar



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Charnov, E.L. & Ernest, S.K.M. 2006 The offspring-size/clutch-size trade-off in mammals. Am. Nat. 167, 578–582, (doi:10.1086/501141).

Charnov, E.L. 1993 Life history invariants: some explorations of symmetry in evolutionary ecology. Oxford, UK: Oxford University Press.

Smith, C.C. & Fretwell, S.D. 1974 The optimal balance between number and size of offspring. Am. Nat. 108, 499–506, (doi:10.1086/282929).

"Evidence for declines in human population densities during the early Upper Paleolithic in Western Europe"

In PNAS's first issue of the New Year, Eugene Morin elegantly combines a macroecological approach with archaeological data to investigate forager ecology and the evolution of modern humans. Amongst other things, Eugene Morin finds a strong correlation between hunter-gatherer population density and mammalian species richness (see Morin's figure pasted on the right). Please post any comments you have of this paper on the blog.

"Evidence for declines in human population densities during the early Upper Paleolithic in Western Europe", 2008, PNAS, 105, pp. 48-53.

Abstract

"In western Europe, the Middle to Upper Paleolithic (M/UP) transition, dated between 35,000 and
40,000 radiocarbon years, corresponded to a period of major human biological and cultural changes. However, information on human population densities is scarce for that period. New faunal data from the high-resolution record of Saint-Ce´ saire, France, indicate an episode of significant climatic deterioration during the early Upper Paleolithic (EUP), which also was associated with a reduction in mammalian species diversity. High correlations between ethnographic data and mammalian species diversity suggest that this shift decreased human population densities. Reliance on reindeer (Rangifer tarandus), a highly fluctuating resource, would also have promoted declines in human population densities. These data suggest that the EUP represented for humans a period of significant niche contraction in western Europe. In this context, the possibility that a modern human expansion occurred in this region seems low. Instead, it is suggested that population bottlenecks, genetic drift, and gene flow prevailed over human population replacement as mechanisms of evolution in humans during the EUP."

Darwin2009: The Beagle Project

I just learned about the Beagle Project from John Hawkes' blog.
As the page for the Beagle Project explains:
"2009 is one of the most significant anniversary years in science: it marks the 200th anniversary of the birth of Charles Darwin (12 February 1809), and the 150th anniversary of the publication of his book On the Origin of Species by Means of Natural Selection."

and then,

"Our contribution to this [celebration of this great anniversary] will be to build a sailing replica of HMS Beagle, the ship on which Darwin circumnavigated the globe between 1831 and 1836. It was during the shore expeditions he made from the Beagle that he collected the specimens which would later inspire the theory of Natural Selection and the Origin of Species.

The replica HMS Beagle will be launched in 2009 and will spend the year opening its decks to the public, teachers and scientists and supporting the Darwin200 celebrations."

So they are going to build a replica Beagle and then sail over the same ground that Darwin covered when he participated on this epic voyage. They are going to bring modern equipment and do a number of inspired projects along the way.

What a phenomenal sounding adventure. All I can say is 'take me take me!!'. Don't you think they need an archaeologist? Especially one that is interested in things like island biogeography, primate life history variation, foraging behavior, conservation biology, scaling/metabolic theory, natural history in general, and oh of course -human macroecology- and who is tons of fun to work with? Sign me up. Yeah, there's no way this is a complete voyage without a human macroecologist. Somebody please convince them for me.


Best,
Oskar

Special Feature: Foraging with Charnov

This semester I'll be taking a 1 hour seminar from Dr. Ric Charnov that meets every Friday, in which we'll be going through a new book on Foraging theory that just came out a few months ago. (also available at Amazon).

Foraging: Behavior and Ecology (Paperback)
by David W. Stephens (Editor), Joel S. Brown (Editor), Ronald C. Ydenberg (Editor)



The book contains 14 chapters and we'll be going through each one sequentially, one per week.
Each week after class I'll write a short blog about the chapter and try to summarize any highlight's from our class discussion. I really hope some of you out there who are interested in foraging will read along and chime in on the blog. It should be a good way to get up to date on this challenging and always rapidly expanding field.

I probably wouldn't argue that all things foraging theory are necessarily part of what we call human macroecology but foraging behaviors and the models used to understand them are fundamental to a vast range of ecological and evolutionary questions. Moreover, foraging behaviors may often be part of the rule sets generating complex emergent social/group level/population patterns. That is, they may be part of the simple rules of interaction that generate emergent macroecological trends.

Anyway, starting next Friday for all weeks of the semester except springbreak there will hopefully be a blog about the chapter we discussed that week. Next week we start with chapter 1 ; Foraging: an overview, by R. C. Ydenberg, J. S. Brown, and D. W. Stephens.
see you then,
Oskar

"Wallace should hang" ?

The New York Times has just published an interesting opinion piece called "Wallace should Hang" by evolutionary biologist and science writer Olivia Judson in recognition of Alfred Russel Wallace. Wallace was an independent 'discoverer' of the process of evolution by natural selection and a founding father of the field of biogeography. He often plays the role of an unsung hero and his contribution to the field seems to be misscharacterized in many settings. He anticipated many of the important issues of and processes of biogeography and was a great thinker although he had some nuances that the story does a good job of presenting. Check out this interesting read!

A couple hits from the blog ('osphere)

Here's some fun reading:
Anthropology.net has this story about recent work regarding population declines in the Upper Paleolithic.

Freakonomics has an interesting post about the recent hubbub over California's emission reduction program getting blocked by the federal government. And it includes links/ref to a story that attempts to break down the economics behind California's plan. They argue that the costs of their plan have been severely under-estimated and that if California moved forward with it, it would contribute to the state's financial woes. I have to admit that I wish the study were wrong because I like the idea of the states taking the lead on a very lackluster federal government on issues like this. But it is of course a complex matter and we shouldn't endorse any plan that sounds good... We should pay close attention to this and other potential conflicts between state governments and the Feds/EPA on issues of sustainability, emission reduction/energy-use/recycling and the like.

And lastly - are you left or right brained? I see this thing going one way and one way only - I can't imagine it going counter-clockwise. See for yourself.

Oskar

Course wrap-up: its over now...

Well, the semester is long done now. The papers are in, grades are out, and we've gone on to other things as far as the class goes. Overall, it was a great semester (er at least I thought so...) and we ventured over a lot of territory in the literature. The students were fantastic and taught the instructors a great deal. Thanks. We appreciate everyone's hard work.

The blog has been a bit slow lately but hopefully will pick up steam again here soon as I recover from my xmas break coma. This blog will change a little bit as it won't be specifically a course resource in the following semester, but it will remain active as a hotbed for information, news, and discussion on human macroecology (and other broadly related themes of course). And you all know I'd love to have a few more consistent contributors... I hope those of you who took the class and any who just stumbled onto this blog will continue to check in regularly.

We also really enjoyed doing the 'end oral dialogs.' (Each student met with the instructors for an hour long conversation about the semester during finals week). While a full day of these rendered Bill, Jordan, and I nearly brain dead and certainly less-able-than-usual to speak in complete sentences, we got a lot out of finding out what people really focused on during the semester - and what they retained as the salient themes. Pretty unanimously people liked the structure of the class - having a blog as a resource - focusing on discussion of recent papers.
Most folks really liked adopting the concepts of emergence and the theoretical toolkit of life history theory into human ecology. We did not get a clear consensus for things like the favorite paper but the content of Bettencourt et al (2007 in PNAS) and Moses and Brown (2003 in ecol letters(this link is to a pdf)) sure seemed to stay with people and leave them thinking. These papers are definitely thought provoking and provide theoretical frameworks and findings that should be widely contemplated and discussed. The classic paper by Leslie White (1943) also seemed to leave a lasting impression. Other frequently mentioned papers included those from the week on extinctions and the system dynamics approaches outlines in weeks 10 and 11 (especially papers by Tainter and Holling). Life history theory in general seemed widely appreciated as well.

We hope that as people move forward into different areas that they'll retain some of the approach to science we outlined and maintain a skeptical and analytical view when approaching claims of human uniqueness. We also hope they'll consider those very large-scale patterns and the mechanisms that underlie them - of course not to replace of microecological studies but to compliment them and extend their findings.

More soon.

Best wishes everyone. Thanks again for a great semester.

Happy New Year.

Oskar

Human Capital Vol. 1, N. 1: First issue of a new journal

University of Chicago Journals has recently published the first issue of the new journal - Human Capital . This journal is based on a series of theoretical developments in economics beginning about 40 years ago leading to what today is called human capital theory. While it dates back to some classic theorists it is probably most closely associated with economists Gary Becker and Theodore Schultz. Students of human evolution should be familiar with the concept from its role in embodied capital theory, which has been used by Hilly Kaplan and colleagues to explain the coevolution of intelligence, long lifespan, dependent offspring, and complex foraging niche that has characterized primate diversification in general and especially the evolution of the human life course and adaptive niche (a pdf of one of the papers on this can be found here).

All of the articles in this inaugural issue look really interesting and blog worthy, so I'm just going to post titles and abstracts so that they are on your radar. It looks like it should be a really interesting journal to watch and I look forward to taking in some of these papers during vacation.
The first paper is by Isaac Ehrlich and Kevin M. Murphy and explains why a seperate journal of human capital is necessary. It gives a nice explanation for the rationale of human capital theory and its historical development.

The rest of the papers in the journal are as follows:

Education and Consumption: The Effects of Education in the Household Compared to the Marketplace

Gary S. Becker and

Kevin M. Murphy

University of Chicago and Hoover Institution

This article considers various differences between the effects of education in the marketplace and households. It shows that the household sector rewards skills that are useful at the many tasks that household members must execute, whereas the marketplace rewards skill at specialized tasks. In addition, increased supplies of more educated persons reduce returns to education in the marketplace, whereas if anything, increased supplies raise household returns to education. The greater demand over 40 years for household and market skills may have raised returns to education in households compared to those in the market sector.

***

The Changing Role of Family Income and Ability in Determining Educational Achievement

Philippe Belley

University of Western Ontario

Lance Lochner

University of Western Ontario and National Bureau of Economic Research


We use the National Longitudinal Survey of Youth 1979 and 1997 cohorts to estimate the effects of ability and family income on educational attainment in the early 1980s and early 2000s. The effects of family income on college attendance increase substantially over this period. Cognitive ability strongly affects schooling outcomes in both periods. We develop an educational choice model that incorporates both borrowing constraints and a “consumption value” of schooling. The model cannot explain the rising effects of family income on college attendance in response to rising costs and returns to college without appealing to borrowing constraints.

***

The Production of Cognitive Achievement in Children: Home, School, and Racial Test Score Gaps

Petra E. Todd and

Kenneth I. Wolpin

University of Pennsylvania


This paper studies the determinants of children’s scores on tests of cognitive achievement in math and reading. Using rich longitudinal data on test scores, home environments, and schools, we implement alternative specifications for the cognitive achievement production function that allow achievement to depend on the entire history of lagged home and school inputs as well as on parents’ ability and unobserved endowments. We use cross‐validation methods to select among competing specifications and find support for a variant of a value‐added model of the production function augmented to include information on lagged inputs. Using this specification, we study the sources of test score gaps between black, white, and Hispanic children. The estimated model captures key patterns in the data, such as the widening of minority‐white test score gaps with age and differences in the gap pattern between Hispanics and blacks. We find that differences in mother’s “ability,” as measured by AFQT, account for about half of the test score gap. Home inputs also account for a significant proportion. Equalizing home inputs at the average levels of white children would close the black‐white and the Hispanic‐white test score gaps in math and reading by about 10–20 percent.

***

The Evolution of Income and Fertility Inequalities over the Course of Economic Development: A Human Capital Perspective

Isaac Ehrlich

State University of New York at Buffalo and National Bureau of Economic Research

Jinyoung Kim

Korea University

Using an endogenous‐growth, overlapping‐generations framework in which human capital is the engine of growth, we trace the dynamic evolution of income and fertility distributions and their interdependencies over three endogenous phases of economic development. In our model, heterogeneous families determine fertility and children’s human capital, and generations are linked via parental altruism and social interactions. We derive and test discriminating propositions concerning the dynamic behavior of inequalities in fertility, educational attainments, and three endogenous income inequality measures—family‐income inequality, income‐group inequality, and the Gini coefficient. In this context, we also reexamine the “Kuznets hypothesis” concerning the relation between income growth and inequality.

***

Enjoy!

best wishes,

Oskar

Sociobiology revisited: a new paper by Wilson and Wilson

An interesting review paper about multi-level selection was just made available (forthcomming) in the Quarterly Review of Biology by D S Wilson and E O Wilson. It's an interesting read. Here's the citation info and abstract:

RETHINKING THE THEORETICAL FOUNDATION OF SOCIOBIOLOGY

David Sloan Wilson

Departments of Biology and Anthropology, Binghamton University Binghamton, New York 13902 USA dwilson@binghamton.edu

Edward O. Wilson

Museum of Comparative Zoology, Harvard University Cambridge, Massachusetts 02138 USA

KEYWORDS

altruism, cooperation, eusociality, group selection, human evolution, inclusive fitness theory, kin selection, major transitions, multilevel selection, pluralism, sociobiology

ABSTRACT

Current sociobiology is in theoretical disarray, with a diversity of frameworks that are poorly related to each other. Part of the problem is a reluctance to revisit the pivotal events that took place during the 1960s, including the rejection of group selection and the development of alternative theoretical frameworks to explain the evolution of cooperative and altruistic behaviors. In this article, we take a “back to basics” approach, explaining what group selection is, why its rejection was regarded as so important, and how it has been revived based on a more careful formulation and subsequent research. Multilevel selection theory (including group selection) provides an elegant theoretical foundation for sociobiology in the future, once its turbulent past is appropriately understood.

The Quarterly Review of Biology, December 2007, vol. 82, no. 4

They are careful about defining their terms. Here are some useful definitions:

"sociobiology is the study of social behavior from a biological perspective, group selection is the evolution of traits based on the differential survival and reproduction of groups..."
"From an evolutionary perspective, a behavior can be regarded as social whenever it influences
the fitness of other individuals in addition to the actor."
"Group advantageous traits do increase the fitness of groups, relative to other groups, even if they are selectively neutral or disadvantageous within groups. Total evolutionary change in a
population can be regarded as a final vector made up of two component vectors, within and between-group selection, that often point in different directions."

They make a point that words like 'sociobiology' and 'evolutionary psychology' have become "tainted" due to their negative associations and bad reputations in many fields. This is of course especially true in the social sciences. I have almost never heard an anthropologist use sociobiology in a positive or even neutral context (only very negative - 'oh that stuff - we know better than that') but the vast majority of anthropologists would think of sociology as a field arguing that genes cause every observable trait we might observe - a much more extreme view than that used by its actual practitioners (above in the definitions).
In a similar vein, anything related to 'group selection' carries the connotation of being an automatically naieve argument even in fields where Darwinian analysis is accepted. I am mostly a behavioral ecologist (studying macroecological patterns) and I have been guilty of this. In many cases, arguments about group selection involve people speaking past each other and missing the point, this is why Wilson and Wilson often use the term 'multi-level selection' instead. We can show that altruism is costly to a perfectly self-interested actor but that a group of altruists out-competes a group of selfish social defectors. If we are comparing groups (populations) and focus only on individual-level benefits we may indeed miss part of the picture, but on the other hand the individual does a lot better in the group that doesn't get killed off by the more altruistic group. So the tension between the two views is not always necessary. Wilson and Wilson look at cases like the evolution of eukaryotic cells and argue that group selection must have been present to get the once autonomous entities (prob some form of early bacteria) to cooperate so closely in a tightly knit network of symbiotic mutualisms that they became organelles in the same cell.

So group selection must be common, they argue. Consider this view: "If a trait is locally disadvantageous wherever it occurs, then the only way for it to evolve in the total population is for it to be advantageous at a larger scale." Is altruism really locally disadvantageous though?

Getting back to relationships between groups, if we want to talk about why different populations spread at the expense of others then I think population level fitness measures are necessary and quite uncontroversially logical. George Williams himself proposed measures of population level fitness in his 1966 treatise against the brand of group selection proposed by Wynn-Edwards and others. [One of these measures was population density or size which he thought was not as good as the second measure, the numerical stability of the population through time, but this has much larger data requirements. These discussions are definitely relevant for our discussions of human evolution.] Wilson and Wilson also point out that there is room for multi-level selection in Williams' view, he only underestimated how frequently it could be important.

They are very careful to separate cogent arguments of multilevel selection from those they label naive group selection. The level of selection needs to be appropriate for the analysis being conducted. My feeling is that we can't categorically reject arguments of selection at the level of genes, individuals, families, other groups, maybe even species in some restricted geological cases like the study of mass extinction, and maybe higher levels like ecological network structures. Here's a nice quote they bring to this issue:
"In biological hierarchies that include more than two levels, the general rule is “adaptation at any level requires a process of natural selection at the same level and tends to be undermined by natural selection at lower levels.” All students of evolution need to learn this rule to avoid the errors of naı¨ve group selectionism. Notice that, so far, we are affirming key elements of the consensus that formed in the 1960s."

Humans are used as an example in many cases in the paper.
"The importance of genetic and cultural group selection in human evolution enables our groupish nature to be explained at face value. Of course, within-group selection has only been suppressed,
not entirely eliminated. Thus multilevel selection, not group selection alone, provides a comprehensive framework for understanding human sociality."

There seems little question that understanding how selection may play out at higher levels will be necessary for explaining how anatomically modern humans came to spread and conquer the globe. But we do need to be cautious with how such arguments are invoked.

This paper is extremely well written and thought provoking. I recommend checking it out.
Best,
Oskar

Complex Systems Summer School 2008

The Santa Fe Institute is now looking for applications for next year's complex systems summer school. I attended the international school in Beijing 2005 and loved it (went back the next year as staff). I recommend it for folks interested in complex systems research from any perspective.

Here's the basic information on the school and how to apply (this is just the text of the email they send to alumni to help circulate the announcement):

_____

Complex Systems Summer Schools

Summer 2008

The annual Complex Systems Summer Schools provide an intensive introduction to complex behavior in mathematical, physical, living, and social systems for graduate students and postdoctoral fellows. Schools will be held in Santa Fe, New Mexico and Beijing, China. Applications are now available at http://www.santafe.edu/csss08.html.

Program Details

Santa Fe: June 1-28, 2008 at St John’s College in Santa Fe, New Mexico, USA. Directed by Dan Rockmore, Dartmouth College and Santa Fe Institute (SFI); administered by the Santa Fe Institute (SFI).

Beijing: June 30-July 25, 2008. Sponsored by SFI in cooperation with The Institute of Theoretical Physics, the Chinese Academy of Sciences (CAS). Co-directors: Dr. David P. Feldman, College of the Atlantic and SFI, and Dr. Chen Xiao-song, Institute for Theoretical Physics, CAS.

General Description

The Complex Systems Summer School offers an intensive four-week introduction to complex behavior in mathematical, physical, living, and social systems for graduate students and postdoctoral fellows in the sciences and social sciences. The schools are for participants who want background and hands-on experience to help prepare them to do interdisciplinary research in areas related to complex systems.

Each school consists of an intensive series of lectures, laboratories, and discussion sessions focusing on foundational ideas, tools, and current topics in complex systems research. These include nonlinear dynamics and pattern formation, scaling theory, information theory and computation theory, adaptation and evolution, network structure and dynamics, adaptive computation techniques, computer modeling tools, and specific applications of these core topics to various disciplines. In addition, participants will formulate and carry out team projects related to topics covered in the school.

Further details about topics and faculty at each school will be posted

as they become available.

Eligibility

Applications are welcome from all countries. Participants are expected to attend one school for the full four weeks. All activities will be conducted in English at both schools. No tuition is charged, and some support for housing and travel expenses is available. Enrollment is limited.

Applications are solicited from graduate students and postdoctoral fellows in any discipline. Some background in science and mathematics (including multi-variate calculus and linear algebra) is required. Proficiency in English is also required.

Students should indicate school location preference when applying. Placements may be influenced by restrictions in U.S. foreign visitor policies.

Application Requirements

1. Current resume or CV. Include a clear description of your current educational or professional status, and a list of publications, if any.

2. A statement of your current research interests and comments about why you want to attend the school (suggested length: one to two pages).

3. Two letters of recommendation from scholars who know your work.

How to Apply

Online: Our online application form allows you to submit all of your materials electronically (including a feature which allows your recommenders to upload letters of recommendation directly to your file). We strongly encourage you to apply online to expedite your application.

Postal Mail/Courier: Applications sent via postal mail will also be accepted. Include a cover letter providing your e-mail address and fax number, and specifying whether you wish to be considered for a travel scholarship. (This will not influence the review of your application.) Do not bind your application materials in any manner. Send application materials to:

Summer Schools

Santa Fe Institute

1399 Hyde Park Road

Santa Fe, NM 87501 USA

If applying via post, letters of recommendation may be sent separately to the address above, or included in your application package in sealed envelopes.

DEADLINE

All application materials, including letters of recommendation, must be received at SFI or electronically submitted no later than January 7, 2008.

Women, minorities, and students from developing countries are especially encouraged to apply.

If you have further questions about the Complex Systems Summer Schools, please e-mail goodwin@santafe.edu