Impact through original research
When I began work on my PhD at the University of British Columbia in January 1972, I was advised to spend a year reading and thinking deeply before deciding on the direction I would take in my thesis. I followed that advice, and out of that year of reflection came a 1976 paper in Quarterly Review of Biology on
- life history evolution.
It was the introduction to my thesis proposal; it launched my career; it helped to define a field; and it earned me a Miller Fellowship at Berkeley, where I spent three years enjoying the freedom to read and think broadly (1975-1978). The issues raised in that paper shaped many of my subsequent contributions. How are organisms designed by natural selection to maximize reproductive success in the face of ecological problems? What is the role of phenotypes in evolution? Those two questions have guided much of my work.
While at Berkeley I wrote
My most read, least cited, and possibly - some think- my most helpful contribution.
The data I gathered for my PhD at British Columbia concerned the rapid evolution of life histories in mosquito fish from the time they had been introduced to Hawaii in 1905 up to the time I sampled them in the early 1970's. At Berkeley and in my first academic position - assistant professor at Reed College - I continued this work on mosquito fish. It resulted in two major conclusions:
- Evolution can be very rapid when large populations are subjected to strong selection. This was one of several contributions that changed minds about the tempo of evolution, which had previously been thought to occur on scales of thousands to millions of years. We saw it happening within decades, and soon it would be observed in laboratory experimental evolution on a timescale of months to years. The problem became not how fast can evolution be, but why is it sometimes so slow? The terms of the debate shifted.
- Gene flow can swamp local adaptation, resulting in mal-adaptation of local populations. This early empirical contribution to the consequences of gene flow is now reflected in thinking about evolution in geographically structured populations and meta-populations - very much an ongoing endeavor. We showed that geographic structure had placed major constraints on the rate of adaptation in a local population.
While at Reed I collaborated with a physicist, Richard Crandall, to develop the first predictions of how evolution should shape plastic responses to heterogeneous environments. My work with Crandall on
- predicting optimal reaction norms for age and size at maturity
was further developed with Jacob Koella when I moved to Switzerland in 1983 to take over the directorship of the Zoology Institute at the University of Basel. The 1986 paper with Koella, now seen as a good start but a partial truth, helped to inspire research on the evolutionary significance of developmental plasticity through the 1990's. Its implications for population dynamics and community ecology are still being explored.
In Basel I switched my empirical system from mosquito fish to fruit flies and continued to work on them for the 17 years I spent in Switzerland. In the early years we took a quantitative genetic approach to life history evolution and addressed questions about the constancy of the genetic variance-covariance matrix, constraints on the evolution of phenotypic plasticity, and the controls needed for experiments in which genetically engineered organisms are used to test ideas about the evolution of aging. From that period - roughly 1985-1995 - emerged the following conclusions:
- Phenotypic plasticity can change the sign of a genetic correlation between two traits from positive to negative across environments. Such strong effects were not expected, and their consequences have not yet been fully assimilated by evolutionary theory. At the time, it was widely thought that the genetic variance-covariance matrix was constant across environments. Our work showed that at least sometimes it is not.
- Selection on a trait in one environment substantially shifts its expression in another environment. Falconer had gotten a similar result in mice; in confirming it in flies we gave a result that he had interpreted as part of quantitative genetics new significance for the evolution of phenotypic plasticity in life history traits.
- Both insert position and genetic background have significant interactions with genetic transformation. Therefore, when testing a genetically transformed organism for effects on whole-organism traits, one must measure position and background effects. In doing that, we demonstrated that claims that lifespan could be extended by 30-40% with single-gene transformations were spurious. The lesson appears to have sunk in. Recent work on aging in molecular genetics labs now usually has such controls.
- Traits with greater impact on fitness appear to be more strongly canalized against the genetic perturbations caused by transformation. This was one of the few empirical results at a time when the issue of canalization, buffering, and the robustness of the developmental system was being resurrected after several decades of neglect. Its meaning is not yet clear, for theoretical work is steadily increasing the number of alternative interpretations of canalization.
In 1987 I published the idea of
- selection arenas,
and reviewed the range of situations in which they appear to exist. A selection arena is a selection process that occurs inside an entity that is a unit of selection in its own right at a higher level. Here natural selection has produced an adaptation that uses natural selection to achieve its effect. Since 1987, selection arenas have been discovered sorting oocytes in human ovaries and zygotes in human wombs, and I have discovered that Darwin had the idea in the 1870's.
My later years in Basel - 1993-2000 - were centered around a 7 year long evolutionary experiment on life history evolution and aging done with fruit flies. That experiment
- confirmed a major prediction of life history evolution and the evolutionary theory of aging: an increase in adult mortality selects for increased reproduction early in life and a shorter life.
The change in life span that we observed in flies - 5 days within 100 generations - would correspond in humans to a change in life span of 5 years since the Trojan War. This result inspired one of my graduate students, Martin Ackermann, to do a similar experiment on a bacterium, Caulobacter, that reproduces asexually by asymmetrical division. His work helped to
- settle an important controversy about what kinds of organisms should age.
Martin showed that Caulobacter ages, and its rate of aging responds to an increase in adult mortality by increasing, just as it does in fruit flies. Thus it now appears that any organism that divides asymmetrically must age, and while the rate of aging may evolve more slowly than do other life history traits, it still evolves rapidly enough to measure in the laboratory - more rapidly than had been expected.
Since moving to Yale in 2000, I have published
- a genomic hypothesis for the origin of tradeoffs.
Tradeoffs exist whenever an evolutionary change in one trait that improves fitness is linked to an evolutionary change in another trait that decreases fitness. Tradeoffs are virtually ubiquitous, constrain multitrait evolution, and are key elements of phenotypic design. Their proximate causes remain in many cases mysterious, and by using a genomic approach we may be able more rapidly to identify those proximate causes.
I am currently engaged in analyzing the intensity of selection acting on contemporary human populations.
Impact through books and reviews
I have had as much impact through my books and review articles as I have had through my original research. Here I list the books and most important reviews:
As sole author:
- The evolution of life histories. 1992. Oxford University Press. This, my most influential book to date, was written in a style and at a level that many found accessible and appeared at a time when the subject was starting to attract interest in neighboring disciplines, such as behavioral ecology and physical anthropology.
- Watching, from the edge of extinction. 1999. Yale University Press. My wife, Beverly Peterson Stearns, is first author. We interviewed people around the world on their reactions to watching their study populations or species go extinct. The book won a prize from Women in Communications.
- Evolution: an introduction. 2000 (2nd. Ed. 2005). Oxford University Press. Rolf Hoekstra is second author. This introductory text aims to move the teaching of evolution earlier in the undergraduate curriculum by presenting key issues clearly and concisely while holding mathematics and population genetics to the necessary minimum. It has sold well.
- The evolution of sex and its consequences. 1987. Birkhaeuser, Basel. This had impact primarily in Europe: it was not well marketed in North America. Several chapters continue to be cited, but I was disappointed in the outcome.
- Evolution in health and disease. 1998. Oxford University Press. This resulted from a conference I organized in 1996 that aimed to put Darwinian medicine on a more rigorous foundation. It has sold well and has been influential worldwide. The second edition, containing 95% new material, appeared in 2008.
- Evolution Illuminated: Salmon and their relatives. 2004. Oxford University Press. Andrew Hendry (McGill University) is senior editor. This book aims to show evolutionary biologists what salmon can teach them and salmon biologists what they can learn from evolution. It is too soon to assess its impact.
Important review articles:
- Stearns, S.C. 1976. Life history tactics: A review of the ideas. Quarterly Review of Biology 51: 3-47.
- Stearns, S.C. 1977. The evolution of life-history traits: A critique of the theory and a review of the data. Annual Review of Ecology and Systematics 8: 145-171.
- Stearns, S.C. 1989. The evolutionary significance of phenotypic plasticity. Bioscience 39: 436-445.
- Stearns, S.C. 1989. Tradeoffs in life-history evolution. Functional Ecology 3: 259-268.
- Stearns, S.C., G. de Jong, and R. Newman. 1991. The effects of phenotypic plasticity on genetic correlations. Trends in Ecology and Evolution 6: 122-126.
- Stearns, S.C. 1994. The evolutionary links between fixed and variable traits. Acta Paleontologica Polonica 38: 215-232.
- Stearns, S.C. 2000. Daniel Bernoulli (1738): evolution and economics under risk. Journal of Biosciences 25: 221-228.
- Stearns, S.C. 2002. Darwinian Medicine. Introductory Essay In M Pagel (ed.), Oxford Encyclopedia of Evolution, Oxford University Press.
- Sultan, S. & S.C. Stearns. 2005. Environmentally contingent variation. In Hallgrimsson, B. & B.K. Hall (eds), Variation: A Hierarchical Examination of a Central Concept in Biology. Academic Press pp. 303-332.
- Stearns, S.C., Allal, N. & Mace, R. 2007. Life history theory and human development. In Crawford, C. & Krebs, D. (eds)., Handbook of Evolutionary Psychology, pp. 47-69.
- Nesse, R.M. & Stearns, S.C. 2008. The great opportunity: Evolutionary applications to medicine and public health. Evolutionary Applications 1: 28-48.
- Stearns, S.C., Byars, S.G., Govindaraju, D.R., Ewbank, D. 2010. Measuring selection in contemporary human populations. Nature Reviews Genetics doi:10.1038/nrg2831.
Other contributions to the field:
While in Switzerland I helped to stimulate the development of evolutionary biology and graduate education in Europe through the following activities:
- I played the leading role in founding the European Society for Evolutionary Biology, which sponsors
- the Journal of Evolutionary Biology, where I was the founding editor (1986-1991). It has become one of the major journals in the field.
- I wrote the grant for, and ran, the European Science Foundation Program in Population Biology, which lasted 5 years and put on conferences and provided postdoctoral and faculty exchanges throughout Europe.
- With T.H. Clutton-Brock of the University of Cambridge, I founded the Tropical Biology Association, which puts on field courses in ecology, evolution, conservation, and behavior in Africa with students drawn 50% from Europe and 50% from African host countries. The TBA now has more than 500 graduates.
- My pedagogical innovations are described in Designs for Learning.
- My assistants and graduate students in Basel have gone on to distinguished careers, including these:
- Paul Schmid-Hempel, Professor, ETH Zurich, Switzerland
- Chistophe Boesch, Director, Max-Planck-Institut, Leipzig, Germany
- Fritz Vollrath, Professor and Chair, Zoology, Aarhus, Denmark
- Arie van Noordwijk, Professor, Avian Ecology, Utrecht, The Netherlands
- Bruno Baur, Associate Professor, Conservation Biology, Basel, Switzerland
- Jacob Koella, Professor of Epidemiology, Imperial College (Ascot)
- Dieter Ebert, Professor, Zoology, Basel, Switzerland
- Michael Doebeli, Associate Professor, Mathematics and Zoology, University of British Columbia
- Marta Manser, Professor, Zoology, University of Zurich, Switzerland
- Christine Mueller, SNF Research Professor, Environmental Science, University of Zurich, Switzerland
- Barbara Hellriegel, Senior Lecturer, Anthropology, University of Zurich, Switzerland
- Tad Kawecki, Associate Professor, Ecology and Evolution, Lausanne, Switzerland
- Giorgina Bernasconi, Associate Professor, Ecology and Evolution, Lausanne, Switzerland
- Martin Ackermann, SNF Research Professor, ETH Zurich
- Pascal Gagneux, Assistant Professor, UCSD Medical School
- Three my students at Reed College are now professors: Susan Alberts at Duke, Patrick Phillips at Oregon, and Rus Hoelzel at Durham.