Looking for Clues: Cassandra Extavour, a developmental biologist at Harvard searches for genetic clues to the origin of multicellularity and the complex organisms that multicellularity made possible, including Homo sapiens. Image: David Behl
Developmental biologist Cassandra Extavour sings classical and baroque music on stage with the Handel and Haydn Society at Symphony Hall in Boston. Blessed with a beautiful soprano voice, she could easily have chosen to pursue a career as a singer. But a summer working in a developmental genetics laboratory as an undergraduate tipped the scales in favor of science, and Extavour is now an associate professor of organismic and evolutionary biology at Harvard University. By choosing biology, she says, she has been able to pursue her musical career part time; a full-time concert soprano, by contrast, would not have had the time to run a lab on the side.
Extavour directs a national research collaborative called EDEN, which stands for Evo-Devo-Eco (evolutionary-developmental-ecological) Network. The organization, funded by the National Science Foundation, encourages geneticists to dissect more exotic creatures than the ubiquitous fruit fly, Drosophila melanogaster. EDEN researchers model the various evolutionary paths of sea anemones, horseshoe crabs, mosses, crickets, spiders, milkweed bugs and the super-hardy tardigrade. Extavour’s own lab focuses on dissecting insect embryos and ovaries, searching for genetic clues to the origin of multicellularity and the complex organisms that multicellularity made possible, including Homo sapiens. Extavour's special expertise is in tracking the development of germ cells, the cells created in an embryo that contain the genetic code for reproducing multicellular organisms.
Last winter, Extavour was one of the organizers of a ten-week program on a controversial topic, "Cooperation and the Evolution of Multicellularity," at the Kavli Institute for Theoretical Physics at the University of California, Santa Barbara. The daily talk sessions were attended by scores of highly regarded scientists from all over the world, including developmental and evolutionary biologists, mathematical physicists, and zoologists—plus an embedded journalist reporting for Quanta Magazine. The event was unusual because of its prolonged and multidisciplinary nature. And many exchanges were heated because, despite 150 years of research on the biology of evolution, scientists still disagree about how and why multicellular creatures and plants emerged from ancient oceans that teemed with robust and self-reliant single-celled entities.
At the conference, biologists who work mostly in the field observing the behaviors of bees, ants, wolves, slime molds and other creatures tended to look for the mechanics of natural selection at the behavioral level by examining how individual organisms self-organize into hives, nests, packs, conglomerates or families. Physicists and molecular biologists focused more on the micromechanics of natural selection at the level of the genome, looking to mathematically measure the "fitness" of what they call competing and cooperating genes or cells.