Multicellular life from a test tube
In less than two months, yeast in a test tube evolved from single-celled life to bristly multicellular structures. The new, snowflakelike forms act like multicellular organisms, reproducing by splitting when they reach large sizes and evolving further in response to harsh conditions, William Ratcliff of the University of Minnesota, Twin Cities reported in Norman, Okla., at the Evolution 2011 meeting (SN: 7/16/11, p. 11).
To create pressure to evolve in the experiment, Ratcliff and his colleagues subjected tubes of yeast in liquid to a daily ordeal: a mild spin in a centrifuge and then removal of all but the sludge with the heaviest yeast. Yeasts reproduce by budding, and cells that continued clinging to their daughter buds after cell division probably landed in the sludge and survived. Under pressure from these daily tosses, yeast lineages started holding onto bud