plex, multicellular organisms. Why don't organisms instead choose asexual reproduction, which is a bit riskier (no built-in mechanism for preventing the accumulation of mutations) but typically quicker (no time spent in finding a suitable mate). In a new mathematical model that directly addresses the evolutionary advantage for sexual reproduction in complex organisms, Emmanuel Tannenbaum of Ben Gurion University (etannenb@gmail.com) considers a replicating population of single-celled organisms, whose genomes consist of two chromosomes, and applies some simplifying assumptions (e.g., any mutation in a chromosome renders it defective). If the cells replicate slowly, he finds, so that the time lost in finding a mate is small compared to the time it takes to replicate, then the benefit from recombination (i.e., the contribution of genetic material from two distinct organisms) is sufficiently large to make sexual replication the preferred strategy. This conclusion differs from previous notions, which assumed that sexual replication was simply more advantageous in all small populations, while the new analysis suggests for possibly the first time that sexual reproduction is advantageous only in those small populations with low replication rates. (W29.15)

SEARCHING FOR SUPERSOLIDS
In 2004 evidence for superfluid behavior in a solid, solid helium, was reported for the first time. Then at last year's APS March meeting Tony Clark and Moses Chan of Penn State said that they have obtained evidence also for superfluidity in solid hydrogen. Because the existence of a superfluid solid would require much new thinking about macroscopic quantum behavior, the number of theoretical papers on this topic have been increasing rapidly, and several groups have commenced experimental studies. At this year's meeting, Chan's group will be reporting more definitive results on these two supersolid systems. Other groups may hav
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Contact: James Riordon
riordon@aps.org
301-209-3238
American Physical Society
17-Mar-2006

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