Searching for an alien haven in the heavens

Abstract

Searching for an alien haven in the heavens T he first few articles in this issue of PNAS constitute the beginning of a two-part Special Feature dedicated to the study of astrobiology. Astrobiology is not an autonomous or self-sustaining discipline. Rather, it is a hybrid subject emerging at the crossroads of astronomy, geology, paleontology, physics, and biology. What at first pass may seem like an amalgamation of disparate fields, upon further review, is a clear and increasingly defined discipline. The roots of astrobiology are found in the 10 distinct goals set by the National Aeronautics and Space Administration (NASA) Astrobiology Institute. These objectives can be summarized into three branches: How does life begin and develop? Does life exist elsewhere in the universe? What is life's future on Earth and beyond? Some preliminary answers to these questions were addressed at the first large scientific conference dedicated entirely to astrobiology, held April 25-26, 2000 at the Ames Research Center at Moffett Field, CA. A few months later an international ''Frontiers of Life'' conference was held in France's Loire Valley. Sessions at those meetings ranged from ''Water-the Sine Qua Non of Life,'' which covered the water reservoirs on Jupiter's moon Europa; ''Environment,'' which covered snowball earth, life in extreme environments, the evolution of biochemisty, and interstellar quinones; ''Life Detection Methods and Biosignatures''; and ''Detection Methods for Extrasolar Planets.'' Many of these topics are expounded in this issue of PNAS, and it is clear that the two premier conferences marked the official beginning of a wave of discourse that undoubtedly has as many opinions as voices. Early astrobiology had some high-profile skeptics like French biologist Jacques Monod who in 1971 categorically dismissed the field. He reasoned that the ''unfeeling immensity of the Universe'' left one to conclude that biological organization emerged alone and by chance in a phenomenal chemical fluke (1). In 1964 American

High Levels of Genetic Differentiation between Ugandan Glossina fuscipes fuscipes Populations Separated by Lake Kyoga

“…Significant negative departures of these tests are caused by an excess of new mutations resulting from evolutionary forces such as selective sweeps or population expansion. Processes that maintain an excess of old mutations result in positive departures [55] . The mtDNA sequence data have been submitted to Genbank under accession nos EU559605-EU559621 (COII) and EU562262-EU562281 (CytB).…”

Genetic Variation among Major Human Geographic Groups Supports a Peculiar Evolutionary Trend in PAX9

“…In about 60,000 years, modern humans left Africa and colonized all other continents, with the exception of Antarctica [35] , [36] . Since then, human populations have lived in an extraordinary variety of habitats.…”

“…However, since it is well-known that these parameters are also affected by the demographic histories of the population considered [29] , we incorporated in the analysis coalescence simulations using Rogers' algorithm [46] as implemented by [47] in the DFSC 1.1 software ( www.xmission.com/~wooding/DFSC/ ). Distinct scenarios on times of expansion and initial population sizes compatible with the available data were simulated as follows: 1) For all samples, initial populations of 1,000 or 10,000 individuals [48] , [49] starting 60,000 years ago [35] , [36] , [49] ; 2) For all non-African populations, initial population of 10,000, date 40,000 years ago; 3) For Japanese only, 3,000 starting individuals, date 37,000 years ago [50] ; 4) For the Native American and Eskimo dataset, initial populations of 80 or 500 individuals [51] , [52] , starting 18,000 years ago [51] , [53] . For all scenarios described above we considered assumptions of population growth ranging from 1-fold (stationary) to 100-fold.…”