A pre-Columbian Y chromosome-specific transition and its implications for human evolutionary history.

A polymorphic C-->T transition located on the human Y chromosome was found by the systematic comparative sequencing of Y-specific sequence-tagged sites by denaturing high-performance liquid chromatography. The results of genotyping representative global indigenous populations indicate that the locus is polymorphic exclusively within the Western Hemisphere. The pre-Columbian T allele occurs at > 90% frequency within the native South and Central American populations examined, while its occurrence in North America is approximately 50%. Concomitant genotyping at the polymorphic tetranucleotide microsatellite DYS19 locus revealed that the C-->T mutation displayed significant linkage disequilibrium with the 186-bp allele. The data suggest a single origin of linguistically diverse native Americans with subsequent haplotype differentiation within radiating indigenous populations as well as post-Columbian European and African gene flow. The mutation may have originated either in North America at a very early time during the expansion or before it, in the ancestral population(s) from which all Americans may have originated. The analysis of linkage of the DYS199 and the DYS19 tetranucleotide loci suggests that the C-->T mutation may have occurred around 30,000 years ago. We estimate the nucleotide diversity over 4.2 kb of the nonrecombining portion of the Y chromosome to be 0.00014. compared to autosomes, the majority of variation is due to the smaller effective population size of the Y chromosome rather than selective sweeps. There begins to emerge a pattern of pronounced geographical localization of Y-specific nucleotide substitution polymorphisms.

Ancient Maya documents concerning the movements of Mars

A large part of the pre-Columbian Maya book known as the Dresden Codex is concerned with an exploration of commensurate relationships among celestial cycles and their relationship to other, nonastronomical cycles of cultural interest. As has long been known, pages 43b–45b of the Codex are concerned with the synodic cycle of Mars. New work reported here with another part of the Codex, a complex table on pages 69–74, reveals a concern on the part of the ancient Maya astronomers with the sidereal motion of Mars as well as with its synodic cycle. Two kinds of empiric sidereal intervals of Mars were used, a long one (702 days) that included a retrograde loop and a short one that did not. The use of these intervals, which is indicated by the documents in the Dresden Codex, permitted the tracking of Mars across the zodiac and the relating of its movements to the terrestrial seasons and to the 260-day sacred calendar. While Kepler solved the sidereal problem of Mars by proposing an elliptical heliocentric orbit, anonymous but equally ingenious Maya astronomers discovered a pair of time cycles that not only accurately described the planet's motion, but also related it to other cosmic and terrestrial concerns.