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Genetic and paleoanthropological evidence is in accord that today's human population is the result of a great demic (demographic and geographic) expansion that began approximately 45,000 to 60,000 y ago in Africa and rapidly resulted in human occupation of almost all of the Earth's habitable regions. Genomic data from contemporary humans suggest that this expansion was accompanied by a continuous loss of genetic diversity, a result of what is called the "serial founder effect." In addition to genomic data, the serial founder effect model is now supported by the genetics of human parasites, morphology, and linguistics. This particular population history gave rise to the two defining features of genetic variation in humans: genomes from the substructured populations of Africa retain an exceptional number of unique variants, and there is a dramatic reduction in genetic diversity within populations living outside of Africa. These two patterns are relevant for medical genetic studies mapping genotypes to phenotypes and for inferring the power of natural selection in human history. It should be appreciated that the initial expansion and subsequent serial founder effect were determined by demographic and sociocultural factors associated with hunter-gatherer populations. How do we reconcile this major demic expansion with the population stability that followed for thousands years until the inventions of agriculture? We review advances in understanding the genetic diversity within Africa and the great human expansion out of Africa and offer hypotheses that can help to establish a more synthetic view of modern human evolution. [ABSTRACT FROM AUTHOR]

The island of Crete, credited by some historical scholars as a central crucible of western civilization, has been under continuous archeological investigation since the second half of the nineteenth century. In the present work, the geographic stratification of the contemporary Cretan Y-chromosome gene pool was assessed by high-resolution haplotyping to investigate the potential imprints of past colonization episodes and the population substructure. In addition to analyzing the possible geographic origins of Y-chromosome lineages in relatively accessible areas of the island, this study includes samples from the isolated interior of the Lasithi Plateau – a mountain plain located in eastern Crete. The potential significance of the results from the latter region is underscored by the possibility that this region was used as a Minoan refugium. Comparisons of Y-haplogroup frequencies among three Cretan populations as well as with published data from additional Mediterranean locations revealed significant differences in the frequency distributions of Y-chromosome haplogroups within the island. The most outstanding differences were observed in haplogroups J2 and R1, with the predominance of haplogroup R lineages in the Lasithi Plateau and of haplogroup J lineages in the more accessible regions of the island. Y-STR-based analyses demonstrated the close affinity that R1a1 chromosomes from the Lasithi Plateau shared with those from the Balkans, but not with those from lowland eastern Crete. In contrast, Cretan R1b microsatellite-defined haplotypes displayed more resemblance to those from Northeast Italy than to those from Turkey and the Balkans.European Journal of Human Genetics (2007) 15, 485–493. doi:10.1038/sj.ejhg.5201769; published online 31 January 2007 [ABSTRACT FROM AUTHOR]

Mitochondrial DNA and the Y chromosome have been used extensively in the study of modern human origins and other phylogenetic questions, but not in the context of their sex-specific modes of transmission, mtDNA is transmitted exclusively by females, whereas the Y chromosome is passed only among males. As a result, differences in the reproductive output or migration rate of males and females will influence the geographic patterns and relative level of genetic diversity on the Y chromosome, autosomes and mtDNA (ref. 1). We have found that Y chromosome variants tend to be more localized geographically than those of mtDNA and the autosomes. The fraction of variation within human populations for Y chromosome single nucleotide polymorphisms (SNPs) is 35.5%, versus 80-85% for the autosomes and mtDNA (refs 6-8). A higher female than male migration rate (via patrilocality, the tendency for a wife to move into her husband's natal household) explains most of this discrepancy, because diverse Y chromosomes would enter a population at a lower rate than mtDNA or the autosomes. Polygyny may also contribute, but the reduction of variation within populations that we measure for the Y chromosome, relative to the autosomes and mitochondrial DNA, is of such magnitude that differences in the effective population sizes of the sexes alone are insufficient to produce the observation. [ABSTRACT FROM AUTHOR]