Melinda asks:

>Is it known how unrelated humans can be to each other? What could be
>the genomic difference (in percents?) between the least related
>humans? And as reference, how closely related are closely related
>humans (such as family members or larger groups)?

Anatomically modern humans, the only kind in existence now, are proving to be
more genetically monomorphic than anyone initially expected. The numbers that
are bandied about nowadays are that if you selected any two humans on the
planet, they would identical for about 99.9% of their genomes. 

Perhaps more impressive, of that less than 1% variation that exists in humans,
approx. 95% of the variation is found within all populations, not between
populations.

The most comprehensive study to date on human genetic variation was released
just a few weeks ago in Science. For more information, please see:

Genetic Structure of Human Populations. Noah A. Rosenberg, Jonathan K.
Pritchard, James L. Weber, Howard M. Cann, Kenneth K. Kidd, Lev A. Zhivotovsky,
and Marcus W. Feldman. Science Dec 20 2002: 2381-2385.

In that article, the authors write in their abstract: "We studied human
population structure using genotypes at 377 autosomal microsatellite loci in
1056 individuals from 52 populations. Within-population differences among
individuals account for 93 to 95% of genetic variation; differences among major
groups constitute only 3 to 5%. Nevertheless, without using prior information
about the origins of individuals, we identified six main genetic clusters, five
of which correspond to major geographic regions, and subclusters that often
correspond to individual populations. General agreement of genetic and
predefined populations suggests that self-reported ancestry can facilitate
assessments of epidemiological risks but does not obviate the need to use
genetic information in genetic association studies."

What becomes confusing are how the percentages are calculated, thus let me say
again, any two humans will generally prove to be 99.9% identical for their
genomes, but of that variation that does exist, 95% of that variation exists
within all human populations. Only 3 to 5% of that variation is specific to any
one group.

Wirt Atmar
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