Although confined to western European populations, this article seems to provide empirical evidence to validate several earlier papers on the theoretical relatedness of humans throughout the world.

Ralph P, Coop G (2013)

The Geography of Recent Genetic Ancestry across Europe.

PLoS Biol 11(5): e1001555. doi:10.1371/journal.pbio.1001555

http://www.plosbiology.org/article/info%3Adoi%2F10.1371%2Fjournal.pbio.1001555#abstract1

Abstract

The recent genealogical history of human populations is a complex mosaic
formed by individual migration, large-scale population movements, and other
demographic events. Population genomics datasets can provide a window into
this recent history, as rare traces of recent shared genetic ancestry are
detectable due to long segments of shared genomic material. We make use of
genomic data for 2,257 Europeans (in the Population Reference Sample
[POPRES] dataset) to conduct one of the first surveys of recent
genealogical ancestry over the past 3,000 years at a continental scale.

We detected 1.9 million shared long genomic segments, and used the lengths of
these to infer the distribution of shared ancestors across time and
geography. We find that a pair of modern Europeans living in neighboring
populations share around 2–12 genetic common ancestors from the last 1,500
years, and upwards of 100 genetic ancestors from the previous 1,000 years.
These numbers drop off exponentially with geographic distance, but since
these genetic ancestors are a tiny fraction of common genealogical
ancestors, individuals from opposite ends of Europe are still expected to
share millions of common genealogical ancestors over the last 1,000 years.

There is also substantial regional variation in the number of shared
genetic ancestors. For example, there are especially high numbers of common
ancestors shared between many eastern populations that date roughly to the
migration period (which includes the Slavic and Hunnic expansions into that
region). Some of the lowest levels of common ancestry are seen in the
Italian and Iberian peninsulas, which may indicate different effects of
historical population expansions in these areas and/or more stably
structured populations. Population genomic datasets have considerable power
to uncover recent demographic history, and will allow a much fuller picture
of the close genealogical kinship of individuals across the world.