Page 228 - People & Places In Time

Addendum
in 1492, “you begin to see the European genes flowing in every direction until our estimates are that there are no people in South America today who don’t have European ancestry.”
In fact, even more recent than the global genetic isopoint is the one for people with recent European ancestry. Researchers using genomic data place the latter date around A.D. 1000. So, Christopher Lee’s royal lineage is unexceptional: because Charlemagne lived before the isopoint and has living de- scendants, everyone with European ancestry is directly descended from him. In a similar vein, nearly everyone with Jewish ancestry, whether Ashkenazic or Sephardic, has ancestors who were expelled from Spain beginning in 1492. “It’s a very nice example of a small world but looking to the past,” says Susanna Manrubia, a theoretical evolutionary biologist at the Spanish National Center for Biotechnology.
Not everyone of European ancestry carries genes passed down by Charlemagne, however. Nor does every Jew carry genes from their Sephardic ancestors expelled from Spain. People are more closely related genealogically than genetically for a simple mathematical reason: a given gene is passed down to a child by only one parent, not both. In a simple statistical model, Manrubia and her colleagues showed that the average number of generations separat- ing two random present-day individuals from a common genealogical ancestor depends on the logarithm of the relevant population’s size. For large popula- tions, this number is much smaller than the population size itself because the number of possible genealogical connections between individuals doubles with each preceding generation. By contrast, the average number of generations separating two random present-day individuals from a common genetic ancestor is linearly proportional to the population size because each gene can be traced through only one line of a person’s family tree. Although Manrubia’s model unrealistically assumed the population size did not change with time, the results still apply in the real world, she says. Because of the random reshuffling of genes in each successive generation, some of your ancestors contribute disproportionately to your genome, while others contribute nothing at all. According to calculations by geneticist Graham Coop of the University of California, Davis, you carry genes from fewer than half of your forebears from 11 genera- tions back. Still, all the genes present in today’s human population can be traced to the people alive at the genetic isopoint. “If you are interested in what your ancestors have contributed to the present time, you have to look at the population of all the people that coexist with you,” Manrubia says. “All of them carry the genes of your ancestors because we share the [same] ancestors.”
And because the genetic isopoint occurred so recently, Rutherford says, “in relation to race, it absolutely, categorically demolishes the idea of lineage purity.” No person has forebears from just one ethnic background or region of the world. And your genealogical connections to the entire globe mean that not too long ago your ancestors were involved in every event in world history.
So, the next time you hear someone claim to be descended from royalty, take heart: you are, too. “You are very special, and you are very generic, in a sense,” Manrubia says.
P ~ Firemens little league team ~ Exeter Sun about 1957-58
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