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Genetic age (TMRCA) of the main English Plant family

Documentary evidence suggests that the main English Plant family might have originated sometime around the early 14th century - that is, around 23 generations ago (assuming 30 years per generation). This agrees well with calculations based on the DNA results for the main cluster of matching Plants.

Jobling, Hurles and Tyler-Smith, Human Evolutionary Genetics, p 180, outline three methods for calculating the TMRCA (Time to the Most Recent Common Ancestor) for a cluster of near-matching Y-DNA signatures. These are called the variance method, the ASD method and the rho method. The following are the corresponding results, in number of generations, for the 67-marker and 37-marker clusters of near-matching Plant DNA signatures. [The calculations were made on the available DNA results at October 2012. The variance calculations are by Stephen Parrish, the ASD calculations by me, and the rho calculations by Prof Richard Plant.]

:variance : ASD :rho
67-marker : :22.5: 19.0 (SD=4.5)
37-marker :23.3 (coal=18.7):23.1:21.7 (SD=6.0)

As each person being DNA tested was not aged zero, it is appropriate to add one or more generations to these values. The SD (standard deviation) values are a measure of the number of generations of statistical uncertainty in the results. The "coal" (coalescence) value is an indication of the number of generations ago when the Plant family population "took off" as opposed to first coming into existence (TMRCA). For the TMRCA itself, there is the added complication that these calculations do not account for unusual events, such as the mid-14th century Black Death, and there is hence some additional uncertainty about whether the main Plant family population might have been progressing erratically earlier, perhaps back in the 13th century.

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