how do dna testing companies calculate the percentages of your origin and how can they be so exact?
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DNA testing is for fun and a few interesting conversations. In the scheme of things it means nothing because lines drawn on a map (that change with every war/conquest) are not respected by genetic transmission.
DNA testing companies do not have a “pure sample” of any “origin”. All they have are a sample from the population TODAY. Trying to work backwards to some inference is purely a mathematical game at that point – fraught with assumptions, best guesses and correlations. None, zero, naught, nil of these methods are deterministic. The best they get is that “a lot of people who call themselves A have some of this and some of that and maybe we’ll call this a marker for A”. Then as more and more samples are collected, the weaker and weaker these correlations become.
It is a guessing game based on statistics, nothing more. And one thing that everyone needs to understand with statistics – it is IMPOSSIBLE to derive a particular individual characteristic from a population statistic. The simplest example is to flip a coin for heads and tails – in the long term there is a 50/50 statistical outcome but there are ZERO coins with a side of 50/50 heads-tails, a side with either be 100% heads or 100% tails.
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