torstaina, kesäkuuta 23, 2022

Karibian "väestönvaihdon" yksityiskohdat selviävät muinaisen DNA:n tutkimuksen kautta

Intiaaniväestö Karibian saarilla on tunnetusti hävinnyt lähes kokonaan. 

Historian aikana on kiistelty siitä, kuinka paljon asukkaita saarilla oli ennen valkoisten tuloa. Arviot ovat vaihdelleet miljoonasta (Christopher Columbus ja hänen veljensä Bartholomewn arviot) melkein nollaan (John Locke). Nykyarvio oli vuoteen 2020 saakka noin 250 000. Muinaisen DNA:n tutkimus on nyt antanut uutta valoa kysymykseen (David Reich ja kumppanit vuonna 2020). Intiaaneja lienee ollut vain muutamia kymmeniä tuhansia.

The finding about the pre-contact population size in Hispaniola was made possible by a new scientific advance: We are now able to detect “DNA cousins” in ancient genomes — taking two people and determining whether they share large segments of DNA inherited from a recent ancestor. This is similar to what personal ancestry companies like 23andMe and Ancestry do with living people.

When the Reich team applied this method to 91 ancient individuals for whom it had sequenced enough of the genome to carry out this analysis, it found 19 pairs of DNA cousins living on different large islands or island groups in the Caribbean: for example, an individual in Hispaniola with a cousin in the Bahamas, and another individual in Hispaniola with a cousin in Puerto Rico. This meant that the entire population had to be very small; you wouldn’t find that random pairs of people had such a high probability of being closely related if the entire population was large. (To put this in perspective, if you did the same analysis on random pairs of people across China today, DNA cousins would be detected many thousands of times less often.)

The rate of close relationships that the Reich team found is what would be expected for about 3,000 people — at most 8,000 people — in their childbearing years in Hispaniola. The true numbers of people could have been threefold to tenfold larger because at any given time only a fraction of a population is in its childbearing years. Still, we can confidently conclude that the pre-contact population size of Hispaniola was no more than a few tens of thousands of people.

Intiaanit hävisivät itse asiassa vain muutamissa kymmenissä vuosissa valkoisten saapumisesta. Toisaalta muinaisen DNA:n tutkimus osoittaa, että itse asiassa he eivät hävinneet kokonaan vaan osittain sulautuivat mm. afrikkalaisperäisiin orjiin.

Lisäksi Karibian alkuperäisväestö ennen Kolmubusta ei ollut kovinkaan alkuperäistä, vaan 1000 vuotta ennen Kolumbusta väestö oli ilmeisesti jo kerran vaihtunut samalla tavalla

Tutkimus on antanut myös mielenkiintoista tietoa Karibian intiaanien elämäntavasta:

In addition, by illuminating the highly mobile lifestyle of pre-contact Caribbean people with many DNA cousins across different islands, the research underscores the degree to which they were connected.

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