Saturday, 11 February 2017

Longevity and Migration

There has been a flood of articles from the academic community in the past few days using genealogical and genetic genealogical big data. They are aimed at the academic community, replete with technological terminology so that I doubt one in a hundred genealogists can critically evaluated the articles' methodology and results. I count myself in the 99%.

Quantitative analysis of population-scale family trees using millions of relatives, available as a preprint, not yet peer reviewed, is one the layman stands a bit more of a chance of understanding.

The study draws on data for 86 million individuals contributed by more than 3 million genealogists to geni.com, a division of MyHeritage. Quality control to eliminate obvious errors yielded a database of 5.3 million separate family trees the largest of which contained 13 million individuals and spanned 11 generations. About 30% came from North America, 50% from Western Europe and Scandinavia, 5% from the British Isles, and the remainder more than 100 other countries.

Testing these trees against a small DNA database showed a non-paternity rate of 1.9% and non-maternity rate of 0.3% per generation (meiosis).

The heat map has colours corresponding to the fraction of deaths reported at a certain age per year. Notice the decrease in infant and child mortality since the 19th century.

Regarding longevity the study found a tendency for longer-lived parents to have longer-lived children but less so than in previous studies. There was a slightly increased tendency for men to live longer if their father did and the same for women and their mother. However, hereditary was much less of a factor than environment overall.

On migration it was found that females migrated more but over shorter distances than males in Western societies. That’s consistent with women moving to the husband’s workplace on marriage. Men showed a greater tendency for longer range migration as shown by his children being born in a different country than the father, but not so much for the mother.

Couples born in adjacent locations are more likely to be genetically related - 4th cousins before 1850. Later society became more mobile and couples were more likely to be born further apart (greater marital distance). For every 70Km increase in marital distance the genetic distance relationship increased by one meiosis.

There's much more in the article, which also includes information on how to access the anonymised database, at www.biorxiv.org/content/early/2017/02/07/106427.1

As I was writing this item the news arrived that Yaniv Erlich, corresponding author of the study, has been appointed Chief Scientist at MyHeritage.

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