Genes and Genealogies: Reflections on our Biological and Social Inheritance

by Irene Velasco

Have you ever heard that Charles Darwin, George Washington, Jane Austen, Humphrey Bogart or Lord Byron were descendants of Edward III? Even more, what if we were told that 80% of British people nowadays are descendants of Edward III? Probably, we will think that someone is pulling our leg. However, that was the beginning of the speech by Susanna Manrubia in the weekly Small Talk session at the EOI in Valdemoro.

Susanna Manrubia is a physicist who works at the Spanish National Biotechnology Center (CSIC). She researches about Evolutionary Systems, the relationship between genotype and phenotype, molecular and viral evolution and she is also interested in cultural patterns and collective social behaviour. What an interesting person!

She patiently and splendidly explained to us the way our ancestors converge at some point in the past due to what she called the “Grandparents Paradox”. To illustrate this, she used the royal genealogical tree of Edward III, where some ancestors appear up to six times, since nobles usually married within their own families. In Spain, we also have another example of this: Felipe II, whose both grandmothers were daughters of The Catholics Kings. Similarly, in a large scale, the tree of an individual joins other genealogical trees because their relatives appear repeatedly in the tree. The more we look into the past, the more repeated individuals we will find. Thus, we share ancestors. Furthermore, we have exactly the same ancestors at some point in the past.

The moral of this story is if we choose two random individuals and we go back into their past generations, they have got the same group of ancestors and it appears equal number of times in both of them.

On the grounds that we all come from the same ancestor, the question that comes to our mind is: Why are we so different to each other? Where is our diversity? Much to our surprise, the answer is simple: genealogy is not the same as genetics. Susanna showed us through different pictures how we receive 50% of our genes randomly from each of our parents and, as we go generations back, these genes are diluted into uncountable ancestors. For instance, at eight generations back, none of our genes comes from any given ancestor. We can have a well-known ancestor as Edward III or Genghis Kahn, but we have not inherited anything from their genome. Rather, each of our genomes is unique and make us special.

In the light of the above, on the philosophical question “Who are we?”, we can say that not only are genes and genealogy involved, but there are also a lot of other cultural, social and historical factors to take into account to answer this question accurately. Sussana Manrubia certainly gave us some food for thought!

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