My daughter Julia came up with a brilliant idea: partial birthdays by relatedness. It goes like this. Say your birthday is on 1 January. On that day, you have a birthday. Imagine your daughter’s birthday is 1 June. On that day, you have a half-birthday, because your daughter shares half of your genes, because she got from you half of your genes. The implications of this idea of partial birthdays are staggering.
What this means is that today, my daughter’s birthday, I have a half birthday, and as a result, I think I will go out and celebrate. I don’t know if anyone is going to give me half-presents, but I can certainly hope.
But it gets better. Each of my first cousins has 12.5% of my genes by direct descent. Thus, on one of my first cousin’s birthday’s, I have a 0.125 birthday. One could carry this on to an extreme, and note that as every human shares at least a bit of my DNA by descent, that means every day of the year is a partial birthday for me! And for you!
And, at least for me, it gets even better, as I have an identical twin. That means that on my birthday, I have a 2.0 birthday! A double birthday! (Actually, it would be more than a 2.0 birthday, as there would be all those other people in the world with the same birthday to whom I am at least a little bit related.) And, it means I get 0.5 birthdays on the birthdays of each of his children! I can see many celebrations in the year ahead…