In my family there are several pairs of people who share birthdays. If you consider my paternal grandmother and her ten descendants, seven share a birthday with another and three more are within a couple of days of another. Perhaps this image will help:
M=male; F=female. spouses are left out of the diagram. My grandmother is at the top and I’m at the lower left. The two sisters with the same birthdate are twins; otherwise there is a 5, 29, or 67-year interlude between the matched birthdays. To my knowledge, none was born caesarean or via induced labor.
So: Is there any explanation for this other than coincidence? Can some sort of psychosomatic effect make conception or labor likelier on one date over another? I have heard of some really extreme cases of this phenomenon (six or eight or ten people with the same b’day over multiple generations), but nobody I know personally has anything like it in their family. Does anyone on the board have this sort of thing going on with their relatives?
Well, first of all, it’s surprising how often shared birthdays occur in a group of people. For example, in a group of 23 people, the probability that at least two of them share a birthday is a little better than 1/2–a lot higher than most would guess.
Next, you have to realize that that is under the assumption that birthdays occur randomly, which I don’t think is entirely true. That means that the probability of shared birthdays is even (slightly) higher than random chance would indicate (which, as I already mentioned, is already high). (This, by the way, is sometimes known in math/probability as the Birthday Inequality).
So, no, I don’t think it’s all that rare, and, in fact, I don’t think it’s all that surprising, mathematically, either.
Today is my birthday, as well as my best friend’s.She and I are 15 minutes apart.
My brother and his best friend share the same b’day, one year apart.
That doesn’t really help answer your question, but I just thought it was an interesting coincidence that you should start this thread today
Could it possibly have something to do with better times for conception?Kinda like how so many babies seem to be born in spring/early summer after a particularly cold winter?What else are you supposed to do to get warm?
Birth rates in the US aren’t even throughout the year. The highest rates are in August and September (think winter) and the lowest ones are in March and April I believe (think summer). However, I don’t the differences would be great enough to explain such a small group that the OP referred to.
I have very often been in a group of people when this subject comes up. Most of the time there ARE two people with the same birthday. However, I have NEVER met someone who’s birthday is 16 February. Anyone want to make me feel less lonely?
My two step-sisters and my father all share the same birthday (in different years).
Also, my birthday and my sister’s birthday are one day (+ 3yrs) apart.
A drag to share your birthday party as a kid. But I always took solace because my step-brothers birthday was the day after Christmas. My religous grandmother would make a cake that said happy birthday to Jesus and Adam. And you can guess who got top billing.
With over 20 million families in the US alone, surely someone has to have a family birthday tree such as yours. The probability is near certanty. The only coincidence (to you) is it’s YOUR family and not someone elses. Life is full of coincidences. Live with them.
