You might think that birthdays would be distributed along the calendar fairly randomly, but we know human beings don't operate in a random way. There are more babies born on September 9th than any other day of the year. The next most common birthdays are September 19th and September 12th. The rest of the top ten birthdays are also in September, between the 9th and the 20th. February 29th is the least common birth date, for obvious reasons.
Why are these the most common dates? Count back 38 weeks to the conception date for these folks, and it seems obvious: holidays, parties, alcohol, and it's nice to snuggle close to your partner on a cold night. But there may be other reasons, according to scientists, having to do with the changing seasons and temperatures affecting fertility. Mental Floss goes over those for us.
We also know that more babies in the US are born on Tuesday than any other day of the week. This is also not random. Doctors like to golf on Wednesdays.
(Image credit: James Petts)