On November 1, across Latin America but especially in Mexico, the cemeteries come alive—with a celebration.

It’s Dia de los Muertos, the Day of the Dead. Legend has it the gates of heaven open for a day to allow the souls of the dead to reunite with loved ones.

It’s considered disrespectful to mourn the dead, so families bring food and drink, clean and decorate gravestones, sing, and dance, fly brightly colored kites, and tell stories about and for the deceased.

Dia de los Muertos is a melding of the Catholic All Saints’ Day brought by the Spanish with the centuries-old tradition of ancestor worship by the native peoples.

Just how many ancestors could we be celebrating? Some enterprising statisticians decided to figure that out.

This took a lot of ciphering and, for different places and eras, assumption—about infant mortality, birthing age of women, size of families, survival rates of disease, the impacts of drought, famine, and war on populations.

In the end, they calculated that 109 billion deceased people have preceded the 8 billion alive today, for a very grand total of 114 billion humans who have occupied Earth.

In 2050, when population is projected to peak around 10 billion, there will be some 110 billion ancestors to worship.

Now that will be a Dia de los Muertos to remember!