According to the Population Reference Bureau, about 107 billion people have lived on Earth.

(They calculated it using stats and guesses from when Homo sapiens first walked the earth, about 50,000 years ago, and assumed that 50,000 years ago there was a population of 2.  I bet there was a humdinger of an argument about that statistic.)

How many people have ever lived?

Year Population Births / 1,000 Births since previous date
Source: Population Reference Bureau estimates
50,000BC 2
8,000BC 5,000,000 80 1,137,789,769
AD1 300,000,000 80 46,025,332,354
1200 450,000,000 60 26,591,343,000
1650 500,000,000 60 12,782,002,453
1750 795,000,000 50 3,171,931,513
1850 1,265,000,000 40 4,046,240,009
1900 1,656,000,000 40 2,900,237,856
1950 2,516,000,000 31-38 3,390,198,215
1995 5,760,000,000 31 5,427,305,000
2011 6,215,000,000 23 2,130,327,622
Number who have ever lived: 107,602,707,791