|A religious-view visual, from the article “What are the Demographics of Heaven?” (2015) (Ѻ), of god creating humans (aka nature synthesizing humans), based on the “god creating Adam” (c.1512) painting by Michelangelo, which itself is based, religio-mythological speaking, on the 3100BC Heliopolis creation myth of the god Atum being self-engendered out of the watery god Nun, of the notion of the number of people who have existed.|
In 1981, Carl Haub, a demographer at the Population Reference Bureau, got a call from someone saying that they had heard that "75% of the people ever born, in human history, were living in that year", after which, puzzled by this statement, which he intuited was a off estimate, he began researching the topic of the number of people who have ever existed. 
In 1995, Haub, in his “How Many People Have Ever Lived on Earth”, calculated that 105 billion people “have lived on earth, of whom 5.5% are alive today”. 
In 2005, Libb Thims, independent of Haub, in his Cessation Thermodynamics manuscript, calculated that about 81 billion people have come into existence.
1. Haub, Carl. (2011). “Distilled Demographics: How Many People Have Ever Lived on Earth?” (vid), YouTube, Population Reference Bureau, Oct 3.
2. Haub, Carl. (1995). “How Many People Have Ever Lived on Earth” (abs), Population Today, 23(2):4-5, Feb.