In addition to the corrections already made, I offer a few more corrections (in red), and a stylistic suggestion (in blue):

According to some scientists the total number of people who have ever lived on Earth is estimated to number around 106 billion. 

They calculated the number of all modern humans (homo sapiens) who have lived . . .  . the first modern humans evolved much earlier, perhaps 100 thousand years ago in Southeast Africa.
So that makes the current population of earth of around 7 billion, only 6 or 7 percent of the total number of human beings who have ever lived, which is not what I thought previously (that more people are alive at present than had ever lived previously in the whole of human existance)

some musings

Some time ago while I was surfing the Internet I came across an interesting article.
According to some scientists, the whole number of people who ever lived on Earth is estimated at around 106 billion .
They calculated the number of all modern humans (homo sapiens) who lived in the last 50 thousand years, though I think that the first modern humans evolved much earlier, maybe 100 k years ago in Southeast Africa.
So that makes the current population of Earth of around 7 billion only 6 or 7 per cent of the whole number of human beings, which is not as I thought previously.
(that more people are alive at present than ever lived in the whole of human existance)