This post has red flags running through it. Maybe a typo by you Steve but world population around 1600 was over 500 million people. And whilst population continues to grow world population is projected to begin a decline later this century after we reach 10 billion in about 60 years. Male fertility is falling and with cost of living, particularly in the west, people are more often choosing not to have children or limit the family size to a small number.
I hope I will be stood corrected as you have pointed out but given the deterioration of the planets eco system estimates of what our planet - Mother Earth - can tolerate may be much more dismal.
A summary from Google supports my views;
