The United Nations estimates that on October 31st, the world’s population will reach 7 billion.  Although the actual number is not certain, it does underlie the fact that our population is growing at an alarming rate.  It took until the early 1800’s to reach the 1 billion mark, but the last 50 years alone have seen the births of 4 of the total 7 billion  This rapid increase raises the question, how many more people can the earth sustain?  Or have we already surpassed the earth’s capacity?  Among the many people asking questions like this are Dr. Madeline Weld, President of the Ottawa-based Population Institute of Canada, and Robert Engelman, President of The Worldwatch Institute in Washington.  They discuss how various factors – including access to contraception, the empowerment of women, poverty, consumerism, and the environment – apply to our population growth, now and in the future.