Thread: What is the smallest a human population can be before extinction of the whole species is likely?

Without inbreeding and other such acts.
I am writing and need a scientifically backed number.
This is for a work of science fiction in which the human population world wide has dropped dramatically (and there is a reason very evident in the work from the get go, I am just choosing not to say here). I am having trouble finding the numbers myself and did know them off-hand at one time.

Inbreeding would be the major obstacle to a population rebound in the face of some type of major global disaster. As far as the number of people required you have to ask how many people (a million is still a pretty small part of 6 billion) and how wide they are spread. If you're talking 30 people in one group to repopulate the planet then yes there will be difficulties but dispersed pockets of a hundred or so people would be ok providing they had adequate food and fresh water to stay healthy. That is of course providing that they are all not too close genetically to start with but 100 should be decent with the right mix of genes.