Descendants of the Prophet
It is possible that every human being now alive is descended from the Prophet and anybody in his time who has descendants today.
A mathematician did the calculations, although they are much debated.
One thing is certain: if two individuals have no common ancestor, than they belong to different species.
Evolution says we all have common ancestors, microbes, humans, trees, etc.
The real question is at what point in time did our most recent common ancestor live? Also, at what point in time do all of the people who have descendants today become the ancestors of all of the people alive today (sorry is that is not a very clear statement). This is a moving target.
I know that I am descended from all ten of the ten most prolific ancestors in French Canada, which means I probably share at least one ancestor with any French Canadian of old stock. In a similar manner, the early settlers of New England, English Canada, etc., have millions of descendants, all related somehow or other, without knowing how.
A child born in 1945 would have about 2,000,000 ancestors around 1200-1250. That would be about two thirds of the population of the British Isles.
My British ancestors are, in all probability, common to many hundreds of thousands or millions of people of British Stock, although some homebodies probably don't share my French ancestors, and only thousands of British people have any chance of sharing a French Canadian ancestor--probably an Acadian exile, some of whom ended up in Britain, or a French Huguenot who fled to Britain in 1685 because of religious persecution.
The Mayflower Pilgrims of the 1620 are estimated to be the ancestors of more than 8 million Americans and another million people in Africa, Asia, etc. Sailors do get around.