Evelyne
maybe there's something i don't understand about it. I mean, okay, maybe we all have a
*common* ancestor from such recent times but, surely, there are people with ancestors that go further back? And it's just that those ancestors aren't also the ancestors of all other people alive today?
When we refer to something as a common ancestor we have to be careful here. I'm not affluent in the specifics of evolutionary biology such as the names of the different species but I do understand the theory of evolution.
This is actually one the most talked about issues and least understood ones at the same time, by non-scientists anyways. You have to keep in mind that evolution occurs because there is imperfect replication of the genes whenever they are made as gametes. Such imperfections is what allowed us humans to look like what we look like today. If this replication process was perfect then we surely would have died off as a whole and no animal would even be seen on this planet to this day.
Now that's out of the way, when we refer to common ancestor we have to place a frame of reference on it. This is not an absolute term as you can imagine but has to carry context.
Now take a look at the phylogenetic tree on the right, pay no attention to the tree on the left. But as you can already probably see there are a lot of points on this tree that could be called common ancestors to the species. Three such examples are (X), (A), (Z). This is self explanatory but I can take that you can see that (B) and (C) share a common ancestor (X) and (B) (C) and (D) share a common ancestor of (Z).
I hope this clears up the common ancestor thing for you.