Hi, i think we all know the following
I have lived in Moscow for eight years. (still live in Moscow)
I had lived in Moscow for eight years, before I moved to New York. (No longer live in Moscow)
But, i got confused when I try to apply present/past pefect in following cases:
All y chromosome in existence today are descended from y chromosome of a single ancestor who is thought to have lived about 150,000 years ago (O)
All y chromosome in existence today are descended from y chromosome of a single ancestor who is thought to had lived about 150,000 years ago (X)
Since a present perfect is used when an action is continuing from the past to present, the anscestor in this case obviously no longer live till present, so my first thought was it has to be past perfect, 'had lived'.
What is wrong with my approach on present perfect in this case?
Then, for past perfect, it must indicate the action is completed before another action in the past, but since there is no other past in this sentense to indicate the action is completed before another past, we should just use a simple past as follow:
All y chromosome in existence today are descended from y chromosome of a single ancestor who lived about 150,000 years ago (Is this wrong?)
Please help and thank you in advance.
Thank you in advance.