Well that's a good question. Some people are not believing in evolution and are asking this:
"If men evolved from apes, why are there still apes in the world?"

The answer is that we both evolved from a species which lived millions of years ago, but we were divided as separate species. I could try to explain this with an example with humans, as you mentioned the cousins.

Mary is a woman, who has two children. Mike and Bill.
Mike and Bill both find wives, get married and they have children.
Mike has a daughter called Eve, Bill has a daughter named Suzy.

Both Eve and Suzy have the same grandmother.

This is basically the same with humans and apes, however the ancestry is from grand-grand-grand-grand-grand-grand-grand..(lots of grands here)......grand-parents, from over a million years back.