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The librarian could not believe it. On the doorstep was a package. It was a plastic bag. Inside were two old books. There was a note that said: "Happy Easter".

But the books were not just any books. They were diaries kept by Charles DarwinHis book, On the Origin of Species by Means of Natural Selection, is the founding work of evolutionary biology.. 

The notebooks have been missing since 2001. They were stolen. Now, somebody has given them back to Cambridge UniversityOne of the UK's top universities. It was founded in 1209. . 

Charles Darwin was a scientist. He made the theory of evolution popular. The theory says that living things change over time in order to survive better. 

For a long time, scientists thought evolution was a bit like a family tree. They thought that species are descended from older ones that die out. 

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But this might not be true. One expert thinks species do not just die out and create new species. Instead, they can mix together and merge. 

If this is true, lots of Darwin's ideas could be wrong. We are not part of a big family tree. It looks much more like a spider web with lots of connections! 

Yes! Experts today can study many more species than Darwin. They see that evolution is not as simple as we thought. We are all interconnected in different ways. 

Not really. We might have come from some other living species. But Darwin's basic idea is still true. A tree is a better way to imagine it. The whole world cannot be connected through a web.