Hi Solom, the following website lists languages by degrees of similarities in vocabulary and grammatical difficulty. how-to-learn-any-language.com/.../languages/similarities/index.html

Hello Solom, Very interesting question !:) You can check Ruhlen's "A Guide to the World's Languages" Stanford Univ. Pr., 1987). He is a leader in the new attempt to write a unified theory of language development and diffusion. There are many theories concerning this matter and they might be controversial in their very nature. Watson's theory" the Motor Theory of language" sees that at every level of language, from the elementary speech sounds, through the word-forms on to the syntactic rules and structures, language was isomorphic with the neural systems.That means they have similar appearance but are genetically different.He is more concerned with a neural organisation underlying the functions of speech and visual perception. You can read more about it here: http://www.geocities.com/Athens/Forum/2803/MotorTheoryOfLanguageOrigin.htm

There are many books. The TOPIC to search for, in English: "cross-linguistic similarities" or "cross-linguistic influence" I hope that helps you find what you are looking for.