Questions - The role of language contact in creating correlations between humidity and tone

This paper is a reaction to Everett et al., 2015.

1. How many languages are there in the world? How many are tonal (with simple or complex tones)? How many tones can a language have?
   Hint: Answers to these questions are not in the paper, but should help us to put the paper in context. Either guess or check Wikipedia and WALS.

2. What is the conclusion of Everett et al.? How strong are the stated correlations?

3. What are Collins' objections against the Everett et al. paper? Are there any potential confounds or other issues with the Everett's tests that can be identified?

4. What is the point of the simulations in the paper?