A complete discussion of copyright law is beyond our purpose here at "Tip of the Day," but suffice it to say that a genealogical fact cannot be copyrighted. Your cousin in Arizona cannot copyright the fact that "John Smith was born in Maryland in 1783."
What he can copyright is a report he compiled showing why that year of birth is correct. The report he would be within his rights to lay copyright claim to.
Of course, if he spent years uncovering a fact and you use that fact in a compilation, it might be nice to give him credit for "finding" that fact. If you don't, he might not share anything with you again!