And occasionally, they switch genders altogether. My first name, Haven, was considered to be an unusual male name when I was growing up. Now it's considered to be a unusual (but rapidly gaining in popularity) female name due to its' usage.
again many thanks everyone - this is the first time I've ever researched a name in detail - so trying to get my head around the issues. Thanks for the responses. (and Siri - had never heard of the name Haven for either a girl or a boy - it's beautiful). Cheers. E.V.