Should I join my to be advisor if he has a background in a very different domain, in evolutionary biology, than my research interests like genomics, machine learning, predictive modeling, systems biology, and cancers?

He says that he is recruiting me so that I can work on cancers. He has some great ideas about evolutionary biology and cancers but no prior experience in what I'm currently doing or wish to do.

He insists that I'll be free to continue what I'm doing or do something related which I'm interested in. So, would it be wise to join him considering his background is entirely different? I have no affinity for evolutionary biology.

Note: I've another offer from a university where I can do lab rotations and then pick up on my advisor.

Sometimes different backgrounds can be good as you can pick up ideas that you may not have thought of otherwise. I think if you know what you are doing and know the techniques you are using then it's fine, but it's very difficult if you don't as your supervisor won't have a clue either.

If you are getting freedom to research whatever you want that is a pretty sweet deal though.

The impression I get is that many of the skills and attributes of a good supervisor are general academic and quite transferrable. They should, of course, have a good general knowledge of the wider subject area but you are the expert in your own PhD. As my supervisor told me, if your supervisor knows more about your topic by the time you complete the degree, there's a problem. Questions to ask yourself, and possibly some of his other supervisees if you can: (1) does he have a good track record in publishing (2) Can he steer you through the minefield of academic life including publishing, teaching etc.? (3) Does he have the time to devote to supervision? Some of the best supervisors on paper are very, very busy people; and (4) What's your impression of how you'll get on with him? Some people may disagree, but I think personalities count when you're trying to build and sustain a positive professional relationship dynamic in a situation like this.

Anyway, these are my two cents - maybe post again to let us know what you decide to do?