FizRoy船长遗憾第一次航行时没有博物学家跟着去而错误了做出科学发现的机会，所以希望这一次有个博物学家一起考察，同时做为一个gentleman同伴。做为一名够格的博物学家是上船的必要条件。Henslow被海军部要求推荐一名博物学家，他在给达尔文的信中写得很清楚，他是因为认为达尔文是个够格的博物学家才推荐他的："I have stated that I consider you to be the best qualified person I know of who is likely to undertake such a situation -- I state this not on the supposition of your being a finished Naturalist, but as amply qualified for collecting, observing, and noting anything worthy to be noted in Natural History."