Of course it doesn't. But if you are making claims that a particular feature is adaptive in a specific way, you had better be able to provide some evidence for

Of course it doesn't. But if you are making claims that a particular feature is adaptive in a specific way, you had better be able to provide some evidence for it - and one way of doing this is showing the trait being adaptive in a different population in the same ecological niche, or having an explanation as to why not, or being able to somehow rule out the other dozen perfectly plausible reasons as to why the trait exists. Not every phsysiological trait has to be adaptive.