Musa corms

Jim McKenney
Mon, 04 Jun 2012 08:47:00 PDT
I'm too busy to get into this discussion now, but I'm sooooo tempted. So I'll add this: one of the reasons attempts to define structures can be so difficult is that the structures in question often evolve separately. A useful distinction is the distinction between analogous structures and homologous structures.

Analogous structures, although apparently similar, do not share a common embryological/evolutionary history. The wings of insects and the wings of birds are analogous structures: we call both wings, but these structures have distinct embryological/ evolutionary histories. I've never met anyone whose sense of language propriety is so refined that they felt it an error to call both wings, even though they were very aware that they had nothing in common except an apparent function. 

Homologous structures on the other hand share a common embryological or evolutionary history, and that they are of common origin is often not at all apparent. For instance, our teeth and the rough material in shark skin share a common embryological origin - they are homologous structures. Our finger nails and the horn of rhinoceros share a common embryological origin and are homologous structures. 

True bulbs and bulb-like structures occur in both monocots and dicots: almost certainly they evolved separately in these groups. But the concept of deep homology might account for their origin. 

But even when all is said and done, when all the definitions have been screwed up as tight as possible, there will always be this: try as we might, it is virtually impossible to speak or write without being to some degree metaphorical.  

Jim McKenney

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