Who's related to who and why does it matter?

 Model of USNM 1100247, Macrocheira kaempferi, from Japan.

Model of USNM 1100247, Macrocheira kaempferi, from Japan.

Who is it related to? That's a question I've been asking about spider crabs for years. DNA is helping me solve that question so I can ask the next question: "Why is it important to know who it is related to?" My answer to this is that trying to study biological patterns in unrelated crabs is akin to comparing apples and oranges. If I wanted to study decorating behavior in a family of crabs where half the crabs were more closely related to crabs in other families those crabs may show wildly different behaviors that obscure the pattern that is held by the crabs that actually are related to each other. But if I can only compare crabs that we know are closely related based on DNA analyses, then I am better able to test hypotheses about those crabs. I'm already seeing patterns in geographical distribution and habitat type that have only emerged since grouping crabs based on DNA rather than the traditionally used morphological characters. Perhaps knowing who is related to who will help us understand the underlying drivers of crab diversity. As far as I'm concerned, knowing who is related to who is just the beginning. The real fun starts when we can answer that question and I'm ready to start asking all those next questions. So who is that big, beautiful Macrocheira kempferi up there related to? Well, you'll just have to wait to find out.