hybrid life...

look at the genome of a sea squirt and you'll get a nasty surprise. half of its genes have a straightforward evolutionary history. in fairness, so does the other half. trouble is, the two histories are completely different. it seems that sea squirts do not, as we had thought, sit among the chordates, on the same evolutionary line as humans and other vertebrates. instead, they are the result of what happens when you fuse an ancient chordate with the ancestor of a sea urchin. the fusion of two distinct evolutionary lines is not supposed to work. according to received biological wisdom, any chimeras that result are meant to be evolutionary dead ends. not for the first time, received wisdom appears to be wrong. "there was a view that hybridisation was bad, and 'pure' species were good," says james mallet of university college london. the truth is, hybridisation is like mutation--mostly it's bad, but occasionally it throws out something that meets a need. "natural selection can use whatever inherited variation comes its way," mallet says. biologists are now coming round to the idea that much of nature is not a product of neat family lines, but a messy mass of cross links. that may be how, for instance, genetic instructions can turn something like a caterpillar into something completely different: a butterfly// michael brooks, 09.02.09, new scientist