I am glad Andy Jones has weighed in on this topic; he is incomparably better qualified than I to comment on the Hackett, et al. article in Science. I would just like emphasize one general point from the point of view of (and for the benefit of) birders, who are generally not closely acquainted with genetics. Nor am I for that matter, I just happen to have a talented step-daughter who is a geneticist and patiently explains things to me from time to time. First, many of the birders who have weighed in on this topic tend to confuse phenotype and genotype. This is the old "if it walks like a duck and quacks like a duck, it must be a duck" school of thought that dates back to before Linnaeus. Unfortunately, biology is replete with examples of things that look very similar, but which are genetically quite distinct, and vice versa. The key objective in taxonomy is to find an objective measure of the differences between organisms. In the nineteenth century, it was thought that morphological measurements, properly arranged, would disclose the relationships between groups of living entities. By and large, they pretty much got it right, but problems remained. Sibley and Ahlquist's DNA-DNA hybridization studies of the 80's were a big step forward and led to some deep insights into bird relationships. However, the DNAs of two different species can hybridize in a gazillion ways and each way will have a different dissociation temperature. The resulting noise in the measurements limits the resolution of the distinctions that can be made. The newer nucleotide sequencing techniques are based on the question "how many substitutions would I have to make to turn this gene into that one?" If many substitutions are necessary, the species must not be closely related. As Andy points out, 19 nuclear loci is a huge advance over most studies. By contrast, the genetic "bar coding" project that stirred up so much buzz two years ago used no more than 600 base pairs on one locus of the mitochondrial DNA. The Hackett study is an enormous advance in resolution, but it too leaves some unanswered questions. Andy mentions the time-honored conundrum of the Hoatzin, the bizarre South American bird that clambers around in trees using the claws on its wings. The new study also cannot confidently place the pigeons and doves, a widespread and numerous family known to just about every human on the planet. So the search goes on. With faster sequencers, better statistical methods, and bigger computers, we may one day be able to answer these questions. Then we can move on to defining just what a species is and how come those ducks and gulls hybridize so easily. For those of you who can stand a little more depth, I recommend Devorah Bennu's blog http://scienceblogs.com/grrlscientist/2008/06/early_birds_shake_up_avian_tre.php for a nifty synopsis of the Hackett paper, including some nice graphics that dramatically illustrate the relationships between the clades. Cheers, Bob -- Robert D Powell Wilmington, OH, USA [log in to unmask] http://rdp1710.wordpress.com Nulla dies sine linea ______________________________________________________________________ Ohio-birds mailing list, a service of the Ohio Ornithological Society. Our thanks to Miami University for hosting this mailing list. Additional discussions can be found in our forums, at www.ohiobirds.org/forum/. You can join or leave the list, or change your options, at: http://listserv.muohio.edu/scripts/wa.exe?LIST=OHIO-BIRDS Send questions or comments about the list to: [log in to unmask]