MP-Ryan, I wouldn't mind hearing an explanation of what these guys actually discovered.
OK, a little background: the entire developmental lineage of C. elegans (one of the nematodes under study) is mapped. There are an exact number of cells in every adult, and we know exactly where they came from. You can trace the worm from single-cell to adult through its cell divisions, which is an extremely useful tool for studying developmental genetics, and subsequently developmental evolution.
More background: Believe it or not, not all species develop the same organs in the same ways. There's a rather famous example that plagues developmental biology students everywhere. Humans, chickens, zebrafish represent three very different vertebrates. During the first hours of embryonic development, they all look the same but their gene expression patterns are wildly different. In early development, they all look wildly different but their gene expression patterns are virtually identical. Mid-way through development they all look very much the same, but their gene expression is totally different again; and finally, in adulthood they not only look different but their gene expression patterns are totally different. Why? Because there are conserved genetic and physical stages of development, necessary steps which MUST occur to produce a healthy organism. Gene expression always preceeds the physical result, which is why we see the pattern we see. But the point is that we can produce the same systems in different ways, as long as certain essential points are reached.
This study goes a step beyond that - they are looking at the evolution of developmental systems in these worms. And what they've found is that the observed differences in how the worms produce their vulva (the vulva is essentially the same in adulthood for all of the species) are not random; random mutations do not account for the variance in vulval system development, but rather the system tended to evolve directionally in certain ways, partially depending on the presence or absence of selection pressure. The hypothesis they've partially discredited believed random mutations accounted for the variation in development of the vulva - that is, the development of the system would vary quite widely with the end result being the same. This paper says no - the system as a whole tends to evolve along very specific lines, which can revert and converge. Thus, developmental systems are evolving in a directional manner rather than a purely random one.
It forces a re-thinking of the problem I mentioned earlier in vertebrates, because the conventional wisdom is that only certain stages of each developmental pathway are required, whereas this is suggesting that, on a system level at least, the pathways themselves evolve as a whole and that individual elements are not simply subject to isolated changes. The whole pathway is pushed in a certain direction, even though the end result of it remains the same. Essentially, their phylogenetic analysis showed that certain pathway patterns tend to show up which can be traced in an evolutionary lineage through selection, rather than merely the result of random changes to the development of the vulva in each species.
Bottomline: If we see a different developmental system producing the same vulval structure in different worms, it's due to selection pressures acting on each developmental system which bias the direction of change, and not simply the accumulation of a series of random mutations within the system that have no impact on the end result.
I hope that explains it. I've been re-reading the article and I'm still trying to wrap my head around it myself, so I imagine my explanation here isn't all that clear. Kudos to you if you can decipher it.
For anyone with journal article access, here is the reference information:
Current Biology 17, pp1925–1937, November 20, 2007
Trends, Stasis, and Drift in the Evolution of Nematode Vulva Development
Karin Kiontke,1,* Antoine Barrie` re,2 Irina Kolotuev,3
Benjamin Podbilewicz,3 Ralf Sommer,4
David H.A. Fitch,1 and Marie-Anne Fe´ lix2
...and honestly, all you have to do is look at the title to see that the Slashdot article author was apparently on crack.