Update: Many thanks to Chris for reminding me of one of my most favorite SNL sketches;
In March I blogged about a Malaysian woman who claimed to have found a shark with webbed feet, although anyone with even a cursory knowledge of shark anatomy could see that the “webbed feet” were really the paired male reproductive organs indicative of sharks known as claspers. [Not that I expect others to have this understanding, but rather that it’s obvious if you do have that knowledge] Now the story has resurfaced, probably due to it being featured on this blog, and plenty of folks are blathering away about how the shark does or does not support evolution. Apparently this has become the evolution equivalent of the New Zealand “plesiosaur” mix-up, at least among evolution supporters who are woefully uninformed. I was content to keep my mouth shut about this issue, just letting the issue fade away into obscurity, but then I received this comment from “bnutler”;
yeah but the first feet probably were not “feet” either. the process of evolution involves mutations, and this is an example of a mutation could have lead to feet. it would be unintelligent to assume that the first feet were actually intended to be used in the way land animals use them. It would be even more unintelligent to think that something hand designed everything on earth..
This is why the evolution debate frustrates me; even amongst people who support evolution, understanding can be absent. Tetrapods did not evolve their limbs from paired claspers; the bones of our limbs (and the limbs of our ancestors all the way down to the first tetrapods) are homologous with those of fish belonging to the Class Sarcopterygii, an extant example being the Coelacanth. The living coelacanth is not ancestral to us however, as it is too young in age and belongs to the wrong group. The group that led to tetrapods were the Rhipidistia, a subgroup of the Sarcopterygiian fish, and it was the bones in the fleshy fins of these animals that gave rise to the tetrapod limb. Indeed, even though living coelacanths are not our ancestors, they give us a clue as to how fins could have been modified to limbs; in addition to having the proper structure, they can “walk” through the water using their fins, moving them independently. Epaulette Sharks can walk along the bottom as well, using their pectoral and pelvic fins, although their skeletons are a long way from being anything close to that of the Rhipidistians.
Anyway, shark claspers are only found in male sharks, and although they are supported by cartilage they are not otherwise connected to the spine or skeleton. Thus, in order for claspers to be the antecedents to feet, they’d have to become present in all sharks of that species (including females), somehow change their musculature, change their skeletal structure, allow attachment to the rest of the skeleton, and also duplicate themselves in the front part of the skeleton and undergo the same changes (unless you’re going to argue that claspers made the back feet and pectoral fins made the front feet). This is obviously ridiculous, and furthermore what is being suggested by bnutler is a major saltation; a major change from having paired reproductive organs to having feet overnight (it would bring a new meaning to foot-fetishes, I’ll tell you that much). This isn’t even mentioning all the other physiological changes that would have to occur in the body (which we have evidence for in tetrapod evolution, especially in the spine and skull), and overall sharks are an extremely poor candidate for tetrapod ancestors, then or now.
I don’t mean to be so overly harsh, but I simply cannot believe all the back and forth over this picture. If anything, it’s a lesson that it’s not simply enough to get people to agree that evolution has occurred; if they do not understand it no good will come from it. Without understanding, people will have “faith” in evolution rather than knowledge of it, and even if a school isn’t teaching ID or creationism it doesn’t mean that they’re teaching evolution accurately (or at all!). I especially liked bnutler’s ending sentences, wherein he (she?) insinuates that because I don’t agree that the shark claspers are really freaky feet, I must believe that limbs were “intelligently designed” or created for a purpose. I guess they don’t stop by here much, huh?
[Update: Changed some of the language as it was a bit harsh; such comes from blogging out of frustrations. Also I was writing feverishly using the Mac at home, which does not highlight spelling/grammatical errors, which I have now fixed as well.]