Unintelligent Design: Blind Cave Fish

When discussing evolution with Creationists, I love to bring up the case of the Mexican Tetra, more commonly known as Blind Cave Fish. These fishy critters are wondrous emblems of the blind processes of evolution and prove to be conspicuous hollows in the Intelligent Design movement.

So, what are these things...?
Blind Cave Fish, are, well, blind cave fish. They are characterised by their lack of pigmentation (resulting in a pale/pink coating) and their absence of eyes. What makes them so interesting to study is that they used to have eyes, and even the die-hard YECs will acquiesce to this reality. Of course, this is due to the fact that the fish are born with partially developed ones. However, this construction soon comes to an abrupt halt, a layer of skin forms over them and the eyes disintegrate to become the useless vestiges of an image-filled past. Why, you ask? Well, that's due to their habitat: as suggested by their names, they live in caves. These caverns are dark places; devoid of lighting and rendering a set of optics as merely aesthetic accessories in its somber depths. It is thus safe to say that any orbs of light sensitive cells are now thoroughly unnecessary due to the complete and overbearing absence of light. And so, it's unsurprising to find these animals without a pair of functioning optics. To the creationist, however, it's a bit of tiffy. Why would their oh-so-immaculate designer create blind fish, with partially formed eyes, and then grow flaps over them?

Ah, so what exactly happened...?
As we have already established, the fishes dwellings are lightless environments, making navigating by light detection impossible and rendering photon-receptors irrelevant. However, they didn't always live in such conditions - which is why they still contain the remnants of their ancestors eyes (and why they begin to form in the embryo). For whatever reason, selection pressures pushed them towards caves, and there they survived and prospered, passing their genes through the generations and gradually lessening their dependence on the spherical tissue we know to be eyes.

However, the cause of the eye loss is not known with any specificity. It could be due to energy constraints or efficiency:  the formation and maintenance of an eye is quite a costly procedure. By preventing the construction of the now superfluous organs, the creature is otherwise unaffected and the energy and resources can be expended elsewhere in more useful body structures and tissues. This is called economical adaptation, and although it makes sense, it doesn't seem entirely applicable to our Blind Cave Fish. This is mainly due to the knowledge that whilst embryos, they initially develop the framework for eye construction, which later degenerate, which isn't exactly economically ideal. We can explain the messiness of this in a similar way to that of the human eye or the giraffes recurrent laryngeal nerve, evolution can't backtrack. It can only overwrite past revolutions.

Another explanation is that out of random chance, some Mexican Tetra don't fully develop eyes (due to broken genes, etc.) and this spread throughout the population despite not having any particular benefit or disadvantage. This could have happened due to the mutation that caused the eyes to cease developing being coupled with another advantageous mutation or simple genetic drift. This is referred to as being the neutral theory, but once again - it doesn't seem to be a satisfying explanation. The Blind Cave Fish don't have broken genes, and according to PZ Myers, "transplanting a lens from a cavefish species with eyes to the blind cavefish embryo is enough to rescue the eye, which then develops into a perfect and functional visual organ."

There is another solution discussed here, which is based on based on pleiotropy and developmental interactions. You can look those up elsewhere.

And so, we don't know with certainty that exact details of the transition - but we know that it happened. It could have been for any of the above reasons, perhaps even them all playing some role, as well as to simple factors such as how the eyes consist of delicate tissue which has a potential for injury and possibly infection. Despite not knowing the specifics (how could we?), we have a general understanding of the concept and we can recognise the fingerprint the fragmented processes of natural selection have left us. 

The Creationist response...

...is quite hilarious. They initially assert that such anomalies don't comply with evolution, because, apparently, evolution can only work towards complexity. This is just willful ignorance and anyone who spews such garbage has absolutely no idea what they're talking about and deserve nothing but laughter. I shouldn't even bother explain this, but here it is: evolution is just adaptation. It goes whatever the hell way is necessary. Whether that be a progression to complexity or a regression to simplicity doesn't matter in the least. Suitability to the environment is all that matters.

Or, the Creationist misses the point entirely by stating the fish work perfectly for what they do. Duh. The point is they still have the remnants of eyes. With all that unnecessary baggage and energy wastage, this Creationists designer isn't very eco-friendly.

Another is just a case of severe intellectual dishonesty. In this article, a creationist tries to dismantle the correlations between evolution and the Mexican Tetra. It only reinforces the veracity of the process.

For instance, the author or the article actually outlines natural selection at work whilst trying to explain how the "Curse" caused copying errors which eventually resulted in the eyeless fish.

"The eyed fish would thus have a lesser chance of surviving to produce offspring. Those fish carrying the ‘eyeless’ genetic defect would have a greater chance of passing it on to the next generation, so it would not take many generations under such circumstances for all the fish to be of the ‘eyeless’ type."

Yeah, that's natural selection in a nutshell, and given enough time, will inevitably lead to complex or more adapted structures. 

"It is not showing us how the first stages of a new, complex adaptation could arise" 

Oh yes, the "no new information" non-argument, as outlined and refuted here (and in countless other locations). Regardless, evolution works both ways, it doesn't matter what way you look at the process. If a system can mutate, this mutation will interact with other genes etc., which will result in novel combinations and thus, novel material. Whether this causes a reduction in overall complexity or whether it causes a progression towards more complex structures doesn't matter, it is still the same process at work.
___

Sorry for the length of this one. I don't know what happened.