Excerpts indented from this article at the New Scientist:
One of creationists’ favourite claims is that an organ as intricate as the eye could never have simply evolved. Fresh evidence to the contrary has now arrived, courtesy of a creature related to jellyfish.
The tiny freshwater hydra has no eyes but it will contract into a ball when exposed to sudden bright light. David Plachetzki and colleagues at the University of California, Santa Barbara, have found that hydras “see” light using two proteins closely related to those in our own eyes.
“If you look at something as complex as an eye, you might be at a loss to explain how the whole structure evolved at once,” says Plachetzki, now at the University of California, Davis. “But if you look at its components you can start to piece together how it happened.” That’s especially feasible now that genes from the earliest animals, such as the hydra, are being sequenced.
Rod and cone cells in the human retina contain proteins called opsins that change shape when light strikes them. This causes another type of protein, an ion channel, to generate an electrical signal along nerves connecting the eye to the brain – a process called phototransduction.
Hydras have the same types of opsins and ion channels as we do.
Why? Why does a critter with no eyes have the same opsins and ion channels as we do? According to creationists, the ‘explanation’ is that god made the freshwater hydra this way, an explanation empty of meaning because it is empty of evidence to inform it. “God made it this way” is an unverifiable assertion, an assumption that the hypothesis is true without any means to test that truth claim. “god made it this way” is not a meaningful explanation because it provides no meaningful answer. Its explanatory power is zero, the equivalent of a null set. Many people think that this null set approach is legitimate ”science’ (creationists call it by another name in the world of scientific education: Intelligent Design, a term substituted into newer texts from older creationist tracts to present a different more modern face to this very old theological belief). Proponents of ID pretend that some ‘force’ must have produced the complexity we find in nature, making it, they claim, a legitimate alternative scientific theory to evolution without also proving us an explanatory framework within which we can find various ways and means to produce testable, verifiable, falsifiable, and predictable causal and correlational answers informed by evidence rather than meaningless assertions of supernatural intervention and divine design based on an assumed belief that such an assertion is true. On this scientific scale, ID is theological creationism repackaged and re-branded.
The theory of evolution offers an explanatory framework in which we can deduce that because both humans and freshwater hydras possess the same opsins and ion channels, we therefore should share a common ancestor. Critters who have different opsins and ion channels should not.
If biologists accepted this assertion and assumed that the word should means the same thing as the word does, without any further investigation to inform the assertion, then they would be open to the legitimate charge of merely holding a different belief than creationists. But real scientists don’t stop their investigations with assertions and simply assume them to be true. Real scientists must inform their hypothesis with something more than assertions and assumptions… a little thing called evidence. In the case of the freshwater hydra, real biologists ask the important question How might we determine, even indirectly, if we do share a common ancestor? and then attempt to account for any evidence that supports or refutes the hypothesis.
One avenue of investigation: as already mentioned, gene sequencing.
Plachetzki’s team then built a family tree of opsin gene sequences from 22 highly diverse creatures, and found that opsins in hydras and humans evolved from those in a common ancestor. Another line of descendants from the same ancestor gave rise to somewhat different opsins and ion channels in insect and mollusc eyes. This supports other indirect evidence, says Nilsson, that the hydras’ light-sensing equipment was the original model, and the insects’ came later.
The hydra is the most primitive animal with functioning opsins, so the team concludes that it represents “the very origin of animal phototransduction”, which was incorporated into more complex eyes as they evolved.
This finding is more evidence of the power of explanation that the theory of evolution offers us. That god made insect eyes to rely on a mutated version of the opsins and ion channels common to the freshwater hydra and humans is no explanation whatsoever answering the related question of why they are different so-called ‘designs'; using the theory of evolution, we do find an explanation that accounts for the evidence. The theory works. Again.
To those who promote creationism as an alternative explanation so beautifully explained by evolution’s overwhelming multi-branched mutually supporting natural evidence as just a different way to ‘know’, who wish to teach the next generation of citizens that a belief that offers no meaningful explanation is as good as one informed by one that consistently does, I say Shame. Shame on you for choosing to promote your supernatural beliefs as if they were equal methods to the harder but more rewarding obtainment of real knowledge through informed biological science. Shame on you for equating that the two explanatory approaches are equal in the quality their respective inquiries. They’re not, you know it, and you as the responsible adult and parent and citizen should know better than to lie to children to soothe your conscience in maintaining your superstitious beliefs as a legitimate but different kind of attainable knowledge about the natural world when it is no such thing: creationism in all its disguises that answers questions with “Because god made it so” is an unjustified belief in the legitimacy of supernatural causation. The explanation contains no evidence in which to inform it. Foisting that unjustified belief on the next generation masked as an equally valid scientific theory, implying without cause that there actually exists some imaginary scientific controversy, is an exercise in promoting and teaching willful ignorance.