<em>Et Tu</em>, Octopus? It Was Hard Enough to Explain Human Eyes by Unguided Processes - Evolution News & Views

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Et Tu, Octopus? It Was Hard Enough to Explain Human Eyes by Unguided Processes

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Malcolm Campbell must feel at least a tinge of embarrassment for his proposal in The Conversation that the same "stunning innovations" in nature evolved not just once, but multiple times independently, here specifically in vertebrates and cephalopods. A hint of that embarrassment surfaces in the last sentence of his first paragraph:

Eyes and wings are amongst the most stunning innovations evolution has created. Remarkably these features have evolved multiple times in different lineages of animals. For instance, the avian ancestors of birds and the mammalian ancestors of bats both evolved wings independently, in an example of convergent evolution. The same happened for the eyes of squids and humans. Exactly how such convergent evolution arises is not always clear. (Emphasis added.)

Is it ever? Campbell, writing about a paper in Nature Scientific Reports, "Cephalopod eye evolution was modulated by the acquisition of Pax-6 splicing variants," has to tackle genetic convergence along with functional convergence. Let's see if this instance is clear (without assuming Darwinian theory, that is).

Campbell agrees that "the eye is the product of many genes working together." Eye construction is more than just a "parts list" (although some genes work that way, generating single parts).

But some genes orchestrate the construction of the eye. Rather than providing instructions to make an eye part, these genes provide information about where and when parts need to be constructed and assembled. In keeping with their role in controlling the process of eye formation, these genes are called "master control genes".

Sounds good for design theory so far. Master control; informational control; this corresponds pretty well with irreducible complexity and hierarchical organization, features of designed systems. It doesn't sound compatible with unguided processes. But then --

The most important of master control genes implicated in making eyes is called Pax6. The ancestral Pax6 gene probably orchestrated the formation of a very simple eye -- merely a collection of light-sensing cells working together to inform a primitive organism of when it was out in the open versus in the dark, or in the shade.

Today the legacy of that early Pax6 gene lives on in an incredible diversity of organisms, from birds and bees, to shellfish and whales, from squids to you and me. This means the Pax6 gene predates the evolutionary diversification of these lineages -- during the Cambrian period, some 500m years ago.

Now that he has this one "master control" gene timed before the Cambrian explosion, he feels free to let it orchestrate any work Darwin puts on the playlist: compound eyes of bees, whale eyes, squid eyes, and human eyes. Pax6 just had to wave its arms; the instrumentalists show up and make the music.

In order to create such an elaborate structure, the activities Pax6 controlled became more complex. To accommodate this, evolution increased the number of instructions that arose from a single Pax6 gene....

RNA code is interesting in that it can be edited. One kind of editing, called splicing, removes a piece from the middle of the code, and stitches the two ends together. The marvel of splicing is that it can be used to produce two different kinds of instructions from the same piece of RNA code. RNA made from the Pax6 can be spliced in just such a manner. As a consequence, two different kinds of instructions can be generated from the same Pax6 RNA.

Design advocates know all this and see it as evidence for design. Campbell, without blinking an eye, tells us that RNA splicing in Pax6 "has been used to create a camera eye in a surprising lineage.... the lineage that includes squid, cuttlefish, and octopus -- the cephalopods." The paper he references actually says very little about evolution. It certainly doesn't explain how this one gene could "create a camera eye." On the contrary, they conclude:

In summary, we identified the acquisition of splicing variations of Pax-6 in cephalopod eyes ... and found that the acquisition occurred independently in vertebrates and cephalopods. These Pax-6 splicing variations in cephalopods were controlled spatio-temporally during eye formation. Although the acquisition of camera eyes in the cephalopods is yet a problem, Pax-6 variants in cephalopods have been acquired in a lineage-specific manner.

Strictly speaking, scientists have only found uncanny similarities in vertebrate and invertebrate camera eyes. Those similarities involve a particular master control gene, Pax6. But think of the problems for Darwinian evolution: whatever that gene did in the Precambrian oceans (perhaps "orchestrating" a light-sensitive spot), it had to get an instant PhD in orchestration to manage the compound eyes in trilobites and other animals that suddenly appeared in the Cambrian explosion. Then, tens of millions of years later on the branch leading to cephalopods, it had to "create a camera eye" that is a wonder of nature in squids and octopus.

But then -- without any possible cross-communication -- another Pax6 gene on a completely separate branch leading to vertebrates had to learn to create a camera eye all over again.

Cephalopods have a camera eye with the same features as the vertebrate camera eye. Importantly, the cephalopod camera eye arose completely independently from ours. The last common ancestor of cephalopods and vertebrates existed more than 500m years ago.

A reasonable observer should be astonished at the brashness of such claims.

Pax6 RNA splicing in cephalopods is a wonderful demonstration of how evolution fashions equivalent solutions via entirely different routes. Using analogous structures, evolution can provide remarkable innovations.

Ah well, for those who refuse to consider intelligent design, it's a familiar song and dance.

Photo source: DaugaardDK/Flickr.


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