Another example of convergence found in human and squid eye genes

We have to start this post with the definition of convergence in biology.

In evolutionary biology, convergent evolution is the process whereby organisms not closely related (not monophyletic), independently evolve similar traits as a result of having to adapt to similar environments or ecological niches.

It is the opposite of divergent evolution, where related species evolve different traits.

On a molecular level, this can happen due to random mutation unrelated to adaptive changes; see long branch attraction. In cultural evolution, convergent evolution is the development of similar cultural adaptations to similar environmental conditions by different peoples with different ancestral cultures. An example of convergent evolution is the similar nature of the flight/wings of insects, birds, pterosaurs, and bats.

All four serve the same function and are similar in structure, but each evolved independently.

With that being said, here is an article from Real Clear Science with me. (H/T Melissa from Science, Faith and Reason)


Eyes and wings are among 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 squid and humans. Exactly how such convergent evolution arises is not always clear.

In a new study, published in Nature Scientific Reports, researchers have found that, despite belonging to completely different lineages, humans and squid evolved through tweaks to the same gene.

Like all organs, the eye is the product of many genes working together. The majority of those genes provide information about how to make part of the eye. For example, one gene provides information to construct a light-sensitive pigment. Another gene provides information to make a lens.

Most of the genes involved in making the eye read like a parts list – this gene makes this, and that gene makes that. 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”.

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 squid to you and me. This means the Pax6 gene predates the evolutionary diversification of these lineages – during the Cambrian period, some 500m years ago.

I asked Melissa if this was another example of “convergence”, and she said it was. That’s because the gene is present in animals that DO NOT SHARE A COMMON ANCESTOR. In short, this is exactly identical to the case where a computer programmer reuses the same library of functions in two completely different programs. For example, using the Apache CXF web service library to create two completely different REST-like web services with two completely different clients. (Which is what I am doing at work right now!).

This example of convergence makes no sense on naturalistic evolution – you can evolve the same gene so many times in animals with no common ancestry. It screams out design. See the related posts below for more examples of convergence, and remember that the more we know about science, the more difficult the problem becomes for a naturalist.

Related posts



4 thoughts on “Another example of convergence found in human and squid eye genes”

  1. There are common ancestors. It’s explicitly mentioned in the material you quote. If the lineages split, they have a common ancestor. A very distant one, but quite possibly one that already had Pax6.

    If (big “if” right there) it didn’t, then depending on the complexity of the gene, it could be a real mathematical long shot, quite possibly enough to defy explanation under current theory.

    “This means the Pax6 gene *predates the evolutionary diversification* of these lineages – during the Cambrian period, some 500m years ago.”

    Who told this girl humans and cephalopods have no common ancestor? That’s crazy. She just made it up. They’re both animals. They’re both *alive*. What are we, progressives here, that we just say whatever pops into our heads that furthers the Cause? I thought you guys believed your position was objectively true?


    1. First, you’re just asserting there is a common ancestor, because your religion forces you to. You don’t have the evidence to back your view up.
      Second, if you are talking about the common ancestor being prior to the Cambrian, that would be a single-celled organism – not an animal.
      Third, what are your qualifications? The person who wrote this writing on Science Daily. My blog is awesome, but it’s not Science Daily.

      You have to be careful not to assume what you are trying to prove. If you think that two things that are alive MUST have a common ancestor, then you’re begging the question. The issue is common descent. You can’t assume it. You have to show the data. You haven’t got it. That’s the problem.


    2. The argument for convergent evolution in this case isn’t so much that humans and cephalopods don’t have a common ancestor, but that they couldn’t have gotten this particular gene from a common ancestor. The problem is that JUST these two organisms have this same gene, even though they are not closely related, while their close relatives do not. The issue isn’t just that they have the same gene, but that all the other organisms thought to be closely related to them and “between” them (so to speak) in the evolutionary chain do not.

      What it comes down to is that there are two insurmountable problems IF humans and cephalopods got their version of the Pax6 gene from a common ancestor:

      1) The common ancestor (if there was one) would be very far back in evolutionary history. This would mean that an advanced version of a master control gene for an advanced image-forming eye was present in a very simple pre-Cambrian organism. That is too implausible to be the case.

      2) This version of the gene is not present in other organisms that are thought to share common ancestry with humans and cephalopods. In short, as you look across the spectrum of living things, you have two organisms that are very different and have almost no similarities, but who, inexplicably, have this one very specific similarity. The idea that this one feature has been lying dormant throughout eons of evolutionary history and billions of individuals in both of their ancestries, just to pop up in these two incredibly different creatures is beyond all rationality.

      Thus, the only possible answer (in an evolutionary scenario) is that this gene has evolved separately in two completely different organisms. That is why convergent evolution is being proposed. The idea is that the gene evolved in humans and evolved in cephalopods, but those events were completely unrelated.

      Of course, the convergent evolution scenario is only slightly more plausible than having the feature come from a common ancestor. Which is to say, not at all plausible. To have such a complex feature evolve through undirected natural processes even once strains the limits of credulity. That it should happen more than once is downright ridiculous. Thus, common design forms a far better explanation for this observed similarity than any evolutionary scenario.


      1. Thanks so much for this excellent comment, Lindsay! I appreciate that you know more about this issue than I do, and this is a great answer. I appreciate you taking the time to write it.


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