Your Inner Fish – Chapter 3

Handy Genes

The story of our relationship to fossil animals is not just based on anatomy.  It can also be seen in our genes.  Those sequences of DNA that make us who we are.  Indeed makes every living thing what it is.

Shubin’s lab is divided into two parts.  One to study fossils and one to study DNA and embryonic development.  For these two things go hand in hand (if you’ll forgive the pun).

This chapter is pretty thick and a summary will be difficult, so bear with me if this gets long.

We all know that DNA is what makes us what we are.  What we’re not always sure about it how.  So, while Shubin was in the Arctic, another researcher in his lab was busy injected a form of Vitamin A into shark and skate embryos.  Why?

To quote Shubin

Our limbs exist in three dimensions: They have a top and a bottom, a pinky side and a thumb side, a base and a tip.  The bones at the tips, in our fingers, are different from the bones at the shoulder.  Likewise, our hands are different from our thumbs.

How does our body know to develop this way?

In short, it has to do with concentrations of chemicals produced by the cells in our our developing body.  All of the genetic switches that control this do their thing between the third and eighth week after conception.  Yep, before most women even know they are pregnant, the basic structure of the embryo is already set up.

What researchers in the 50s and 60s found was that a certain patch of cells was responsible for all of the limb development.  Remove that patch and no limb develops.  Turn the patch of cells over and the limb grows backwards.  Cut the patch in half and you end up with two limbs.  Note that this was all done on chickens.

Later, geneticists working with flies discovered a gene they called hedgehog.  This gene controlled which end of the fly was which.  This was very similar in concept to the patch of cells that controlled the orientation of the limbs, so the researchers went looking for this in other creatures.

They named the chicken version of the gene (which is surprisingly similar to the fly version) Sonic hedgehog.  Yes, after the video game.  But what did it actually do?

With a neat trick that allows the region of the body that Sonic hedgehog is active to glow, the researchers found that gene was only active in those cells that I mentioned in limb development.

Interestingly, the form of Vitamin A that was mentioned previously causes Sonic hedgehog to activate.  So by injecting Vitamin A, one can control the development of limbs in a chicken embryo. It’s easy to make double wings for example or mirror wings (top and bottom).

It gets even more interesting, because every limbed creature on the planet has the Sonic hedgehog gene.  It is effectively the same in everything and it can be controlled by vitamin A injections.

In fact, the same gene is present in sharks and skates, which are very primitive versions of sharks.  In fact, the vitamin A injections work exactly the same in sharks and skates, resulting in changes in how the limbs develop.

The researchers went a step farther and injected a small amount of the protein that Sonic hedgehog makes into the developing limb of a shark embryo.  Except that it was the protein from a mouse. If the mice gene is too different from the shark gene, nothing will happen.  If the mice gene is very similar, then it will affect the limb development in exactly the same way as vitamin A injections.  Anyone want to guess what happened?

Yep, the mouse protein injection had the same effect on the shark.  This means that the protein and therefore the gene are effectively the same in a shark and a mouse.  How’s that for evidence of common descent?

What does all this mean?

I’ll let Shubin speak again.

What does this mean for the problem we looked into in the first two chapters – the transition of fish fins into limbs?  It means that this great evolutionary transformation did not involve the origin of new DNA: much of the shift likely involved using ancient genes, such as those involved in shark fin development, in new ways to make limbs with fingers and toes.

Now, I’m sure that creationists will pipe up with all the things we don’t know.  Of course, if we knew everything, then scientists would be out of a job.  However, research like this is just stunning, especially compared with the research that creationists are doing…

And this shows a stunning example of common descent.  If the exact same gene controls limb development in everything from sharks to humans, then it is a much more parsimonious explanation that we all had a common ancestor.

Click to see the rest of the entries.

This entry was posted in Book Review, Creationism / ID, Education, Evolution, evolution, Science and tagged , , , , , . Bookmark the permalink.

5 Responses to Your Inner Fish – Chapter 3

  1. Pingback: Your Inner Fish – A Chapter-by-Chapter Review | Cassandra's Tears

  2. Joe G says:

    So the evidence for a common design is now evidence for common descent?

    How did evolutionary processes- ie an accumulation of genetic accidents- cobble together regulatory networks? IOW what is the evidence that such a thing is even possible?

  3. ogremkv says:

    Joe, I’m not sure how much simpler I can make this…

    Even if you disprove evolution, right here, right now and every scientist on the planet agrees with you. It still doesn’t mean that Intelligent Design is correct. The only thing that will do that is positive evidence for ID. You don’t have any. As evidence in this blog, your own blog comments, and every other forum on which you post, you cannot provide that evidence. Because there isn’t any.

    You can’t even explain why ‘intelligence’ is required in the intelligent design notion, other than a built in bias to need a god-figure. There is nothing, not a single requirement of the Intelligent Design notion that can’t be exactly the same in a Design notion.

    The simplest proof of that is, as we said, intelligently designed systems don’t have to be complex and non-intelligent systems can be complex.

    As far as evidence for “regulatory networks”. Why don’t you give us an example of such a network. While you’re doing that, cite the papers that describe the evolution of the network you choose. That way, at least we know you’re doing your homework. While you’re at it, why don’t you find an expert on that system and ask him about the evolution of the system?

    I know why you won’t do any of that, because you have a built in bias and you refuse to learn anything that doesn’t meet your expectations.

    As far as the ‘evidence for common design’. Isn’t it interesting how the evidence for common design is EXACTLY THE SAME as evidence for evolution. In other words (cause I know how you love that phrase, even though you can’t use it properly), Intelligent Design is non-discriminatory. It cannot be used to choose between itself and evolution, because you think it’s the exact same thing. Your only problem with evolution is that you can’t understand how it happened, therefore you think it was designed. Unfortunately, that’s a fallacious argument (but you know that already).

    It’s a shame that you can’t hold your own notions to the same standards that you require for evolution. But that’s what you get from someone who is so biased.

  4. Joe G says:


    ID stands on its own and ID is not anti-evolution-> that is if you listen to the experts/ authorities on both sides.
    Also it is a requirement that ID goes through the premise that all is reducible to matter, energy, chemistry and physics.

    And yes we have explained why a designer is required.

    And there aren’t any papers that demonstrate an accumulation of genetic accidents can produce regulatory networks- that is networks that control other networks such as HOX genes and other tools in the genetic tool-kit.

    The problem is your position doesn’t have any evidence to support its claims. all you have is imagination.

  5. ogremkv says:

    Joe, I tire of this. Which of course means that you think you win. Whatever it is that you win. It certainly isn’t fame, fortune, or a Nobel.

    1) You are the only person on this planet who thinks that ID is not anti-evolution. I provided you with more than a dozen instances of the people you venerate (Behe, Dembski, and Meyer) all saying, specifically, that ID is anti-evolution. You can’t see it because it goes against what you think and you have failed to progress beyond a 4-year olds understand of the universe. Just I think something is true, doesn’t make it true. I’m truly sorry that you are like this, but I can’t help you with that. All I can do is continue to show how you are wrong in the hopes that others will think.

    2) I don’t even understand what this sentence means “Also it is a requirement that ID goes through the premise that all is reducible to matter, energy, chemistry and physics.” Perhaps if you could write more clearly, then you could think more clearly… or vice versa.

    3) No you have not explained why a designer is required. You have stated what you think are reasons a designer is required. But you (and all other IDists) have failed to deal with the simple fact that non-complex non-intelligent processes can develop complex systems and structures, by any definition you care to use for complex. Until you deal with that, then you will never be able to declare that an intelligent designer is required. This is, of course, for some value of intelligence. You are the person who decided that termites are intelligent after all.

    4) Why don’t you give me a ‘regulatory network’ and we’ll see what we can figure out shall we? If I have time and can be bothered. Regardless of whether I do this or not. Regardless of whether I find out that there is significant evolutionary framework behind such a network or not. It still have no bearing on the simple fact that Intelligent Design still has no supporting evidence.

    5) You don’t even know what my position is Joe. You claim to know all about evolution, then you trot out strawman after strawman. What’s really funny is that everyone here, AtBC, etc all agree that there is no evidence for the version of evolution YOU give. Of course, that’s not the version of evolution that anyone actually uses, so you’re pretty much wasting your time on a snipe hunt.

Comments are closed.