Ch. 4: Teeth Everywhere

Please use this thread for discussing Ch. 4: Teeth Everywhere.

If they know what goes into bones to make them super hard - hydroxyapatite- why don't they start making human bones even harder? This must go against some government regulation. I wouldn't mind going back in time and havng my DNA changed around so that my bones have a little more hydroxyapatite in them. Why can't they do this for women with weak bones?

I wish Shubin in this chapter really stressed the reptile/mammalian break. I know there probably wasn't just one break but several instances where breaks manifested themselves. Listing them would have been cool. I also know that mammal/reptile is just nomenclature war but showing the gradient would have helped me to picture how one became the other.

I like how teeth seem to be the first bones ever created - to eat! Wow. Very cool to know this. Then they moved back and became a defense (scales, shell plates)! Then I guess they moved inside and became vertebrae. Now where are they going to go? hahaha Are we going to become bone people? Awesome.

Ostracoderms and conondonts were found at about the same time period - I believe 500 million years. If this is so then how could they know which came first - teeth for eating or bones for protection?

Camacho:


I believe the way they know is that conondonts only have teeth and ostracoderms have both. See the progression?

It is incredible that what makes each specie different from each other and in fact males from females is the genetic switches. I've always been fascinated by human sexuality and gender differences. I took a class in college on human sexuality (I still have the textbook, written by the professor that taught the class, Janet Shibley Hyde) and one of the very first topics we covered was prenatal sexual differentiation. All life begins as female. The only difference between a fertilized egg that will become female and the fertilized egg that will become male is the sex chromosome. The embryos of males and females remain undifferentiated until about 7 weeks post conception. At this point all the basic structures that will become the sex organs are in place. What I find amazing is that the structures are identical in males and females, until the switches (testosterone) are activated. What this means is that for every part of the male reproduction system there is a corresponding part in the female. You can match the genitalia of males to females duct by duct and nerve ending by nerve ending. Some of the structure matches are obvious, gonads and ovaries, male glans (head of the penis) and female glans (clitorides). Some not, the tissue that becomes the shaft of the penis is the same tissue in the female that becomes the lining of the vagina (all the internal duct work and the nerve networks match as well).

Interestingly, if the cells of a male (XY) embryo are androgen (testosterone) insensitive the embryo will develop into what appears to be female fetus. People with Androgen insensitivity syndrome are genetically male, but can present externally as completely female or as hermaphrodites . Actually, even more than just female - super female. These women tend to be tall, large breasted, narrow hipped, perfect complexion (high levels of testosterone is associated with acne) and facially beautiful - think super model. These women are also infertile.

Yes, this is what Shubin explains - conodonts were the most common fossil from that period - http://en.wikipedia.org/wiki/Conodont describes them and http://en.wikipedia.org/wiki/Chordata shows where they fit on the tree of life. They lived in the Paleozoic - http://en.wikipedia.org/wiki/Paleozoic Shubin's story about how scientists thought that conodonts were organisms until they found a fossil with the soft imprint of the body showed that conodonts were the teeth, which of course survived much better as fossils than the rotting flesh.

http://en.wikipedia.org/wiki/Ostracoderm shows where Ostracoderms fit.

Check out http://www.geocities.com/CapeCanaveral/ ... hatAre.htm for a good intro to conodonts and how to find them.

Shubin explains how teeth evolved - starting in conodonts as a new and efficient method for eating other creatures, and then gradually spreading. The amazing story is how ostracoderms used this innovation to build a skull as protection from other toothy eaters - the first skull was made of teeth! It is like the hand example - like the bone of the upper arm evolving to produce the two bones of the forearm, the group of bones at the wrist and then the fingers, the earliest teeth gradually evolved into the whole skeleton of vertebrates.

Ostracoderms are a great example of maladaption in practice. When fish with jaws evolved, the ostracoderm went into decline, because there was a new and better organism able to exploit its niches.

Robert Tulip wrote:



The fact that another organism develops an adaptation that is trumps another organism's adaptation does not render that adaptation maladaptive. Evolutions is a Red Queen's Race; organisms must be in a constant state of keeping up.

I have a couple Ostracoderms in my back yard and if they were to see that comment they would be pretty pissed. Don't worry, I don't let them play on my computer. Lucky for you.

No way!! Evolution is not a Red Queen's race - Through the Looking Glass is fantasy not science. The ostracoderms did not keep up which is why they went extinct. They were lumbered with an Ordovician eating system that did not have the advantage of jaws, a constraint which rendered them unable to keep up with the Devonian Red Queens (fish). Ostracoderms were adaptive for Ordovician seas, but not for Devonian. Is the word maladaptive appropriate for this? I think so. Over a long period, maladaptive features cause extinction. I think we have a few maladaptive traits in the world today, notably the instinctive willingness to expand the economy without ensuring it is ecologically safe.

Lewis Carroll had a fine sense of the absurd, but was part of an alienated English culture, like Monty Python, in which silly ideas caught people's fancy, often with a strong satirical sub-message. Like that fine evolutionary thinker, Ms Anne Elk.

Well, given that ostracoderms have been extinct for three hundred and fifty million years we can all sleep easy. Unless some of the genetic engineers discussed in Your Inner Fish manage to resurrect them ...

The Red Queen's Race is often used as a metaphor to describe evolution and the process of adjusting to a niche simply in order to stay in it (since other things are also adapting in order to better eat it or take over it's niche....).

Ostracoderms v Fish is not a Red Queens Race. Fish won. Ostracoderms did not adjust and so did not stay in the niche. Inability to adjust is maladaptive.

I never meant that the ostracoderms specifically were an example of the Red Queens Race. What I was trying to get at is traits are selected by natural selection and that all ecosystem are in a constant state of change, albeit very slow, driven by the need to keep up. There is no space for maladaption in the theory of evolution. Maladatption means that something works counter to survival. Having a bony skull is still better than not having one. It's just not as good when someone else comes along that can bite through it.

But Saffron, you seemed to use ostracoderms as an example of a Red Queens Race in arguing against the existence of maladaption, when you said, in response to my comment about ostracoderms "The fact that another organism develops an adaptation that trumps another organism's adaptation does not render that adaptation maladaptive. Evolution is a Red Queen's Race; organisms must be in a constant state of keeping up."

An interesting thing about Shubin is his description of general laws in evolution. Your comment implies that the Red Queen Race is such a general law, that organisms inevitably adapt to stay competitive. In fact this is not the case. There are often winners and losers. Humanity is now in a Red Queens Race against microbes, having to run faster to stay even. However, if a superbug evolves that causes the extinction of humanity, the race will be over.

The point about ostracoderms is that they did have a trait (lack of a jaw) which worked counter to their survival, which is why they were maladaptive and went extinct.