Major Transformations - Jaw Evolution

I like my jaws.  They are, perhaps, my favorite thing to use when I am chewing stuff.  They are also incredibly helpful in the whole talking department, and given that I am a teacher this is a fairly important adaptation for me to have.  Jaws are really swell.

But how did we come to have these neat little chompers anyway?  It turns out that the story of jaw evolution is fairly simple.  You see, once upon a time about 530 million years ago, there lived a group of critters named the Agnathans.  These were a strange sort of organism what with their long bodies and sucker faces and no paired fins, but they were some of the first fish to grace our fair ocean and for this we have to give them credit. 

They were a happy sort of fish (I assume) and lived their lives happily filtering their breakfasts, lunches, and dinners through their happy little sucker mouths.  The water would flow in through their open face hole and then out again through the gills.  This provided them with both food and oxygen which are good things to have if you want to not die.  And not die they did.  Or didn't.  Or didn't not do.  Or whichever combination of words means that they survived for quite a long time and can, in fact, be found alive today.  The relatively gross Lampreys and the downright vile Hagfish are both examples of Agnathan (jawless) fish.

Those little gills that they used to pull oxygen from the water are all feathery and frilly and, if taken out of the water, will collapse in a little less than frilly pile.  To combat this, these jawless fish used special cartilage bars called Gill Arches to give the gills a bit of backing.  These gill arches served the purpose remarkably and kept those little frilly gills open and extracting oxygen, but the relative stiffness of these gill arches could also be viewed as a bad thing.  Since they couldn't flex too much the fish had to rely on continuous movement or the occasional currents to keep water flowing over their gills.  

This constant motion was a major energy drain and could have been a bit of a problem for these early critters.  No matter how streamlined you are, constant movement is going to require more energy than simply hanging out.  If you will allow me a bit of gross oversimplification, after a bit of time a mutation or series of mutations in the genes that regulate the formation of these gill arches came about and, quite literally, changed the world.  The gill arches became hinged so that they could be a bit more flexy.  This added flexibility gave those critters with these mutations an advantage over their less flexy peers.  They could now pump their gill arches like a bellows and bring flowing water over the gills without having to move around much.

So now we have flexible gill arches.  You might be asking, What does this have to do with my ability to eat a cow?  Actually, it has everything to do with your ability to eat a cow, or celery, or anything else for that matter.  You see, it was these flexible gill arches that eventually became the jaws.

In another gross oversimplification, over time the front gill arches became more flexible and pushed forward a bit.  The flexible gill arches in the front linked up with the mouth and gave the fish a tool for trapping food.  Now the fish could flex the rear arches to bring water into the mouth and over the gills, and it could flex the front gill arches to snap completely shut to catch other critters for food.  The jaw was now basically complete - an apparatus for taking oxygen out of the water was turned into a weapon.

For a more complicated version of these events complete with fancy science words and a lot more detail, go here. 

Climate Change. It is definitely real and we are definitely causing it.

How do you know that climate change is a real thing?  That question would take a bit longer to answer than a simple blog post could handle, but take a look at these these graphics for a simplified response.  The first shows how we know the planet is warming up and the second shows how we know this is due to the behaviors of humans.  The graphics don’t make it any less cold and snowy, but they do make it a little easier to understand that a little extra cold and snow do not make climate change a hoax.

    

For more information on climate change as well as a handy guide to dealing with climate change skeptics, visit the amazing blog Skeptical Science.

Whole Genome Sequencing - It's REALLY cheap.

This graph is amazing.  When I was doing genetic research in 2003 I was able to singlehandedly ruin over $5000 worth of DNA by leaving a sample tray no bigger than an iPhone out of the freezer too long.  This did not endear me to my colleagues in the lab.  According to my calculations which I just did in my head with made up numbers, today it would require approximately an entire Apple Store worth of iPhone sized bricks to reach that value.

What this means is that the age of whole genome sequencing is upon us.  For more information on what whole genome sequencing could bring to the medical world, check out this video.        

Teaching Evolution Part 1: Increasing teacher knowledge

Last night at the Creation Museum, Bill Nye the Science Guy debated Ken Ham the Young Earth Creationist on the question "Is creation a viable model for origins?"  I don't want to spoil it for you because that ruins the fun of watching, so I'll give the answer in Spanish:  "No."

The debate over creationism and evolution has been going on for quite a while, and the legality of teaching creationism in public schools has been addressed by US courts at a variety of levels.  Thankfully, the courts have almost always sided with science and said, in no uncertain terms, that you cannot advocate for religion in public school classrooms, and creationism amounts to doing just that.  

That doesn't make evolution any easier to teach, though.  While many students are more than happy to learn about where they came from there are those that offer a bit more of a challenge.  Some students state that they don't believe in evolution but they are willing to listen and memorize things for the test.  Some refuse to participate when the evolution unit rolls around.  Others push it a bit further and engage in debates with their teachers and fellow students, often coming in with prepared remarks often given to them by parents of pastors.  Believe me - I have been given my fair share of pamphlets, Jack Chick books, and prayer cards over the years and I live in an area where this is not a major issue.  My colleagues in unnamed southern states that rhyme with “Malabama” and “Mennessee” have had whole groups of students form prayer circles in class, turn their desks around and read their bibles, and engage in mass walk-outs to protest the teaching of evolution.    

So given the fact that this subject can be controversial, how is a teacher to deal with students that find it difficult to accept the theory of evolution?  It isn't an easy thing to do for a wide variety of reasons, and in a series of posts I am going to attempt to address this by sharing the strategies that have worked for me over the years.  You may find that you have similar issues, or, should your issue not be covered here, feel free to leave a comment and I’ll tackle it in a future post.  

So lets get out of the gate here with the thing that is simultaneously the easiest and most difficult thing to address:  Teacher knowledge of evolution.

In this day and age of Common Core, state mandated testing, RTI, reading and writing across the curriculum, and the many other initiatives teachers have to deal with on a regular basis, most teachers are highly educated in pedagogy (which totally sounds like something you could be arrested for) but not as educated in the content of our discipline.  Because almost all of our inservice time is taken up learning how to implement these initiatives there isn’t a whole lot of time for us Biology teachers to further educate ourselves on content knowledge.  We all come out of college with a bachelors degree which is essentially the equivalent of a black belt in martial arts.  It seems like it is a real accomplishment, and it totally is, but it basically just proves that you have the ability to learn things and you are now ready for the next level.  It does not necessarily mean that you have mastered anything.  

As an example, I felt that I had a really good grasp of cellular respiration because I did well in cell and molecular biology and passed my tests and did well in the lab and was, in general, a ferociously amazing person.  Sometimes it physically hurt to be as awesome as I was.  When I first taught cell respiration to my students I realized that I was lacking a bit in the general knowledge department.  “Where do those NAD+ molecules come from?” inquired one student.  “Why does adding electrons to it suddenly make it NADH?” asked another.  “What, exactly, causes a cell to switch from aerobic to anaerobic respiration?” demanded yet another.  “Do you pick your own clothes out because those pants don’t go with that shirt,” said a 4th who had clearly stopped giving any semblance of a crap about cell respiration.

Aside from explaining that, yes I do pick out my own clothes and yes these pants did go with this shirt, thank-you very much, I couldn’t answer these questions.  I knew what NAD+ and NADH were, and I also knew what anaerobic and aerobic respiration were, but I had no idea how to address the specific things these kids wanted to know.  It was only after doing a bunch of research and asking more experienced teachers that I learned the answers.  Evolution is similar but can be so much worse.  When have you ever been told by a student that they don’t believe in cellular respiration?  

We all know the basics of evolution.  We know who Darwin was and all about his journey on the HMS Beagle.  We are aware of fossils and probably can name some of the cool ones like Archaeopteryx and Basilosaurus.  We can read and interpret cladograms and help the students determine a common ancestor.  But often our knowledge is lacking when it comes to the details that help transform evolution from a series of events and facts into a coherent story, and it is this story of life that makes biology amazing and comprehensible to the students.

As I mentioned before, addressing the lack-of-knowledge issue is both the easiest and the most difficult problem to tackle.  It is easy because all it takes is a some time to read books and articles, watch videos and debates, and discuss with your colleagues the things you are having trouble with.  It is also difficult because it quite a bit of time and, as already mentioned, time is not a luxury most of us have.    

To get you started on the journey, I have added links to many places where you can begin to enhance your understanding of evolutionary biology.  Some are great for classroom use while others might border on the NSFW (Not Safe For Work).  Take some time and enhance your knowledge of evolution. I'll update this list as I find/remember resources. If you have any ideas, chuck 'em into the comments and I'll add them in.

Talk Origins Archive - One of the oldest creation/evolution sites.  It has basically all of the information you will ever need to answer almost any question a student might have.  Spend enough time on this site and you will most likely never worry about teaching evolution again.

Ẅhat Next? - John Kyrk - An animated timeline of the earth showing basically everything that happened in the evolution of both the universe and the life in it.  Move the slider along and watch tiny animated atoms, fish, dinosaurs, primates and everything in between inhabit your screen.

Pharyngula - a blog by popular researcher/blogger PZ Myers.  Often irreverent and potentially offensive, but almost always worth checking out. (Occasionally NSFW for language),

Your Inner Fish - A book by Neil Shubin.  Starts off with a wonderful description of the work involved in discovering Tiktaalik and continues with an easy to read and totally informative look at how evolution has shaped the human body.  Should be required reading for anyone interested in evolutionary biology.

Understanding Evolution Website - a repository for teaching materials including activities and  labs, as well as resources for teacher education.  

Biological multiplication table

Use the above table to find out what happens when you cross a flamingo and a moose. My favorite is the squellephant. Tentacles everywhere!  

Flatworm sex

Sex.  It's how babies are made.  Whenever a student asks about sex in class I always begin my answer the same way:  "When two people/lions/jellyfish/etc. love each other very much, the engage in a special hug...(pause)...and then babies come out!"  But the truth is that not only is love not always a part of it, other individuals are not always involved.  Critters can reproduce many different ways, and students are often surprised to find that the world of animal reproduction is incredibly diverse.  

Below is an excerpt from the Zoology/Evolution text that I wrote.  It deals with one of the many methods of reproduction and it involves flatworms, or to use their correct phylum name, Platyhelminthes.  The students have already read the previous section of the chapter dealing with the flatworm's incomplete digestive system and a few other physiological tidbits, but this is the bit that I normally get the biggest response from.
  

 Flatworms can typically reproduce sexually, but they are mostly hermaphrodites which means both types of sex organs are present in each organism.  This is a great adaptation and makes reproduction so much easier.  Let me explain.  Imagine that you are a male worm and in the mood for a little reproduction.  You cruise out into your little part of the puddle in the hopes that you might meet the female worm of your dreams.  You know the kind - all flat and sexy.  Anyway, your little auricles tell you that there is another flatworm a few centimeters to your left and you begin your long crawl over to her.  On the way over you are working on your lines, fixing your pharynx so it is not dirty from your latest dinner/poop, and, in general, getting ready to mate.  When you get over to her you begin the courtship process and are immediately pushed off because the love of your life happens to be rather more male than you had expected.  You might find that you enjoy this other male's company and that you even support the same wormy soccer team, but alas, tonight is about reproduction and another male simply will not help in this matter. 

So you move on to the next worm in the pond who also happens to be male.  The same is true of the next 3 worms you try your little wormy pick-up lines on ("Hey there - I couldn't help but notice the cleanliness of your mouth/anus and I was wondering...").  Hopefully you are starting to see that it can be a bit of a problem to find a mate if the population is split into males and females.  With hermaphrodites you don't have to find a female worm or a male worm, you simply have to find another worm.  All worms are potential mates.  Not that they will all be willing to mate with you, but the possibility is there.  This is especially helpful if you happen to be a parasite and are literally stuck to a space on the intestinal wall. 

It is a little shameless self promotion, but if you like this sort of thing and are looking for something that is entertaining and informative, check out the rest of the text that I wrote for my Zoology/Evolution class at my store on Teachers Pay Teachers.  Available here.    

  

Correlation and causation

Often things appear to be connected but aren't really. For example, the sun rose after I got up this morning, so clearly I cause the sun to rise.  Just because two variables change with each other doesn't mean that one is causing the other.  This correlation-causation mixup happens all the time and the most obvious current example is the controversy surrounding vaccines and autism. For the record, there is no connection between the two, but many people are concerned of the alleged causal relatonship and have stopped vaccinating their children. 

Here are two tongue- in-cheek examples of correlations that you could use to help students understand this concept.