Why science definitions matter: a response to the NCSE’s Misconception Mondays

Dear fellow scientists and science educators: may I suggest the time has come to work together to standardize the major terminology of our field?  I don’t mean the terminology of specific disciplines, I am getting at the fundamentals here: what is science, and how do we effectively and efficiently communicate what a hypothesis, law, and theory are?

I am writing this post because I read with some dismay the recent National Center for Science Education’s blog Misconception Mondays: Hypotheses, Theories, and Laws, Oh My! by Stephanie Keep.  I encourage my readers to read her blog post and form your own opinions.  I want to be clear from the beginning that this is nothing personal about Stephanie Keep — her post simply caught my attention and serves as a spring board for discussing what I read and hear all too often from many of my colleagues.

The take home message from Keep’s post is this: it doesn’t matter what labels we give concepts in science, so long as science is being taught.  In essence, don’t get bogged down in semantics and lose the forest for the trees — it is more important that students understand the science.  At face value, this seems reasonable: don’t be pedantic be practical.

On deeper reflection, however, this attitude (an attitude shared by many in the sciences) is troublesome, because definitions and the meanings we attach to words do matter, especially for students and the public who vote on science issues.  Keep says:

People—especially scientists—like firm definitions. Science is full of technical terms that we learn to master (or learn to quickly look up on the Internet), and thanks to a mixture of precedent and state standards, many teachers keep making kids learn definitions for theory, law, and hypothesis in the introductory weeks of a new class. I’m not suggesting that kids shouldn’t learn what a hypothesis is—of course they should! Forming and testing hypotheses are fundamental parts of any scientific endeavor. But I am suggesting that we be willing to admit that there is often no good reason why something is called a law vs. a theory, or a hypothesis vs. a theory—and that’s okay.

But therein lies the fundamental problem with this approach — not just Keep’s approach, but, I would argue, the approach so many of us have been taught to take.  How can you teach a student how to test a hypothesis if you simultaneously tell them that we can’t tell if it’s a hypothesis or a theory?  These definitions do matter.

Something else is troublesome in Keep’s statement that, “many teachers keep making kids learn definitions for theory, law, and hypothesis in the introductory weeks of a new class.”  In any discipline, you learn what it is and how it works in the beginning so that you have a common language through which to teach and make sense of the core material.

If we are charged with doing science and with educating the public about science, shouldn’t we able to say: here is what science is, here are it’s limits, and here’s how the toolkit works?  Especially at the beginning of a class?  As scientists and science educators, we seem on the whole to be so circumspect about this because, I suspect, we appreciate that science is not about certainty but about probability.  Therefore, we are loathe to say we have a concrete definition because we fear that what we convey is an absolutism rather than messy reality.  Believe me — I understand and appreciate wanting to avoid teaching our students that science = unassailable truth.  But if this is a fear of looking too authoritarian, in my opinion, it has led to much confusion both among ourselves and the public at a time when science is under attack.

Dear scientists and science educators: it is okay to have firm definitions that define and describe what we do, and we need to give ourselves permission to be okay with that.  It is no longer okay for us to say to students, in essence, we can’t really describe or define what it is we do precisely, but you’ll know it when you see it.

It would be arrogant and presumptuous on my part to suggest I have the definitive answer or definitions for what we do, nor do any of us work and teach in a vacuum — much of what I teach my students is cobbled together from what I have found works for me as an instructor (borrowed and morphed from many gifted individuals), particularly the approach of a former graduate mentor, Dr. Ron Toth at Northern Illinois University.

But I would like to start a conversation about fundamentals.  Surely, science as a discipline is not an amorphous thing.  I suspect most of us would define it as a tool for understanding the natural world.  Many of us test hypotheses – these are predictive statements that can be tested and falsified which guide our research.  We often test our hypotheses under an explanatory umbrella we call a theory.  As an example, a paleontologist might test the relationships of various dinosaurs (a hypothesis called a phylogeny) using data collected from fossils, working under the explanation that they are closely or distantly related through common ancestry (a theory called biological evolution).

Laws, I will admit, often stick in many of our craws.  I have come to see scientific laws as testable descriptions of repeatable phenomena or processes.  If we define scientific laws in this way, we are now more clear about what should qualify.  For example, in her essay, Keep says,

Have you ever noticed that most of the “laws” in science tend to be in the physical sciences and astronomy? There aren’t a lot of “laws” in biology—in fact, I can’t think of any aside from Mendel’s Laws. Why is that? Is it because biology is a “soft science” while physics and astronomy are “hard sciences”? Not at all. It’s because people in those fields really liked the term “law.” No, really. That’s pretty much it.

I would argue that we do have laws in all the branches of science, we just don’t always call them that.  If a scientific law is a repeatable phenomenon or process, Genetic Dogma (DNA is transcribed and translated by RNA into proteins) is a law — it happens continuously in all living things, always the same — a repeatable phenomenon or process.  Natural Selection is a Law — all individuals vary, more individuals in a population are born than can survive, and those with variable traits that allow them reproduce viable offspring are “selected.”  Look at any population in the living world, and this process is on-going and repeatable.  How about calling the Cell Theory, the Cell Law?  After all, that living things are made of cells is pretty much a repeatably observable phenomenon.

This works for me and for teaching my students, but I am not suggesting I have the market cornered on this definition.  Rather, my point here is that when we have a clear definition, we can more easily comprehend what we are communicating to one another and to our students.  If I am testing a hypothesis, you and others know I am probably working under an explanation, a theory.  If I am testing a law, you and others know that if I find variation or the phenomenon does not repeat, I may be in a position to reject or modify that law.

We need to have this conversation because definitions do matter in science.  What you call something does matter, especially when you need it to convey a particular set of qualities.  True, there will always be exceptions to the definitions and the natural world is messy, but don’t let perfection be the enemy of progressScience is and should be definable — we don’t just know it when we see it.

I welcome any constructive feedback and ideas from all of my colleagues as to how we can and should move forward.  I want to thank Stephanie Keep for sparking this conversation.

For those who don’t know and who might be interested, I have outlined and explained my own approaching to teaching science and evolution.

Why I Believe Bill Nye Should Not Debate Creationism

If you are not already aware, Bill Nye (the Science Guy) and Ken Ham (founder of the Creation Museum) are scheduled to have a debate at the Creation Museum on February 4, 2014.

This debate was apparently triggered by a video posted by Bill Nye entitled, “Creationism is Not Appropriate For Children” on YouTube.  Not to be undone, Ken Ham posted his own response with embedded links to two other Ph.D.s who amplify his belief that evolution, not Creationism, is damaging to children.

If the goal is science education, then I believe this debate is a poor way to improve the reception of science education in the general public.  Why do I feel this way?

There is a poor or nebulous definition of evolution and science by both parties.

In his video, Bill Nye states, “Evolution is the fundamental idea in all of biology.”  I really like Bill Nye, but I’m sorry, Bill.  Evolution is not an idea.  It is a scientific theory.  If you’re going to have a debate about science, definitions become hugely important.  A scientific theory is a testable, falsifiable, and predictable explanation of natural phenomena.  If you couch evolution as an idea, you open the door to a debate about ideology, not science.

Of course, Ken Ham has science wrong as well. He says, “Science means knowledge – you can divide science into historical science … and observational science.”  No on both fronts.  First, science as it is practiced is not a definition but a method — specifically methodological naturalism.  It is the tool by which we understand the natural world — a narrow discipline, in fact, that seeks to pose answerable questions about nature.  Second, science is science.  All science is based on observations at some level — the dinosaur bones may not “come with labels on them,” but they are observable data that can measured, studied, and so forth.  So, there is not observable versus historical science — it’s all the same thing.

A scientist works under a theory, an explanation for some type of phenomenon in the natural world, to test hypotheses.  If you work on chemistry, you are working under (among other theories) the atomic theory which states that all matter is made of atoms with specific properties.  Until recently, chemists have done a bang up job of testing and predicting chemical reactions and their consequences without seeing directly into atoms.  That’s because the testable explanation (atomic theory) was effective for inferring what should occur.  So, to say that evolution is “historical science” which is “beliefs about the past” is a gross misconstruction of how science works.

When Ken Ham says, “If evolution were true … it would be so obvious to the kids …” he is ignoring the fact that many applicable theories of science are weird and not obvious.  For example, the theories of general and special relativity predict that time is experienced differently by different objects at different speeds and in different gravitational fields.  If you use satellite technology, those satellites whizzing in orbit around the earth have clocks that quickly go out of synch with those on earth (which is explained by the theories of relativity) and thus we have to take special measures to synchronize them with our devices on the earth (GPS comes to mind).  That is good science but not something particularly obvious to kids.

In a nutshell, science is like the honey badger of internet lore — it doesn’t care about your beliefs or opinions.  Data drives what is accepted and rejected.

We are again fighting a metaphysical clash of civilizations.

Based both on what Bill Nye and Ken Ham say, this debate is not about data.  A scientific debate would be about data.  Instead, we have what amounts to, in my mind, another metaphysical clash of civilizations.  Ken Ham and his organization are very clear on this.  He is not concerned about data, but rather showing that “Creationism teaches children that they’re special, that they’re made in the image of God.”  In that one statement, you have what is actually being debated spelled out: whether or not you believe in a particular deity in a particular way.  This is why Ken Ham, his organizations, and others like him make the leap from teaching evolution to teaching kids they’re “just animals” to gay marriage and so forth.

However, Bill Nye is not doing anyone a favor by saying, “In a couple of centuries that world view [creationism] will not exist … there’s no evidence for it.”  Nye has basically indicated that, yes, evolution is a world view, but it is supported by evidence.  And if that is true, then it follows that in this metaphysical clash of civilizations you have to pick a side.  At least, if you follow Ken Ham and his compatriots, that is likely what you are led to believe from such statements.

There is No Clear Distinction About Faith and Creationism

I have said this before, but it bears repeating – there is no conflict between science and faith.  Yet, that is precisely what this debate is already boiling down to.  Science is not faith – it is a tool for understanding the natural world.  Faith is a deeply personal set of beliefs that often cannot be demonstrated scientifically, but that makes them no less valid to the individuals that hold them.  This is not my idea, not by a long shot, but to rephrase the words of many who have come before me, science and faith are after separate goals.  You don’t scientifically test faith, and you don’t apply faith where science works well (the natural world).  This is why they can and should coexist — they serve different purposes, often to the betterment of us all by people with noble intentions.

But the Creationism of Ken Ham and the Creation Museum is not mainstream Christianity.  Many Christians from many faith traditions accept science and evolutionary theory while maintaining their faith.  Ken Ham wants you to conflate his narrow concept of Christianity (a fundamental, literal interpretation of a particular version of the Bible) with Christianity as it actually exists in the world.  But that conflation works to his advantage, because if we are choosing camps, and you identify as a Christian, you cannot “believe” evolution because a humanist (whatever that may mean to you), Bill Nye, is coming after your faith.

A Plea and Some Thoughts

No one person holds all the keys to our problems, so I would never be so bold as to say I have the answer.  Here, then, is my plea and a few thoughts.

I think what many scientists, myself included, are troubled by is hucksterism and charlatanism — snake oil salesmen dressed in religious or authoritarian garb using ignorance to fund their own ambitions and power.  But it is vitally important that we do not conflate that clear and present danger with faith overall.  Given that a majority of Americans identify as people of faith, broadly lumping them in with extremists serves no one and is very damaging.  My plea to my scientific colleagues is, stop doing that.  This is just as damaging as saying that people with no religious beliefs are evil, wrong-headed, and trying to subvert American culture.

As I have said before, fear, not data, is the bottom line here.  People are afraid that their faith is being attacked — once you are afraid, data (the currency of scientists) doesn’t really matter.  What scares people about science?  What scares them about evolution?  How, as scientists, do we work with the majority of people who can see the benefits of science as a tool but are afraid to compromise their spirituality?  That, to me, is the challenge of our time.

You will not convince those with extreme convictions to self-reflect and re-evaluate.  You can bring oceans of data and heaps of observations, but it will do you no good, because the debate is not really about science but about fear and emotion.  So, if Ken Ham and his followers are convinced they are right, having a debate only ever further convinces them that they are.  Do you really think Ken Ham would ever take the results of the debate as anything but a win if not just great publicity?

My last thought or plea: don’t debate Ken Ham and other so-called Creationists.  There are people convinced to their core that the world is flat – no amount of data and debate will sway them, and nothing much will be accomplished.  But they, like Ken Ham, do not represent the majority.  The majority is who we desperately need to reach.  Certainly, when such extremist views threaten to undermine science education, we should and must push back as the National Center for Science Education has admirably done.  That is very different, however, from going out of one’s way to have what will amount mostly to spectacle and the reinforcing of deeply held convictions on both sides.

Again, I like and respect Bill Nye a lot, and I think he has done wonders for science education in the United States. To Bill Nye and any other well-meaning scientists out there who want to improve science education, please do not debate Creationists — this is not the way to accomplish what we all want.

Apparently I’ve gone viral -or- Stick figures and evolution

I came back from teaching an introductory biology course yesterday (Friday, Sept 13, 2013), to find a whole lot of messages from friends and family waiting for me on Facebook.  It turns out, unbeknownst to me, that my stick figure evolution cartoon was picked up by I F**king Love Science and went viral!

Stick figure evolution, by me — an illustration I use to explain to my students and lay audiences how evolution is not a straight line but a family tree of life. This went viral on IFLS: https://fbcdn-sphotos-g-a.akamaihd.net/hphotos-ak-prn2/1185649_635460856485590_1073680004_n.jpg

First, I am honored — honored that anything I did would even remotely reach this kind of an audience, and honored that IFLS found it worthy.

Second, please keep in mind this is intended to be fun, simple, and, above all, a diagram.  I submitted it for a Stick Figure Science contest back in 2010 for Florida Citizens for Science: http://www.flascience.org/ss2010top10.html   I was pleased at that time that it made the top 10.  So, this cartoon of mine has been out and about for a while.  It was quite surprising to see it “discovered” and shared so rapidly just now.

Third, the comments section under this cartoon has been interesting to read.  I wanted to tackle some of the recurrent themes here and put to rest any misunderstandings.

First, I will tackle the whole relationship aspect of the questions:

  1. There a lot of comments that suggest the human family tree is wrong — that I should have aunts and uncles where I have cousins.  The confusion here seems to be the conflating of “relatives” in a general sense and common ancestry.  Certainly, you share DNA with your aunts and uncles, and no doubt they descended from your grandparents.  But remember – your have aunts and uncles on your mom’s side and on your dad’s side.  Therefore, they are related to your parents and to you, but they are not your direct common ancestors.
  2. Regarding your relationship with your cousins – the only direct common ancestor you have with your cousins are your maternal and paternal grandparents.  Why?  This is because, unless there is a lot of close family intermarriages, your aunts and uncles, from which your cousins are descended, likely married someone not related to them.  So your cousins share some but not all of their DNA with you and your parents.  To find a common ancestor – a group of people whom you and your cousins could all call blood relatives – we have to look to your grandparents.
  3. Regarding second-cousins — as it turns out, there are many colloquial and law-based ways in which this word is used.  When I made the cartoon, I was simply thinking of the children of your great aunts and uncles, to which you would share a last common ancestor with your great grandparents.

Now, I want to clear up biological evolution and comments related to how I drew the “family tree”:

  1. The point I am making with the cartoon is that if you can appreciate that you have descended from common ancestors you call your parents, grandparents, and so on, you can understand biological evolution at it’s most basic level.  Darwin said that biological evolution is a theory that explained the diversity of life because of “Descent with modification” from a single, common ancestor.  All living things on earth, and all those we find as fossils, are/were part of a great family tree of life.  That is the sum total of what biological evolution means to a scientist.
  2. Saying you “evolved” from a cat or chimp or whatever else is as incorrect and ridiculous as saying your morphed from your dad to you.  No serious scientist would accept that.  But saying that we have a closer common ancestor with other mammals, like a cat, than we do with a salamander is what the data support.  As an example, the theory of biological evolution predicts there would be a common ancestral population of mammals from which all of we milk-giving fur balls have descended.  But no monkeys are mutating into humans, I promise.
  3. I stress BIOLOGICAL EVOLUTION – that is because the word “evolution” means a lot of things and is used in various ways to describe change over time, star development, the development of cultural ideas, etc.  BIOLOGICAL EVOLUTION strictly means “Descent with modification from a single, common ancestor.”

Finally, there has been a “fishes” controversy:

  1. Please keep in mind that our common use of words doesn’t always apply in science.  Theory is a great word that outside of science means a guess or hunch, but in science a theory is a powerful tool – an over-arching explanation of laws, hypotheses, and observations that can be tested, falsified, and has predictive power.
  2. Yes, yes, I know — we were all scolded by our English teachers that “fish” is singular and plural.  Except that in biological and paleontological science, “fish” is, well, “fishy.”  Based on common ancestry, for example, we humans are highly derived bony fish!  Why?  Because we share homologies with everything that has an internal bony skeleton that set us apart from non-bony backboned (vertebrate) animals.  Sharks are a type of “fish,” technically called chondrichthyans; the fish we consume tend to be ray-finned bony fishes or actinopterygians, etc.  In science, it is perfectly acceptable to use the term “Fishes” to acknowledge that “Fish” is not a catch-all for everything with fins, scales, and gills.  Don’t believe me?  Fine, see Berkeley’s evolution website right here: http://evolution.berkeley.edu/evolibrary/article/fishtree_01

Still confused?  Please remember that what you were taught in high school for biology is often simply a list of beasties with name tags — the good old Linnean classification system: Kingdom, Phylum, Class, and so on.  The Linnean system is fantastic for being a universal labeling system, but it does not often reflect evolutionary relationships, just as your name and family name don’t always accurately reflect your DNA and actual ancestry.  Why else would National Geographic and other entities be so popular at tracing people’s lineages through DNA?  Modern biology and paleontology use a tool called cladistics which focuses on unraveling relationships through special, shared traits called homologies — however, most of the non-career-science public is not familiar with this science, and that understandably causes confusion.

Finally — yes, technically what I have drawn in the cartoon are over-simplified cladograms.  They still reflect the fundamental principle of BIOLOGICAL EVOLUTION — a family tree of life, descent with modification from a single, common ancestor.  If you can communicate this family tree concept to a lay audience with stick figures even more elegantly in a single panel, I would love to see it and cherish using it in my teaching and outreach.

If you want to learn more, I have a whole audio series and other “resources” on evolution.

Understanding Science & Evolution Podcasts “Remastered”

Just a short post to note that my audio podcast series, Understanding Science and Evolution, has had a makeover.  Now the audio files are mastered in better quality audio and my new institutional affiliation is reflected in them.

Many of you who follow my blog have probably heard these before, but I hope these new, “remastered” podcasts find other listeners.  If you know anyone who might enjoy these or find them useful, please pass it on.

Oh, Rats!

Dr. Bonnan and three undergraduates at the Richard Stockton College have begun to investigate the forelimb anatomy of the white lab rat (Rattus norvegicus).

This mammal is well-known and has been the center of many studies, but we would now like to take what is known about forelimb locomotion into 3-D by using XROMM technology in cooperation with Brown University.  Currently, three undergraduates are working on different aspects of rat forelimb anatomy, and each will scan and describe the three-dimensional morphology of bones in the rat forelimb.  This summer (2013), XROMM data collected by Dr. Bonnan at Brown will be analyzed in conjunction with the undergraduate students and their long bone scans to reconstruct forelimb movements related to pronation in white rats.  Why are we doing this and what does this have to do with dinosaur locomotion?

Radha Varadharajan
Student Radha Varadharajan dissecting rat forelimbs – she will focus on describing movements of the scapula.
Kadeisha Pinkney
Student Kadeisha Pinkney – she is dissecting rat forelimbs and will be describing the contribution of the humerus to pronation.
Evan Drake
Student Evan Drake – he is dissecting rat forelimbs and will focus on the contribution of the radius and ulna to pronation.

We will begin blogging and tweeting about our lab’s work in the near future … stay tuned!

Dead dinosaurs and reasons for hope

“Time will turn us into statues, eventually.”

– Saint David Grohl, a fighter of foo

As we enter this time of the holidays in the United States, many of us become reflective on the year and take stock of our lives.  For my family and I, this year has been absolutely wonderful, dreadful, fantastic, unnerving, scary, and hopeful.  Why?  There has been a lot of change in our lives: see my lonely post from September for more details and my farewell to my previous institution.  This would also explain my dearth of blog posts, although a weird and interesting topic snuck in this November.

I am also finishing my dinosaur course here at Stockton, and that means I give my final lecture on “What I hope you have learned from dinosaurs.”  It struck me today that this would make an excellent little blog post as well.

One of my grandfathers was fond of asking me, “Why study dinosaurs?  What’s the point?” When you are asked that question enough times, you eventually develop a repertoire of answers.  I don’t know if these ever satisfied him, but I do hope they satisfy those willing to listen:

There are the Big Picture Reasons:

  • First off, dinosaurs are just so damn cool.  Those who need convincing haven’t been paying much attention to the plethora of amazing discoveries that have continued at an ever-accelerating pace since the late 1800s.
  • Dinosaurs put our place in the world into perspective – this is not a world meant for us, but one we have had the happy fortune to inherit from previous generations of life.
  • Dinosaurs were the most successful group of terrestrial vertebrates the world has seen … and they are still among us as beautiful, feathered treasures.  Oh, birds are not dinosaurs?  Like the Honey Badger, the data don’t care … and the support for birds as dinosaurs is as overwhelming as the data for humans as mammals.

And then there are the Practical Reasons:

  • Dinosaurs are the perfect ambassadors for science – they bring scientific concepts and the nature of science to children and the public like nothing else I know.
  • While the doctors and veterinarians of the world are busy saving those people and pets you love, the vertebrate paleontologists are in the trenches at the universities and colleges, teaching the next group of practitioners their anatomy.  That’s right – most vertebrate paleontologists are excellent anatomists.  A certain Larry Witmer comes to mind …
  • Want to understand why vertebrate anatomy is the way it is?  Ask a vertebrate paleontologist – we have to know all that embryology and evolution stuff to inform our research and to blow your mind. =)  The bottom line has always been the anatomy is the result of embryology and evolution … who better to teach that we dinosaur-o-philes?  And so that I’m being fair – all vertebrate paleontologists are this excellent, not just the dinosaur ones!

Yes, you say, but we’ve heard these platitudes before.  You spoke of hope … where is that?  If dinosaurs have taught me nothing else, it is an appreciation for human life.  As successful as dinosaurs were, their Encephalization Quotient (their EQ, or brain size) was never too generous.  We mammals, on the other hand, have had the evolutionary fortune of inheriting a rather different brain with a typically much higher EQ.  To be fair, the birdy dinosaurs around us have enlarged brains compared to their predecessors.

Why is EQ size a reason for hope?  Well, EQ by itself is not, but it is what we Homo sapiens do with it that is.  I am no anthropologist, but speaking in general terms, here are two things one can say about humans that cannot, so far as I know, be applied to other vertebrate animals:

  1. We can both anticipate the future and act on it.
  2. We can use imagination to bring positive things into concrete existence.

For all of their significance and success, the non-avian dinosaurs could not have anticipated their demise, nor could they have done anything to act on it.  Apart from ancient aliens imbuing dinosaurs with a sense of imagination (I can imagine a particular channel of history losing all its credibility), these mighty animals could not have brought forth everything from medicine to concepts of social justice.  As a species, we are certainly still working on a lot and have a long, long way to go, but have you ever stopped to think of how unbelievably special and unique it is that we can act on knowledge and create our future?

So this holiday season, and throughout the year, I hope you may reflect on the fact that whereas for non-avian dinosaurs history’s lessons were inaccessible, they are very much an open book for us.  If we can anticipate what the future will bring, we can act on it.  If we decide to put our imagination to good use, we can create positive change in the world.

The non-avian dinosaurs could not learn from their past, but perhaps we can learn from them … and from our own ancestors.

“So have a toast and down the cup, and drink to bones that turn to dust.” — Oingo Boingo (Danny Elfman’s rock band)

Danny Elfman, creator of the Simpson’s Theme Song, can’t be wrong …

References

Fastovsky, D. and Weishampel, D. 2009. Dinosaurs: A Concise Natural History. Cambridge University Press. 379 pp.

Penis worms, anuses, and evolution

Now that I have your attention, what is a penis worm?  Technically, they are invertebrate animals called priapulids which, if you know your Latin, has the word “penis” in there.  What exactly are they?  They are sausage-shaped, segmented worm-like animals with an extensible, toothy proboscis they use to capture prey.  Here is what a priapulid looks like:

Priapulus caudatus

A priapulus “worm” — the proboscis is pointing up in this picture.

What do these weird-looking and rather unknown animals have to do with evolution?  A whole lot, as it turns out.

The group of creatures we call Animals is incredibly diverse, and most of us have only a passing familiarity with a small fraction of these denizens.  It turns out that once you get past sponges, jellyfish and their kin, and a weird band of animals called comb jellies, there is a great clade of animals called the Bilateria.  Sounds formal, but basically the name means that this group of animals is bilaterally symmetrical – that is, these animals have symmetry about their midline and have right and left sides.  Look in the mirror – congratulations, you, too, are a member of Bilateria!

File:SymmetryOfLifeFormsOnEarth.jpg

The diversity of Bilaterian animals.

You may not appreciate it, but one of the key developments of bilaterian animals is forming a distinct mouth and anus.  This involves the formation of a gut tube, and like all tubes it has to start somewhere.  That somewhere is a puckered indentation called a blastopore that forms early during their embryonic development.  Yes, even we humans develop a blastopore as the beginning of our gut tract.

Among the bilaterian animals, there has traditionally been a split proposed that divides these organisms into two groups based on a fundamental difference in the way their digestive tracts develop.  In one group called Protostomes, the blastopore becomes the mouth, and the gut tract develops until it “punctures” the other end of the animal, forming the anus.  The word Protostome means “mouth first.”  Protostomes include a huge variety of animals such as insects, crustaceans, earthworms, mollusks, and most other “creepy-crawlies” you are familiar with.

In the other group, called Deuterostomes (meaning “mouth second”), the blastopore becomes the anus and the digestive tract stretches from hind to fore, eventually “punching” through the head region to form the mouth.  As I like to tell my students, Deuterstomes develop from the bottom up – you may now groan.  Something that may make you groan all the more is the fact that we vertebrates are members of the Deuterostomes.

File:Protovsdeuterostomes.svg

The development of the mouth and anus in Protostomes and Deuterostomes.

What does all this have to do with Priapulids?  Everything.  You see, the big evolutionary question is which came first, Protostome development or Deuterostome development?  Which is the original condition in the common ancestor?  Knowing this would inform our understanding of how other changes in development downstream from this evolutionary event were effected, and what we should predict to see in various animal lineages.

So, in a recent study by Martin-Duran and colleagues (2012) in which they followed the development of this engimatic worm, they found … drum roll … that priapulids develop as Deuterostomes, with the blastopore forming the anus.  Why is this shocking?  Because: priapulids share all the major DNA and anatomical characteristics with those of Protostomes!  In fact, they are nested among the members of the Ecdysozoa, the exoskeleton-bearing animals that include insects, nematodes, and crustaceans.  All of those animals have protostomic development … why would priapulids be any different in this regard?

Martin-Duran and colleagues (2012) suggest that we have it wrong when it comes to these evolutionary divisions of animals.  It turns out that we may be too hung up on what the blastopore forms.  Instead, Martin-Duran et al. (2012) suggest that it is the separation of the mouth from the anus that is the major adaptation to focus on in Bilaterian animals.  Given that a number of Protostome animals are similar to priapulids in having all the protostome characteristics except that their blastopore forms the anus, it seems that the Deuterostome condition was the most primitive.  In other words, the Protostome condition is derived, and probably developed independently several times.

http://www.sciencedirect.com/cache/MiamiImageURL/1-s2.0-S0960982212011396-fx1_lrg.jpg/0?wchp=dGLbVlt-zSkzV

Figure 4 from Martin-Duran et al. (2012) showing their evolutionary hypothesis for Bilaterian animal development.

What does all this mean?  It means that we now need to re-explore animal relationships and the fossil record to re-test whether the way we understand the evolution of the major animal groups is in need of re-tooling.  Who would have thought that a penis worm and the origin of its anus would have such an evolutionary significance?

References

  • Freeman, S. 2011. Biological Science, 4th Edition. Pearson.
  • Martin-Duran, J.M., Janssen, R., Wennberg, S., Budd, G.E., and Henjol, A. 2012. Deuterostomic development in the Protostome Priapulus caudatus. Current Biology, http://dx.doi.org/10.1016/j.cub.2012.09.037