Phylogenetics is Moon Man Talk

Phylogenetics is the study of the evolutionary history and relationships among extant and extinct organisms. More than any other organizational scheme, this is the way biologists think about the living world. In vertebrate paleontology in particular, an understanding of the evolutionary relationships of animals as identified via minute anatomical details is absolutely fundamental to our science. One might even argue that most new discoveries and inferences in this field are meaningless without some knowledge of the basic shape of the tree of life.

I’ve spent about eight years so far teaching science in museums, parks, and classrooms. And based on my anecdotal experience, most discussion of phylogeny comes across as incomprehensible babble to a plurality of people. For instance, one of the most commonly used definitions of “dinosaur” among paleontologists is “the most recent common ancestor of Triceratops and modern birds, and all it’s descendants” (there’s also the similar “most recent common ancestor of Megalosaurus and Iguanodon, and all it’s descendants”). This definition is not meaningful to most people. As evidence, I submit the following set of questions, all of which I have been asked by intelligent and well-meaning adults:

  • Did whales and dolphins evolve from marine reptiles?
  • Did giraffes evolve from sauropods?
  • Are [dromaeosaurs] related to cats?
  • Are dinosaurs related to sharks?
  • How can birds be dinosaurs if dinosaurs are reptiles?
  • Did the plant-eating dinosaurs evolve into mammals?
  • Are bats a kind of bird?
  • Are pterodactyls a kind of bird?

I don’t mean to ridicule or disparage people for asking these questions. Again, these all come from educated adults – museum and park visitors, undergraduate students, T.A.s, and at least one veterinarian! While these questions clearly show unfamiliarity with evolutionary relationships and how evolution works in general, they also show an effort to build a logical framework when none is available. For example, when a person asks if whales are descended from marine reptiles, he or she is hypothesizing that all large marine animals are related. This is incorrect, but it’s a sensible connection to make (and one that past naturalists have certainly explored).

For science communicators, this deficit of phylogenetic understanding is a serious problem which continuously undermines attempts to interpret zoology and paleontology. For example, think about how little meaning a statement like “Dimetrodon isn’t a dinosaur” has to somebody who can’t articulate what a mammal is or what a dinosaur is, much less the evolutionary distance between both groups. This is what we should expect from most of our audience, which means there is always a lot of catch-up work to do when explaining something as simple as the basic identity of a given organism. By the time you’ve satisfactorily defined “dinosaur” (good luck with that), explained the synapsid-diapsid split, discussed the tree of extinct stem-mammals, and positioned each of these things in deep time, you’re five minutes deep into a lecture when all you were asked was “what is it?”

USNM 8635, a handsome non-dinosaur. Photo by the author.

USNM 8635, a handsome non-dinosaur. Photo by the author.

How can we solve this conundrum? The first step is to divide the issue into a number of smaller problems:

  • People don’t understand the fundamentals of how evolution works
  • People are unfamiliar with basic vertebrate classification
  • People lack knowledge of key evolutionary events through deep time
  • People don’t understand what traits are significant when assessing evolutionary relationships

The first problem is well known and has been discussed in-depth elsewhere (e.g. MacFadden et al. 2007, Spiegel et al. 2006, Spiegel et al. 2012), so I’m going to breeze over it and focus on the other three.

Basic Vertebrate Classification

It’s easy to toss out words like “mammal”, “reptile”, and “amphibian”, and take for granted that your audience will know what they mean. But even the most basic elements of vertebrate classification are specialized knowledge, and science communicators would do well to remember it. When I was teaching an undergraduate human anatomy course, I found that most of the class was familiar with the word “mammal”, and could name some examples. However, the students couldn’t articulate what sets mammals apart from other animals, and the relationship of mammals to other vertebrates within the tree of life was all new to them.

I think this is fairly typical, even among individuals with a background in biology. People are introduced to these categories in grade school, and you’d be hard-pressed to find somebody who couldn’t tell you whether (say) a cat is a mammal or a reptile. What is missing is what that actually means. We can’t assume that just because somebody knows a cat is a mammal, they know that fur and milk glands (much less auditory ossicles, a solid mandible, and heteromorphic teeth) are things to look for when categorizing mammals. They also may not know that “mammal” is an evolutionary group – that all the animals that fall under this banner are more closely related to each other than they are to anything else. No mammal is going to spontaneously become a bird or a fish. This is obvious to specialists, but not to most of our audience.

Evolutionary History Through Deep Time

The situation is further complicated by the element of time. Somebody may know that a modern cat and lizard differ in several fundamental ways, but do they know that both groups still evolved from a common ancestor? Or that said ancestor lived more than 300 million years ago? Unfortunately, much of the public would appear to lack any knowledge of how the past is related to the present. I’ve had visitors insist on calling fossil turtles “dinosaur turtles” and Teleoceras a “rhino-saur.” For them, extinct animals (all labeled “dinosaurs”) are a category all their own, wholly independent from the categories that describe modern animals.

For specialists, it’s obvious that modern animals exist within a continuum that extends into the deep past. It’s also obvious that groups like “mammals” and “reptiles” had starting points, and are embedded within larger, more ancient groups. None of this can be considered common knowledge, but it’s critical to any discussion about the identity or categorization of a given taxon.

better than a tree

Box diagrams are a simple and intuitive way to ground students’ understanding of the diversity of life.

How can educators hope to cover so much ground without confusing, distracting, or alienating their audiences? One option is to use a cladogram, or evolutionary tree. Trees are absolutely the most precise and accurate way to portray relationships over time, but as Torrens and Barahona demonstrate, they are regularly misinterpreted by the public. When I’m dealing with a general audience, I prefer box diagrams like the one above. Boxes within boxes show tiers of relatedness in a way that is more intuitive and easily understood than a tree. Box diagrams allow educators to cover a lot of unfamiliar ground quickly, and it’s easy to test visitors’ comprehension by asking them to point to where an example taxon should be placed. While this visualization of vertebrate relationships lacks a time axis, people can at least grasp the relative order in which each group evolved (fish before amphibians, amphibians before reptiles and mammals, etc).

How Scientists Discover Evolutionary Relationships

Going back to the list of misguided questions at the top of this post, we can generally surmise the thought process that led to each inquiry. The person who asked if whales and marine reptiles are related was classifying based on shared habitat. The person who asked if giraffes evolved from sauropods was classifying based on similar body shape. We can also see classifications based on diet, and based on shared activities, like flight or attacking prey with clawed feet. All these questions reflect a misunderstanding of what kinds of traits researchers look for when working out evolutionary relationships. So how do we quickly and clearly explain which traits are relevant, and which ones are not?

This is a tricky problem, and one I have not found a perfect solution to. The most important distinction is between plesiomorphic and apomorphic traits: plesiomorphic traits are inherited from an ancestral form, while apomorphic traits are novel developments. Put simply, working out a phylogenetic tree is all about grouping organisms based on shared apomorphies. The more apomorphic traits between two species, the more closely related they are. Once introduced, this is a fairly intuitive distinction. You don’t even need to use the jargon – “old traits” and “new traits” will often suffice. Going back to our  problem of defining Dimetrodon, we can clarify that the lizardy shape and general toothiness are “old traits” – so they don’t tell us much about what the animal actually is. Instead, scientists look at “new traits”, like the number of postorbital fenestrae, to work out Dimetrodon‘s evolutionary affinities.

All of this is a long-winded way of saying that relating phylogeny to the public is challenging, but very important. Too often, science educators assume visitors have more background than they do, and the discussion comes across as so much moon man talk. Alternatively, educators push past complicated parts too quickly, which leads to confusion or misunderstanding. Ultimately, being a good educator comes down to two things: knowing your content and knowing your audience. Both are equally important, and both need to be practiced and refined in equal measure to ensure successful communication.

References

Macfadden, B.J., Dunckel, B.A., Ellis, S., Dierking, L.D., Abraham-Silver, L., Kisiel, J., and Koke, J. 2007. BioScience 57:10:875-882.

Spiegal, A.N., Evans, E.M., Gram, W., and Diamond, J. 2006. Museums and Social Issues 1:1:69-86.

Spiegel, A.N., Evans, E.M., Frazier, B., Hazel, A., Tare, M., Gram, W., and Diamond, J. 2012. Changing Museum Visitors’ Conceptions of Evolution. Evolution: Education and Outreach 5:1:43-61.

Torrens, E. and Barahona, A. 2012. Why are Some Evolutionary Trees in Natural History Museums Prone to Being Misinterpreted?” Evolution: Education and Outreach 1-25.

13 Comments

Filed under education, opinion, science communication, systematics

13 responses to “Phylogenetics is Moon Man Talk

  1. Andrew Stuck

    I feel like this post ties in nicely with a recent post by Mark Witton on the seeming over-exposure of dinosaurs in paleontological outreach.

  2. Ben

    Yep – Mark’s post is fantastic and has given me lots to think about. I think the most relevant bit is when he mentions the general confusion about what a dinosaur actually is – perhaps the overwhelming dominance of dinosaurs is in part driven by the fact that when people demand to see dinosaurs, they really mean prehistoric animals (and then educators take them at their literal word).

  3. jerrold12

    At AMNH, I often like to ask first “who is more closely related to you, your sister or your first cousin?” With most recent common ancestor introduced, the next query is “Who is your closer cousin, T. rex or an octopus?” This brings in mouth as ancestral and backbone as derived.

    • Ben

      Good tip, thanks! Is that in a “tour” context, a “station context, or something else?

      • jerrold12

        Both! I work in three roles: Teaching Volunteer (school groups and regular visitors), Tour Guide (highlight and spotlight tours) and Fossil Explainer (wandering the 4th floor fossil halls). I may follow up by noting that the visitor already knows evolution and natural selection. She knows that every organism reproduces, that not all of the offspring are identical and that not all survive to have offspring of their own. Reproduction, variation, selection; voila! evolution. (Courtesy of Prof. Cameron Smith). Then I tell her (if young) that all else is detail and she now has a career open in biology, agriculture, medicine or whatever she wants. (Dobzhansky quote).

  4. 1stly, sorry for not keeping up with/commenting on your blog like I should. 😦

    2ndly, I’ve meaning to tell you how much I like the “Framing Fossil Exhibits” series in general & the AMNH/FMNH posts in particular. I like them so much that I quoted them in “The worst alternative” ( https://www.amazon.com/review/R1Y51RJP1YORCC/ref=cm_cr_dp_title?ie=UTF8&ASIN=1416938575&channel=detail-glance&nodeID=283155&store=books ) & will quote them in future reviews. Here’s hoping you like “The worst alternative” (&, assuming you have an Amazon account, vote Yes for it 😉 ).

    3rdly, many thanks for this post. I hope you don’t mind, but I have a lot to say about it.

    “People are introduced to these categories in grade school, and you’d be hard-pressed to find somebody who couldn’t tell you whether (say) a cat is a mammal or a reptile. What is missing is what that actually means. We can’t assume that just because somebody knows a cat is a mammal, they know that fur and milk glands…are things to look for when categorizing mammals. They also may not know that “mammal” is an evolutionary group – that all the animals that fall under this banner are more closely related to each other than they are to anything else.”

    If that’s the case, then I’m surprised, given that even I (I.e. A stupid idiot who grew up in various small hick towns) knew & heard all that in grade school: That some animals are more closely related than others; That the more closely related ones share certain features that others lack (E.g. In reference to mammals, even whales have some body hair). My life-long interest in dinos & educational tv might’ve helped, but I still didn’t know much else about evolution until college. Speaking of educational tv, the “Who’s Who?” episode of “Kratts’ Creatures” may be the best children’s tv explanation of how animals evolved (& thus, should be required viewing for anyone who talks to laypeople about phylogeny).

    “as Torrens and Barahona demonstrate, [cladograms] are regularly misinterpreted by the public.”

    Cladograms on their own, yes, but if an educator is using one like you describe (“How can educators hope to cover so much ground without confusing, distracting, or alienating their audiences? One option is to use a cladogram, or evolutionary tree”), then that shouldn’t be a problem b/c the educator is there to clarify the cladogram like I did.

    “Basic Vertebrate Classification…Evolutionary History Through Deep Time”

    You’re obviously much more intelligent/experienced than I could ever hope to be. However, I feel like maybe I can provide a different perspective (& thus, a possible solution), given my personal experience as a stupid idiot who had to figure out a lot of that on his own through trial & error.

    When laypeople ask me what something is, I 1st ask them if they know what reptiles/mammals/etc are & then describe the something accordingly. For instance, when talking about dinos, I describe reptiles as “4-legged backboned animals characterized by keratin scales (among other things)”, dinos as “land-living reptiles with an erect posture”, birds as “flying (or secondarily flightless) feathered dinos”, etc. In your case, I’d describe mammals as “4-legged backboned animals characterized by body hair & milk glands (among other things)” & non-mammal synapsids as “proto-mammals, or extinct relatives of true mammals”.* Also, when asked why something (E.g. Pterosaurs) isn’t part of a certain group (E.g. Dinos), I say, “All dinos (including birds) share a common ancestor & certain features inherited from that ancestor (E.g. An open hip socket). Pterosaurs lack said features, which is how we know they’re not dinos.” If/when need be, I explain that said features might seem small/insignificant to us, but make a big difference in the evolution of said animals (E.g. An open hip socket allowed the erect posture of dinos, which allowed them to run faster & grow larger than other reptiles). Does that help?

    *Seriously, educators should use “proto-” more often. It helps a lot when describing intermediate groups to laypeople (E.g. Non-dino dinosauromorphs = proto-dinos, or extinct relatives of true dinos; Pseudosuchians = proto-crocs, or extinct relatives of true crocs; etc).

    “How Scientists Discover Evolutionary Relationships”

    Have you read Hedley’s “Dinosaurs and Their Living Relatives”? If not, I definitely recommend doing so. It may be the best children’s dino book when it comes to explaining that (& thus, should be required reading for anyone who talks to laypeople about phylogeny). I like it so much that I reviewed it in “Cladistics yay!” ( https://www.amazon.com/review/R1SCM65CLPZD4M/ref=pe_1098610_137716200_cm_rv_eml_rv0_rv ). Here’s hoping you like “Cladistics yay!” (&, assuming you have an Amazon account, vote Yes for it 😉 ).

  5. EDIT: I meant to say “the educator is there to clarify the cladogram like I did as an educator” & “Non-croc pseudosuchians = proto-crocs”.

  6. Ben

    Thanks for the in-depth comment, Herman! You need to stop calling yourself an idiot – it’s clearly not true, and you’ve clearly given these issues a lot of thought! Very good suggestion on the use of “proto” – I think you’re right that it’s a widely understood term, and when trying to convey concepts quick every word counts. I might start borrowing that…

    • 1stly, many thanks for getting back to me. Also, many thanks for the kind words. I am kind of an idiot (especially compared to you), but I get what you’re saying. I shouldn’t be so negative.

      2ndly, if/when you’re not too busy, I was wondering what you think of my book review reference to you (Does it do you justice?), my Hedley book recommendation (Have you read the book? If so, what do you think?), the cladogram paragraph (Is it helpful?), & the “When laypeople ask me what something is” paragraph (Besides the “proto-” stuff, is it helpful?). Many thanks in advance.

  7. Hey Ben! You might be interested in an educational art project of mine that involves teaching evolution through art by having people simulate evolution by copying each others drawings generation after generation. When we’re finished I have a literal paper trail of evolution, and later I arrange all of the drawings into massive phylogenetic tree images.

    You can see some examples and more about the project here https://evolutionanimation.wordpress.com/what-is-this/

    I’m usually teaching kids when I do this, but I’ve done adults to, and it’s interesting seeing peoples brains get stuck on the same issues over and over again. I’m not 100% sure if they fully understand what I’m talking about, but they definitely see things as ‘winning and losing’, ‘humans/technology as apex’, etc. In relation to real-life plants and animals I tend to stress that they’re all alive at this moment because all of their mothers and fathers and grandparents etc. had survived through all of history to this point, and that goes for everything else that’s alive at this point in time, and so that if you go back far enough, we all share the same distant grandparents. Even the youngest kids understand that things like dinosaurs are extinct, and everyone seems to get a kick out of the idea that people are descended from fishy ancestors.

    Once I show everyone our huge twisting crayon drawing phylo trees at the end I think it does help their understanding, because while I do have a common ancestor there’s no ‘central trunk’ to my ‘trees’ and they just fly off in all directions. I’ve wanted to try an activity to make the cladogram in reverse , in that I know the exact ‘natural history’ of this fake world because I have a paper record, but if I hand them a bunch of drawings, can they place them correctly in a tree on their own just by looking at them? I think the abstraction of the ‘invented’ animals might help in that regard, so people wouldn’t get caught up on the “correct” interpretation of whether or not bats are birds. Something I’ll have to try at some point in the future I guess!

    • Ben

      Hi Tyler, thanks for the link – your project rules! Have you found that there’s a particular age cut-off when the students are too young to grasp the game and its implications? I’d love to give this a try…

      • Originally I was doing groups of kids that were roughly in the third grade or so. Then I had a group where they accidentally had 1st graders through 5th graders in the same class, but everything went smoothly. Since those initial groups I’ve kept going younger and younger (and older) and no, there doesn’t seem to be a limit. As long as they can copy a picture to some degree, you can keep the ball rolling.

        As far as how much they understand, I’m not sure, but my main goal was to make something memorable first, so that even if they had no clue what I was doing, they would probably remember it, and when they came across the concepts of evolution later something would stir in their brain. The game continues to ‘work’ even if they’re unaware of what they’re doing in the same way that plants and animals aren’t aware that they’re evolving. Younger kids are probably more interesting in this respect in that their thought process is more ‘naive’ and they have no preconceived notions of what they ‘should’ be doing, or in some cases have no idea what it is I’m asking them to draw.

        This is a good example where I asked kindergartners to draw a trilobite.
        https://evolutionanimation.wordpress.com/2014/11/02/trilobites/
        None of them knew what a trilobite was, and they panicked immediately because my initial drawing was “too hard” (basically a circle with eyes, they were just afraid to draw). I more or less just kept telling them to copy the drawing again and again, adding ‘splits’ in the shell as articulation. You’ll see by the end the drawings suddenly become complex, and more or less look like actual trilobites,. If I had shown them their own drawings at the start they would have insisted they couldn’t have drawn something that difficult.

        On occasion I’ve done drawing chains with flowers and butterflies and had parents let their babies doodle on a sheet on paper. Afterwards the parents seem to be casually dismissive that their kid actually drew anything but scribbles, but you can still make out the parts of a flower or insect, they just lack almost all hand eye coordination so things are very abstracted.

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