Hey now – this makes twenty-two posts! Logistics and season suggest that it would be a great time for a little break, so this post is the final one for … I guess we’ll call it the “first term.” Regular posting, “second term” will resume January 4, 2016. Stay tuned here in the interim though, because some announcements are coming.
As of this writing, my boy-girl twins are eight, and their little brother is nearing seven, so it was extra special for us that Grandmother Fish came along. I’m an evolutionary biologist, and my wife is a veterinary specialist, so they’re already inundated with all things physiological and zoological … but obviously you want to have some good books involved too.
However, when it comes to science, kids’ books look like C. P. Snow was and still is the managing editor. It’s all nature’s pageantry and captains of industry. You can find a zillion dinosaur books, lots of pretty and romantic animal-ecology books, lots of zap-pow experiment books, and plenty that explain the planets or combustion engines or urban planning or farming … but guess what’s left out? You got it. Kids’ books about evolution are close to nonexistent, particularly when humans are involved in a major way, and especially for very little kids who are just beginning to read. Mine are in the older zone for Grandmother Fish; it’s especially good for pre-schoolers.
Grandmother Fish also so happens to be written by a friend of mine, Jonathan Tweet, whom I know from a completely different context, that of (shhh!) pop culture and role-playing games. He and illustrator Karen Lewis have busted out something better than any biologist has yet done. I don’t gush much. This book deserves it. You can see the link to it as a permanent sidebar although as of this writing it’s in-between first and second editions. [copies may be available here]
Here’s the insight which might surprise you: it’s not actually about natural selection. Now, I love me some selection as much as any biologist, but I agree that in introducing evolution, the mechanism of change is simply not the right topic to start with – the point is the genuinely important concept, the one thing that anyone needs to learn: descent with modification results in any given creature being a mosaic composed of retained older features (symplesiomorphies) along with the modified ones (synapomorphies).
The book takes you through through bony fish, tetrapods, amniotes, mammals, primates, and humans, each retaining features of the previous and tweaking some or all of them.
- Grandmother Fish could wiggle, chomp, and swim fast.
- Grandmother Reptile could wiggle, chomp, swim fast, crawl, and breathe air in and out.
- It then proceeds through Grandmother Mammal and Grandmother Ape, adding each time – but also retaining.
Most beautifully, with each change, it also shows the other changes that occurred from the respective Grandmother as well, using term Cousin, so you can see that we could have followed any of the other historical trajectories instead of our own.
And now, my friends, is when we talk more about clades. I learned about this stuff in the harshest of environments, as a graduate student in that crucial generation during which most grad students understood this better than most professors, and I learned how to explain it to them. You can talk about Dollo parsimony and outgroup analysis until you are lovely blue, but no one is going to understand a word until you show that a cladogram is not an “evolutionary tree.” And that also means not diving immediately into the fascinating but arcane realm of making the things, but starting by learning how to read them. [granted we still say “tree” a lot but that is mere tradition]
- Taxonomy: giving creatures names and arranging the names by inclusive names
- Phylogeny: an evolutionary history of which creatures are more and less closely-related to which other creaures
- Dendrogram: a visual depiction of a phylogeny, regardless of methodology
- Systematics: the methodologies for proposing and testing phylogenies
- Also, the idea that you organize your taxonomy to be consistent with a phylogeny
- Cladistics: a systematic methodology (hence, visually, the resulting dendrogram is a “cladogram”)
- Like all systematic methods, riddled with important assumptions and nuances
OK, look at this. Every single V is a clade. In the yellow area at the left, that’s a V within a V, making three groups. That whole clade forms the left side of a bigger V, which is depicted in blue in the middle image, and those two are contained in a big red V which happens to be the whole picture in this case.
That’s not to say that red, blue, and yellow are the only clades – if this were a real phylogeny, they’d probably be just the only ones which have historically been named. If you count, you’ll find FIVE clades (counting nesting) on the left (blue area), and FOUR on the right, making ten in all. Yes, ten! – one more connects the four and the five. So you’d need ten colors … however, as it happens, we don’t actually name every clade. In this case the colors are the named groups, such that the red category is the name for the whole group, and the subcategory would be blue vs. everyone else inside the red, and then, going by the colors anyway, yellow vs. everyone else in the blue.
Therefore the change in the colors – or actually the change on one side or both which is denoted by every V – is only a tiny bit of the creature or creatures in question. Some, in most cases most, of their bodies are still the same old color, or if we drew it with all ten, however many colors were involved so far for their new clade.
Hiya fishy. But do you see how the red is drawn to enclose the blue? And the blue to enclose the yellow? That’s why I just said “inside,” and that’s really important! This is one of the rare diagrams to emphasize that the whole point of the “V” graphic isn’t because it means anything, it’s merely a fast way to draw boxes in boxes to preserve the relationships.
That’s why it isn’t a tree. You never stopped being a primate just because you’re a human. You never stopped being a mammal just because you’re a primate. You never stopped being a vertebrate just because you’re a mammal. OK, you say, I knew that, so what?
Here’s so what: this concept still applies even when the categories, stated outright, violate our cherished notions of ascension.
- Being human doesn’t mean you stopped being an ape.
- Being a tetrapod doesn’t mean you stopped being a lobe-finned fish.
- Being an animal doesn’t mean you stopped being a protist.
- Being a eukaryote doesn’t mean you stopped being a prokaryote.
See, the whole discourse of evolution is tainted with triumphalist rhetoric. We proudly proclaim ourselves mammals insofar as the alternative can be reviled as “reptiles.” We proudly proclaim ourselves tetrapods insofar as it’s tied to a narrative of “conquering the land.” But acknowledging that mammals exist within a non-mammalian clade or that tetrapods are a clade within the one defined by the features of a lobe-finned fish … no, we don’t call that modification of, we call it evolved from, in the false and dismissive sense of away, changed, gone, not any more.
Well that’s just ass and not a pretty mandrill one either. The only things you aren’t are the things that happened in clades that don’t include you. You never knuckle-walked. You never flew. You never photosynthesized. Even the things which you lost along the way – breathing water, true hermaphroditism – are still developmentally and genetically present in certain ways, or at the most extreme, the scars and gaps of their loss are now features of their own.
Now for reading the things properly. First: there’s no critters scattered around inside the diagram, ever. They’re always listed along one edge, and nowhere else. If it’s a critter, then it’s listed in the same row as the rest. The lines are only relationships; they depict nothing. Most especially, they do not distinguish between extinct vs. extant (not extinct) creatures.
Second, there are no axes. Left to right arrangement, or which names are next to which other names, means absolutely nothing. Here, I’ll show you. Let’s take that yellow area on the diagram above and give those three lines names: Abra, Bob, and Cho.
Drawn as boxes, Abra and Bob are contained in their box (clade) and Cho isn’t, but Cho is in the box containing them all, the bigger clade in the yellow area. See how it doesn’t matter whether I arrange A vs. B, or AB vs. C, on the left or right? The box-hierarchy doesn’t change.
You can do that even with the great big eleven-group arrangement, flipping any V or Vs you like left-right. Assign the endpoints A through K and try it. It’ll still stay like this:
Didja see the insight from messing with that? There’s no “big line.” That’s the problem of using the abbreviated Vs instead of the admittedly annoying-to-draw boxes: it’s really easy to get tricked into thinking there is such a line. But you can draw that same big cladogram with any of the taxa positioned at the end of the row, and every single version merely depicts the very same old set of boxes. When you go through every version, it’s easy to see that tracing your finger from the bottom diagonally to the endpoint at the right for any one of them doesn’t mean anything.
Breathe deep now: that’s because in reality, there’s no such thing as a evolutionary trunk or main branch.
No main branch. Whoa. That means … no transitional forms. No missing links. No living fossils. That’s right: all of those terms are blither.
The book to read for this stuff is Robert Martin’s Missing Links, which is dedicated to beating its own title to utter death, and very effectively too. You can bet I’ll be blogging more thoroughly about it.
And you can also bet the way to understand Martin’s book best is to start with Grandmother Fish.
You saw the header – it’s Winter Break! Don’t forget to check back ’cause there are announcements.