Direct Continuation of: Birds Are Dinosaurs, But Pluto Isn’t a Planet, Part II

So recently I’ve been talking more about definitions — and how some definitions can be better than others based specifically on the criteria of practicality. I did this by staking out two claims that are not only true, but an example of how we use definitions, and how definitions change as we encounter new knowledge: “Some birds are dinosaurs” and “Pluto is not a planet”.

In Part I, I talked about how accepting a change in a definition does not mean that anything has changed in the object that is being described, largely due to differences between the map and the territory and the reason smuggling connotations is a fallacy.

In Part II, I moved on to talk about past times in history when definitions changed, and why they did so — using the cases of polywater, H₂O, and the atom. I talked about what we should do with definitions when we learn new information about the objects we are defining, and how we always seek to make practical distinctions.

I then explained why it is that Pluto is no longer a planet: because it has been joined by a dozen or so other newly discovered stellar bodies (now called dwarf planets) and because Pluto, along with the newly discovered members, was easily distinct from the eight current planets by both size and the “cleared the neighborhood” designation.

Now I will explain why we should accept the statement “some birds are dinosaurs”, and tie in what I’ve been talking about definitions along with another discussion of recent science.

 

 

Breaking Down a Definition

What does it mean to say that “some birds are dinosaurs”?

Here, we might be tempted to go with the fact that, theoretically, it could mean anything — they’re just words, and there is no law outside of language that says we should use this word to mean this thing, since it’s a mostly arbitrary association.

But we can fight that with what I will now call the criterion of reasonable common usage, or the idea that you shouldn’t ditch the commonly accepted and agreed upon definition unless you have a good reason to do so, as in a reason where the benefits of the new usage outweigh the costs of the confusion involved in not using the common term (see Part I and Part II of this series for establishing this).

The criterion of reasonable common usage would suggest that you ought to view the statement “some birds are dinosaurs” as three definitions: the implication of “bird”, the implication of “dinosaur”, and the implication of the “some [X] are [Y]” construction.

I will now further break down these three statements. Yes, this is the kind of fun you get to have when doing philosophy.

 

So what is a bird? A bird is “a feathered, winged, bipedal, endothermic (warm-blooded), egg-laying, vertebrate animal”.

What is a dinosaur? A dinosaur is “defined as the group consisting of ‘Triceratops, Neornithes [modern birds], their most recent common ancestor, and all descendants’”

What does some [X] are [Y] mean? It means that there exist members that fit the definition of [X] that also fit the definition of [Y], that is that there is overlap between the definition of [X] and the definition of [Y]. It’s an example of syllogistic logic.

How do we know some birds are dinosaurs? Because the scientific definition of dinosaurs includes birds as part of the category, making the idea that “birds are dinosaurs” definitionally true.

So by the criterion of reasonable common usage, you must accept that some birds are dinosaurs.

 

 

But Why Count Birds As Dinosaurs?

Though it might not be enough to merely accept the common usage, because it does sound dreadfully arbitrary: why did scientists agree that dinosaurs should include birds? Don’t we just think of towering T-Rexes and stuff?

But this actually represents a recent shift in science that’s happened within the past decade — so much now that scientists use the phrase “non-avian dinosaurs” to refer to what we think of the normal dinosaurs, the large ones that are more obviously reptillian and died out somehow. Specifically, the science shows that birds are the evolutionary descendants of perhaps the Dromaeosauridae or some similar biological family.

Summarizing this article from Berkeley University, the Wikipedia article on the Origin of Birds, and a few other sources, the story goes pretty much like this:

 

While as early as the early 1600s some anatomists were noticing similarities between reptiles and birds that were not present between other types of animals, it wasn’t until Charles Darwin wrote the Origin of Species in 1859 and Christian Erich Hermann von Meyer discovered the Archaeopteryx in 1861 that the pieces started falling in place.

Here we had a fossil of a therapod dinosaur that was capable of flight, and only grew to about half a meter in length, and quite possibly possessed feathers. We also had a theory of biological evolution that would eventually be formulated strong enough to prove that this Archaeopteryx demonstrated evolution from the therapod dinosaurs to the modern birds. Because of this modern birds are considered a therapod dinosaur.

However, there are other broad connections between non-avian dinosaurs and their avian counterparts: specifically, they have highly similar skeletal structure and highly similar respiratory systems. Both groups also lay eggs with a similar microstructure and develop their eggs in a similar manner.

Additionally, both groups have similar brooding behaviors in caring for young as suggested by observations of modern birds and discoveries of dinosaur fossils in certain groups. Lastly, a recent discovery of potential soft tissue from a Tyrannosaurus leg bone discovered in MOntana compared very similarly to that of chickens, suggesting that older theropods and birds could be closely related.

 

 

The Way of Distinction

It’s lastly important to not that it is not correct to say that birds evolved from dinosaurs into something that is not a dinosaur, for the same reason that it is not correct to say that Pluto is a planet: because of the way distinctions are made.

First, recent evidence demonstrates that certain birds such as the Ostrich and Pigeon are more similar to the Tyrannosaurus and Velociraptor than the Tyrannosaurus and Velociraptor are similar to the Stegosaurus.

Additionally, the Ostrich and Pidgeon also are closer in time to the Velociraptor (separated by 71 to 75 million years, Cretaceous Period) than the Velociraptor is to the Stegosaurus (in the Late Jurassic period 150 to 155 million years ago, so 75 to 84 million years before the Velociraptor).

So if we were to consider the Ostrich and Pidgeon a distinct group undeserving of the term dinosaur, we could not then also apply the term dinosaur to both the Velociraptor and the Stegosaurus without being arbitrary and inconsistent.

 

 

Conclusion

So there is a clear difference between a needless semantic quibble and a distinction worth making. One of these is the notion that some birds are dinosaurs. Again, these aren’t birds that once were dinosaurs, or the idea that some dinosaurs were once considered birds at some point, but the fact that some commonly found birds, such as the pigeon, living today, ought to be considered living dinosaurs.

Consider everything we’ve learned: no characteristics about pigeons change whether or not we personally consider them dinosaurs, hell we could call them fnords and they would still have the same biology and behavior. Dinosaurs or not in the map, the similarities between birds and non-avian dinosaurs will remain the same in the territory. If we want our map to reflect this territory, we need to make this change in our definitions.

 

And think again specifically about smuggling connotations — just because we think of the T-Rex as fierce, large, and powerful does not mean that we need to apply these adjectives to pigeons and ostriches.

It is all these things that makes it both a big and not a big deal that we accept the statement that “birds are dinosaurs, but pluto is not a planet”. It’s a big deal because it represents a lot of knowledge that we’ve recently gained in both archaeology and astronomy that we should reflect in the way we practically employ our words to describe the world around us. But it’s not a big deal because nothing will change about the facts of archaeology and astronomy if we deny this statement.

 

So now we know what Pluto and birds have in common: both have had our view of them changed as a result of recent discoveries that were of sufficient magnitude to change the way we describe our world. Because the way we describe our world is a direct result of what we know about the world.

So, recognize that there are many times where debating definitions is not a folly. There is a lot to optimizing the practicality of how we talk, and it sometimes isn’t just semantics.

We just have to strike a careful balance between the Pluto debate and the debate about free will.

Followed up in: The “Why Do We Care?” Test