Tuesday, February 2, 2016

If birds aren't reptiles, maybe people aren't animals?

Some biological taxa are clades: a clade is a taxon that contains a descendant of every included organism. For instance Mammalia is a clade, while Reptilia is not, since birds aren't reptiles but are descendants of reptiles. There are biologists that wish that we used a phylogenetic classification scheme, one where all taxa are clades. But that's not what is traditionally done. Let's consider the hypothesis that the traditional approach is right in the sense that it cuts nature at joints. Then a taxon can change from being a clade to being a non-clade. I assume that Reptilia changed in this way when birds evolved. And whether such a change has occurred is a substantive question.

In principle, then, it is possible for the kingdom Animalia, which I understand is normally taken to be a clade, to change into a non-clade. And it is a substantive question, then, whether such a change occurred when humans evolved. It could be the case that sapience marks such a departure that we are a new kingdom, and Animalia is no longer a clade. I think a close relative of this thought--albeit without evolutionary connections--is behind the ordinary person's (as opposed to a philosopher's) resistance to the idea that we are animals: personhood is such a transformative feature that it marks a completely new kind of organism.

But while the question is substantive, it's not tenable to say we aren't animals. If we are not animals, it seems we aren't mammals. (Maybe more can be said, though?) But if we aren't mammals, then various natural kind-based explanations fail: we can't say, for instance, that we have complex bones in the inner ear because we have mammals.

Note, too, that the question raised in this post is orthogonal to the question that animalists are concerned with. For all that we animalists need for our positive theory is that we are organisms--whether the particular kind of organism we are is an animal, a plant, a fungus or something else is not very important for the theory.


William said...

The problem of paraphyly in classifying by clade happens every time a subspecies separates from another without extinction of the original species. If dogs came from wolves, are dogs wolves? If we say no, then we are agreeing with those who say birds are not reptiles.

Making humans a different clade from animalia would need biological justification though. In general, adding a unique characteristic to a clade, like complex verbal language in humans, may tend to constitute a new species, but not a new family level clade. To justify paraphyly of a new metazoa level clade one often needs to show the new clade drops defining characteristics of the old clade as well as adding new ones-- birds lack teeth, for example. I wonder if there is anything uniquely human that is a total lack of what other animals have?

Alexander R Pruss said...

I like the idea that loss would be needed.

There might be normative features that other animals have which we lack. For instance, arguably, the primary telos is to reproduce. But our primary tele are to love and know, with reproduction being subordinate to these. However (a) such teleological features are not biological in the modern sense of "biological" and (b) it's still the case that reproduction is among our tele, just that it isn't the highest one any longer.

Here's another possibility. Humans rely on learned behaviors as opposed to instinct a lot more than other animals. Could one perhaps argue that all other animals are capable of basic survival on the basis of merely instinctive behavior, while humans have lost that ability? (But to be honest, I don't know if all other animals are capable of basic survival on the basis of instinctive behavior.)

Dagmara Lizlovs said...

Problem with this set-up is this birds are animals and reptiles are animals. Just because birds aren't reptiles doesn't mean that they aren't animals. It would be more correct to say that people are not fish and fish are not people. Now here is the biology:

1. Humans are mammals. Here's why:


2. Humans are primates, as opposed to felines, canines or equines, although cat, dog and horse owners disagree on that one. Here's why:


Primates also use tools. Among chimpanzees, the females are better tool users than the males. Sorry Tim Allen.


Time for me to go get another banana right now. :-)