Here is a credible idea: “We should not eat things that we are maladapted to eat.” On the face of it, this makes perfect sense: if we are maladapted to eating something (or doing anything, for that matter), then clearly it will do us harm. That’s true pretty much by definition. Let’s call this argument the adaptational health argument.
Now, let’s shift the emphasis. The meaning of the statement is actually the same, but when restated, it reveals a problem: “We should only eat things that we are adapted to eat.”
Ah. Now, the shoe is on the other foot! What exactly are we adapted to eat? We have to eat something. How do we choose? What if we have been eating things that we are not adapted to eat?
Since Aristotle, students of nature have been tempted to rank some organisms as somehow “better” than others. Aristotle ranked all organisms from most simple to most complex. In Medieval Europe, his ideas were taken up and incorporated into a grand scala naturae or ladder of life, with lowly worms at the bottom, humans at the top of the mortal beings, and angels above us.
Evolutionary theory has had its share of attempts to understand the scala naturae, usually with time playing the role of the force that makes some organisms more “evolved” than others. Lamarck posited multiple origins of life over the ages and suggested that the lowliest species are newcomers on the world’s stage, whereas loftier species had been around for longer and attained greater heights. Hints of this view still resonate in popular misconceptions about evolution.
What makes a mammal a mammal? In grade school, we were taught that all mammals have three distinguishing characteristics: fur, milk and live birth. But there is a problem: not all mammals have all three of these features. Monotremes (the group that includes the platypus and the spiny echidna) have fur and milk, but they do not give birth to live young. They lay eggs!
So, there seems to be a sort of gray area between mammals and non-mammals. Is there something wrong with our definition of mammals, or do we have a deeper problem? Perhaps there are other gray areas that we need to worry about. Continue reading →
When I’m teaching, I frequently find myself caught between a fascinating digression and the need to keep things simple. For example, if I’m teaching my Human Anatomy class about the lower jaw, I always have to fight an urge to launch into the complexities of lower jaw evolution.
“See? This is the mandible,” I say, “and it’s just one piece of bone.” But all the while, I am clamping my teeth down firmly on my tongue because the exciting truth is that the human mandible isn’t just one bone: it’s really composed of two symmetrical bones, which are called the “dentaries”and are fused together at the midline, but most other mammals have unfused dentaries, and in fact all other vertebrate classes (and the ancestors of all mammals!) have a mandible that is composed of several bones, which include the dentary, the angular, the surrangular and…
You see how it is? The paired dentary thing might be a bit interesting to my pre-nursing students, because human fetuses have that condition. But they could care less about the number of bones in the mouth of a carp and which of those elements are retained by toads and snakes.