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.
During the Industrial Revolution, naturalists in England noticed that the incidence of normal, light-colored peppered moths (Biston betulari) had become scarce in the vicinity of various urban centers. Instead, they were finding a melanistic (dark colored) variety. At the same, time, pollution had caused the local trees to get darker. In 1896, J.W. Tutt proposed that this change was an example of natural selection. The light moths lost their camouflage effect when they sat on the new dark trees, so they got eaten by the local birds. Hence, the moths with the gene for melanism fared better and became prevalent.
The issue was hotly debated and thoroughly investigated through the first half of the twentieth century, and has since become one of the best known and best supported examples of natural selection. You probably remember it from your high school biology class.
Well, the time has come to talk about dinosaurs. In a blog about evolution, it was inevitable. Dinosaurs are, so to speak, the elephant in the room.
It is widely believed that dinosaurs are big and go “Rawr!’. While it is certainly true that dinosaurs go “Rawr!” (of course, there’s a Santa Claus, boys and girls!), it happens that many were not very large.
Some were, of course, brain-meltingly huge. But others were the size of a chicken. In fact dinosaurs came in such a diversity of sizes and shapes, that talking about dinosaurs is a bit like talking about mammals: there are just too many of them to be able to generalize much. Mammals can be giant like an elephant – or a whale – or they can be tiny like a shrew. And they’ve changed dramatically over evolutionary time. Same thing with dinos: the first dinosaurs were quite different from the ones that got smacked down by that asteroid at the end of their reign.
But there’s one thing that seems to have remained the same over the entire age of the dinosaurs: the carnivorous ones always had a bipedal stance. From Allosaurus to Velociraptor, they all seem to have run on two beautifully engineered legs. Herbivores came in a surprising array of shapes both two-legged and four; but carnivores? Just the two-legged variety.
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.