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.
How do we learn about extinct things? Can we use evolutionary theory itself to help us? Yes, but first we need to take a heuristic detour into space.
Suppose you’re an alien from another star system, maybe a thousand light-years from ours. Your scientists pick up radio wave transmissions from Earth, but they are garbled. You know there’s a civilization here, and you can figure that the transmissions came from the third planet, but you don’t have much more detail yet. So, you pack up your spaceship and head over our way.
Unfortunately, in the intervening time, us silly humans manage to blow up the Earth. When you arrive in the Sol system and come out of cryosleep, all that’s left here is a shiny new ring of asteroids where our big blue marble used to be. (Sigh …it happens.)
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 →
Evolutionary biologists are like puzzle-solvers. That’s true for any of the sciences, of course, but there’s one kind of puzzle that evolutionary biologists particularly like to solve: the order of assembly puzzle. Here’s how this puzzle works. Take a complex system that works very well. Now, break it down into its component parts and figure out how they work together (sometimes, this step is done by the physiologist in the next lab over). Finally, figure out the order in which the parts were originally assembled. But there’s a catch: every time you add a part, the system has to form a working whole. It doesn’t have to have the same function as the finished system, but it does have to be a working system. You can’t break an old system until you have a new system in place. Continue reading →