Bracketing the Past

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.)

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Real Mammals Have TSARS

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