More Evidence for Evolution

Scientists often apply uniformitarian arguments.
(Huh?)
Uniformitarian arguments are arguments based upon the idea that processes operating today were operating in the past too. If we extrapolate those processes back in time we can account for current observations.

These types of arguments are common throughout science and perhaps an example from outside Biology might help.
For centuries geologists have known that the flow of water in a river cuts away at its banks producing a deeper and wider channel. Eventually, the walls of the channel give way and produce a wider basin in which the river runs. Given enough time a river can cut a deep canyon through the rock and produce spectacular results - like the Grand Canyon! Geologists use uniformitarian arguments to explain that the Grand Canyon was formed by the same processes at work today, but continued over many years.

The evidence for evolution, that you learned about earlier, can be used as the basis for an uniformitarian argument for all of evolution. The evidence you have seen so far shows examples of small changes in populations and, given enough time, they could give rise to a wide diversity of organisms. (In much the same way that a small river can give rise to a wide valley - given enough time.)

However, we don't need to rely on uniformitarian arguments.
In this lesson we will consider how we can infer evolution from other kinds of evidence - the similarities between living organisms and the fossils left behind. As you will see, both of these lines of information provide historical evidence for evolution.

First let's consider similarities. You may be surprised to know that there are two ways for things to be similar. Similarities can be analogous or homologous.

Analogous similarities are those caused by convergence due to similar environments or strategies. For example, all rockets look pretty much the same. They are all tall and thin with powerful thrusters at the rear (bottom). This similarity in the shape of rockets is an analogous similarity. All rocket designers face the same problems. How do you get a rocket off the ground and send it as fast as possible through the air? The physics and engineering problems are the same so the solutions are pretty similar. Independent rocket designers came up with analogous designs for their rockets.

Nature comes up with analogous designs in the form of converging evolution.

Dolphins and most fish have analogous similarities in their design (shape).
What was the selection force that drove the converging evolution of dolphins and fish?