Evolution Theory, Evidence & Rates

Instructor: Christie Spadafora

Christie has a B.S. and an M.S. in Biology. She teaches life and chemical science courses at college, high school, and middle school levels in MA.

This lesson will briefly introduce the theory of evolution, discuss a few pieces of evidence supporting the theory of evolution, and discuss the rates of evolution.


What do finches, bug spray, and the soot-filled air of the Industrial Revolution have in common? Well, they, along with many other organisms, chemicals, and occurrences, have helped scientists figure out how populations of organisms change over time.

It has taken several scientists hundreds of years to explain the theory of evolution that states that groups of organisms change over time. In essence, a current population of kangaroos is a product of several changes that have occurred over millions of years, resulting in the kangaroos we currently see.

Maybe you've heard of Charles Darwin? He's perhaps the most famous evolutionary scientist. He published his theory of evolution by natural selection in 1859. Let's see how finches, bug spray, and soot can help us understand this theory, look at evidence that supports it, and see how often it occurs.

Charles Darwin

The Mechanism of Evolution

When Darwin was visiting the Galapagos Islands, he noticed something interesting about the finches living there. It seemed that the finches didn't share the same type of beak, but rather, some finches had tiny, pointy beaks, while others had large, rounded beaks.

Darwin knew a mechanism was behind the change, or evolution, that had occurred, creating different beaks. He called this mechanism natural selection. Darwin proposed that over time, a population of finches could develop different beak shapes in order to best eat whatever food was most available to them, thus allowing them to survive better.

He used the term 'survival of the fittest' as a short hand for organisms so well-suited to their environment that they will live long enough to reproduce, passing their traits, like beak shape or eye color, to the next generation.

Finch beaks evolving with time

A single organism cannot evolve; rather, a population of organisms can evolve. One finch cannot evolve its beak to adapt to currently available food. Rather, finches with well-adapted beaks will eat well and live long enough to reproduce, thus creating more finches with well-adapted beaks.

Similarly, finches with beaks that don't help them crack open nuts or dig for worms won't live long enough to reproduce, thus preventing this type of beak from being passed on to the next generation.

Evidence for Evolution

Much evidence supports the theory of evolution by natural selection. One example involves bug


Human Interference

Humans have often been the instigators of evolution. Farmers use pesticides to kill unwanted insects. If a farmer sprays a pesticide, and it kills 90% of the population of insects, 10% of the insects had a trait that allowed them to survive the chemical bath. When they reproduce, their offspring will also have the trait that allows pesticide-survival.

What happens when the farmer tries to spray the crops again? Well, let's just say the farmer won't be as happy this time around. The new population of insects is different than the original population of insects, and thus, evolution has occurred!

Still wondering how the soot has anything to do with evolution? Prior to the Industrial Revolution, the peppered moth had black and white wings. However, as the Industrial Revolution increased the amount of soot and smog in the environment, a new version of these moths was seen for the first time - solid black. The black moths were able to camouflage themselves against the pollution better than the peppered moths, thus better escaping predators. In just a century, human pollution had caused a population of moths to evolve.

The peppered moth


Fossils are also evidence of evolution. Fossils are preserved pieces of biological history that provide information about organisms that are no longer alive. Scientists trace evolutionary changes by comparing fossils from different time periods.

This comparison works with DNA too. With the help of computers, scientists compare the full DNA sequences of one organism, like a human, to another, like an ape, to see how similar they are. Strong similarities in DNA sequences help scientists to determine which organisms share a common ancestor.

Evolution of horse feet and teeth over time, with the most recent at the top

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