Once you have introduced the topic of evolution, you will want to move on to its primary component – natural selection and how that process works.
Usually at this time I will also introduce Lamarke’s Theory of Acquired Characteristics, but you have to be careful with that. If its the first thing you talk about, you might accidentally make it the only thing they remember, and since Lamarke’s theory is an example of a theory that did NOT work and was discarded in favor of Darwin’s theory, it is preferable that students don’t get “stuck” on it.
Starting off with natural selection is easy if you give students organisms that do are simple. I actually make up my first set to show as an example. There are four points to natural selection – Variation, Competition, Survival, Reproduction.
Write those on your board or on a poster somewhere and leave them up in your room for the duration of the unit. Be prepared to return to those four points frequently.
Here’s the example I start with
1. Variation – this species of Blob comes in a variety of colors, and some have sharp pointy noses and others do not. Blobs eat food that lives on the ground and underground.
2. Competition – during a dry year, food became scarce. Blobs that could probe underground for food had an advantage.
3. Survival – blobs that could not find food, died. Most of the ones that died did not have the long noses.
4. Reproduction – the long nosed blobs reproduced.
Over time, blobs all had the long noses which helped them to dig for food.
And that is NATURAL SELECTION – blobs with advantageous traits (adaptations) passed those traits to their offspring.
Expand on this with real organisms. Ask students to imagine how this same process would work in giraffes so that over time, giraffes would have longer necks.
Modeling Natural Selection
I also have students model natural selection using a NeoSci Kit which has them place peppered moth models on different colored backgrounds. Students take turns grabbing the moths and recording how many of each color were eaten – see Peppered Moth Simulation Kit. You can also do a version of this lesson where you use newspapers as a background, though it will require some set-up – See Peppered Moth Simulation.
Modeling Natural Selection on the Computer
Online simulators can work very well to model natural selection also. I have several that I have used with freshman and AP students – though a warning, some are more advanced than others and you should plan on trying them yourself before students do them. I love the biologyinmotion simulator, but younger students have a hard time with the controls.