The profesor speaks about how nature selects specimens. He puts en example of how a plant makes a wooden ball to protect it from a parasite. Then he explains with the example of this plant the types of population that can live in a zone.

This is the original population, with a lot of medium especimens and a few very big and a few very small.

Then he explains what happens when there are much more specimens of normal size and any bigger or smaller, this is stabilizing selection.

He explains that this is directional selection, he sais that this can happen to his example if one year there is a lack of woodpeckers, there would be more bigger specimens.

This is diversifying or disruptive selection and here there are more small and big specimens than normal size specimens.

Finally he speaks about sexual selection, and that are the females the ones who choose the male and the genes that she wants to pass to her offspring .