As my first article in this series pointed out, it is of imperative importance that we include fundamental concepts regarding evolution in our science curriculum for all ages. Not only is it a basic benchmark of science literacy, it is the explanation and answer to biological diversity.
In my teaching experiences, I have found that the word “evolution” provokes either a bored sigh or an excited anticipation among my students. To some, it is a daunting concept that is far beyond comprehension. That’s why I have always avoided using the overarching theme, or title, of “evolution” for a unit. Rather, I embed the concepts within nearly all other science lesson I teach – whether its plant respiration or animal reproduction. Evolution can almost always be an underlying thread in the message of the lesson.
One easy lesson plan that can be adapted for nearly any age is on comparative anatomy. Examining and comparing familiar body structures of animals can provide a clear and easy-to-understand evolutionary message. Such “homologous” structures, or structures that are shared or similar in two species because of common ancestry, are easy to spot. One easy comparison is the forelimbs of some common vertebrates. Hold up pictures of the forelimbs of humans, birds, porpoises, and elephants. Ask your students what they observe about the structures. How are they shaped? What are they used for? Such structures not only share similar form, function and embryological origin, they also indicate common ancestry. Another good way to explain homologous structures is that they help scientists trace a path from one species to another. In other words, the structures are “inherited” among related species.
In contrast, other structures are analogous, which means that although they serve the same function in two or more different species, they evolved independently. In other words, the structures do not share the same embryological material or come from the same structures in a common ancestor. To show this to your students display pictures of the wings on butterflies, birds and bats. These three organisms do not share a common ancestor or even similar habitats or lifestyles for the most part. This displays a fascinating achievement of evolution in that unrelated species were able to develop divergent structures in order to succeed in their own respective environments.
