Shared Features in Nature

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The animal kingdom is full of a wide variety of creatures, such as cats, dogs, and mice. Without even thinking, we can probably easily list some of the major differences and similarities between these different species. Dogs bark, cats meow, and mice squeak, for example, making each one unique and different from the others. They each have 4 legs, a tail, and live on land, showing that they also have many things in common.

In fact, if we look at how all life is classified biologically, we see that we can use those differences and similarities to describe exactly how all species are related to one another:

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In biology, all life is divided into a number of groups, with species in each group sharing a number of traits. For example, all animals are in the kingdom animalia, whereas all plants are in the kingbom plantae. So, we know that every animal species shares some characteristics with all other animals, and also some that are different from all plant species.

Then, each kingdom can be divided into a number of phyla, such as chordata, for all animals who share a similar spinal chord structure during some point in their life cycle. Other animals might be in the anthropoda phylum, showing that they share a segmented body and exoskeleton.

We can repeat the process all the way down to the individual species level, uniquely describing each species and the similarities and differences between it and any other species of life we’ve discovered. For example, the common domesticated dog is classified as:

Animalia > Chordata > Mammalia > Carnivora > Canidae > Canis > C. Lupus > C. l. Familiaris

where as the common house cat is classified as:

Animalia > Chordata > Mammalia > Carnivora > Feliformia > Felidae > Felinae > Felis > F. catus

Based on those classifications alone, we know that each species shares common traits through the order carnivora, but they differ beyond that.

Put another way, we can say that both cats and dogs have inherited certain traits from the order carnivora, as well as other classifications they share in common.

This concept of inheritance is the other key concept behind object-oriented programming. In this chapter, we’ll explore how we can use inheritance to show the common elements shared between classes that represent similar items, and how that makes our programs much more powerful when it comes to storing and using those objects.