Themes in Biology: Diversity, Interdependence & Evolution

Instructor: Meredith Mikell
Biology is broadly divided into three key themes: diversity, interdependence, and evolution. We'll describe each of these themes and explain their importance to understanding life as a whole. At the end, you can test your knowledge with a brief quiz.

Complex Life

Life on Earth is simply amazing - diverse, resilient, powerful, intelligent, and mystifying. The more we learn about living things, the more we reveal deeper complexity; each question answered is accompanied by many more questions asked. In the time that humans have studied biology, we have been able to loosely categorize our understanding of it into three major themes:

  • Diversity
  • Interdependence
  • Evolution

Whether we're studying microscopic bacteria, towering redwood trees, or gargantuan whales, these three themes are at the crux of life.

Diversity: We Are Many

The study of (bio)diversity involves accounting for and classifying the many different types of living things on Earth. With the discovery of each distinct species, be it alive now or extinct, our awareness of the vast biodiversity of our planet increases. On the most general level, all life can be divided into three major domains:

  • Bacteria: single-celled microscopic organisms found literally everywhere across the planet, including inside of your own body!
  • Archaea: single-celled, microscopic organisms that are similar to bacteria and generally love extreme environments.
  • Eukarya: more complex single-celled and multi-celled organisms, ranging from a single paramecium to fungi, plants, and animals.

All living things are grouped into three major domains, from which they are further classified.

From this basic classification system, each domain is further classified into kingdoms, then phylum, class, order, family, genus, and species.

A sample of different types of fungi, illustrating their vast biodiversity.

It is important to point out that living things do not always fit neatly into our method of classification. Earth's amazing diversity of life is far more complex than our way of labeling. But classifying biodiversity is a dynamic process itself, and allows us to best understand how each species relates to the others.

Interdependence: We Are Connected

All of this diverse life on Earth would not exist if not for the complex and dynamic interactions between organisms. This is where the concept of interdependence comes into play. Scientists in the field of ecology study the interactions between organisms, especially the ways in which they depend on each other. For example, we depend on oxygen to breathe. Oxygen is the byproduct of plants and algae undergoing photosynthesis. When we exhale carbon dioxide, these plants use it to make oxygen and basic sugars. Humans, as well as many other organisms, eat plants to get that energy. This is just one basic example of interdependence among living things. Other examples include:

  • Predator-prey relationships
  • Symbiosis, a co-dependent relationship between two species that can be positive or negative for one or both species.
  • Territoriality
  • Competition for resources.

Coral and anemones have a symbiotic relationship in which both benefit.
coral anemone

The delicate balance inherent in these relationships among organisms is at the crux of life on Earth. Understanding how they work, and how they change over time, is critical to our knowledge of biology.

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