What Is Biology?

Cell division stages of mitosis

Biology is the study of living things. Whether they are animals, people, plants or microscopic organisms, if it is alive, it falls under the umbrella of biology. Biology is a component of the broader study of life sciences, but life sciences also include disciplines such as medicine, or other applied and interdisciplinary studies that blend biology and technology together.

Major Theories in Biology

Of course, scientists work with many theories and hypotheses, but there are four major theories on which modern biology is based.

Cell Theory

When early scientists first developed and used a microscope, they were surprised to find that living things appeared to be made of tiny 'blocks.' These 'blocks' today are known as cells, but those early experiments form the basis of cell theory:

  1. All living things are made up of cells.
  2. Cells are the basic unit of structure and function of all living things.
  3. Living cells can only come from other living cells.

Evolution by Natural Selection

There are few students who have studied biology that haven't heard of Charles Darwin and his experiments on the Galapagos Islands. His observations there led him to develop the theory of evolution and form the basis of much of what scientists understand about the natural world today. The theory has several main components:

  1. There is a variation of traits. For example, consider the hypothetical case of green butterflies and brown butterflies.
  2. Not all animals get to reproduce to their fullest potential. Using the butterfly example, green butterflies tend to get eaten by predators because they cannot easily camouflage themselves, whereas the brown butterflies blend in against their habitat.
  3. Offspring inherit genetic traits. With the butterflies, the remaining brown butterflies have brown butterfly offspring, thus creating a butterfly population that is more likely to survive longer because it is less susceptible to prey.
  4. More advantageous traits eventually win out over less advantageous traits. In this case, eventually, most of the butterfly population would be brown because it's genetically advantageous.

Gene Theory

Rainbow dna

Beginning with Gregor Medel and his pea plant experiments, gene theory is simply the idea that the gene is the unit of inheritance. While it has been modified many times in modern years as scientists discover more information, the premise that all living things have genetic code that is passed down to offspring is the cornerstone of modern genetics.


Homeostasis is a theory that explains how everything autoregulates by maintaining an equilibrium. For example, your body responds to external stimuli to maintain a fairly constant temperature. If your body gets too hot, you will sweat; if you get too cold, your body shivers. Cells also maintain an equilibrium by controlling what substances can come in and out of the cell. These are common examples of the theory of homeostasis at work, but any process that is used to maintain equilibrium for a living thing's survival is homeostasis.

Major Fields of Study and Careers

Biologists can go into a variety of careers and fields of study. There are many types of biology and many areas in which scientists can delve, however the following are some of the broader areas.

Molecular Biology

Woman holding science model

Molecular biologists study cells and are especially concerned with how molecules and cells operate, organize, and communicate. They pay special attention to how molecules control a cell's activity and growth. Molecular biologists can do a variety of things ranging from working in agriculture to working in genetics.

Cellular Biology

As the name implies, cellular biologists study cells. They focus on healthy and diseased cells, which helps develop new medicines, create disease-resistant plants, or create new vaccines. In addition to working in laboratories, cellular biologists could work with food, plants, animals, or people.


Geneticists study how traits are inherited. There is a variety of avenues geneticists can pursue as a career ranging from forensics to botany to history and archaeology to biomedicine.

Developmental Biology

fetus at 9 weeks

Developmental biologists study how organisms grow and develop. Developmental biologists ask questions like how does something as simple as a cell grow into something complex like a person, or they investigate how to use stem cells or how to clone cells.


Physiologists study anatomy, and while there are many types of physiology, such as plant and animal, when people describe themselves as a physiologist, they mean that focus on human anatomy. Physiologists deal with all sorts of questions relating to human anatomy; popular topics currently include exercise physiology and brain physiology.

Evolutionary Biologists

Evolutionary biologists are interested in how species change over time, and they look at how species are related genetically as well. While their work is largely based in research, it spans a wide variety of disciplines.

Environmental Biology

seedlings sprouting

Ecologists and environmental biologists study the effects of interactions (generally human) have on the planet on the environment. It spans a variety of disciplines and can be applied to almost any living thing living in any habitat. Environmental biologists may do a variety of jobs like figuring out how to preserve habitats or figuring out the best way to clean up from an environmental disaster.

Biology Is Foundational

Biology is the foundation of many sciences, technological advances, and interdisciplinary methods of studying. It's typically the first science you learn and has applications in just about all the other types of sciences out there.

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What Is Biology?