Everywhere you look on Earth, you’ll find wonderful and diverse living things, from tiny tardigrades to soaring sequoias. And incredibly, everything alive today, and everything that’s ever lived, is related. In this episode of Crash...

How can you tell two species apart? It’s not always simple. In this episode of Crash Course Biology, we’ll learn about speciation—a process that can happen over millions of years, or within a single generation. Along the way, we’ll...

Paul Andersen explains the concept of coevolution. He begins with an analogy comparing the relationship of humans to technology with those of coevolving species. He then discriminates between coevolution and convergent evolution. He...

Paul Andersen reviews the major components of the homeostasis. He explains how organisms respond to abiotic and biotic factors in their environment with feedback loops. He shows how responses can be behavioral or physiological.

Paul Andersen introduces the concept of bioenergetics. He explains how living organisms utilize free energy in the Universe. He begins with a brief discussion of thermodynamics and Gibbs free energy. He then explains how reactions can...

Paul Andersen explains how the behavior of various organisms is shaped by natural selection. The action of phototropism and the timing of photoperiodism have both been shaped by the relative availability of light. Courtship in the...