Plot summary

The episode covers several facets of the origin of life and evolution. Tyson describes both artificial selection via selective breeding, using the example of humankind's domestication of wolves into dogs, and natural selection that created species like polar bears. Tyson uses the Ship of the Imagination to show how DNA, genes, and mutation work, and how these led to the diversity of species as represented by the Tree of life, including how complex organs such as the eye came about as a common element.

Tyson describes extinction of species and the five great extinction events that wiped out numerous species on Earth, while some species, such as the tardigrade, were able to survive and continue life. Tyson speculates on the possibility of life on other planets, such as Saturn's moon, Titan, as well as how abiogenesis may have originated life on Earth. The episode concludes with an animation from the original Cosmos showing the evolution of life from a single cell to humankind today.