Life is bacterial and those organisms that are not bacteria have evolved from organisms that were. ...Gene exchanges were indispensable to those that… - Lynn Margulis

Not only did life originate on earth very early in its history as a planet, but for the first two billion years, Earth was inhabited solely by bacteria.

The fundamental division of forms of life on Earth is not that between plants and animals, as is commonly assumed, but between prokaryotes—organisms composed of cells with no nucleus, that is, bacteria—and eukaryotes—all other life forms.

I work in evolutionary biology, but with cells and microorganisms. Richard Dawkins, John Maynard Smith, George Williams, Richard Lewontin, Niles Eldredge, and Stephen Jay Gould all come out of the zoological tradition, which suggests to me that, in the words of our colleague Simon Robson, they deal with a data set some three billion years out of date. Eldredge and Gould and their many colleagues tend to codify an incredible ignorance of where the real action is in evolution, as they limit the domain of interest to animals... very tardy on the evolutionary scene, and they give us little real insight into the major sources of evolution's creativity. By "codifying ignorance" I refer in part to the fact that they miss four of the five kingdoms of life... bacteria, protoctista, fungi, and plants.