Excerpt from The Sixth Extinction

From Richard Leakey and Roger Lewin:

“…There was no steady progression from simple to complex forms throughout Earth history. Simple forms of life arose early on, it’s true. But…that early simplicity continued in mind-numbing sameness for billions of years, with nothing more complex than singe-celled organisms for six sevenths of Earth history. When complexity eventually arose 530 million years ago, in the form of multicellular organisms, it did so explosively; within 5 million years (an instant in geologic time), evolutionary innovation produced a myriad of multicellular forms of life. Life’s flow is therefore not smooth, but extremely erratic.”