Carl Zimmer has published an excellent, must read essay for anyone the least bit curious about biology and the origins of life. It covers the ongoing questions about the origin of eukaryotes in terms of their relationship to prokaryotes and archaea, and how different components critical to success, such as the membrane enclosed nucleus and mitochondria, came to be.
Prokaryotes can generate energy only by pumping charged atoms across their membranes. That constraint helps limit their size. As prokaryotes grow in size, their volume increases much faster than their surface area. They end up with too little energy to power their cells. Eukaryotes, on the other hand, can pack hundreds of energy-generating mitochondria into a single cell. And so they could get big, evolving into an entirely new ecological niche. “You don’t have to compete for the same nutrients,” says Nick Lane of University College London, author of Life Ascending: The Ten Great Inventions of Evolution. “You simply eat the opposition.”
The entire essay is written in a straightforward, simple style so that someone without a science background can understand it without struggling.