Carl Zimmer in his excellent blog, The Loom:
Every creature from a microbe to a mountain lion can respond to its surroundings. E. coli has sensors on its surface to detect certain molecules, and it processes those signals to make very simple decisions about how it will move. It travels in a straight line by spinning long twisted tails counterclockwise. If it switches to clockwise, the tails unravel and the microbe tumbles.
A worm with a few hundred neurons can take in a lot more information from its senses, and can respond with more behaviors. And we, with a hundred billion or so neurons in our brains have a wider range of responses to our world.
A group of scientists from Caltech, the University of Wisconsin, Michigan State University, and the Allen Brain Institute wanted to better understand how this complexity changes as life evolves. Does life get more complex as it adapts to its environment? Is more complex always better? Or–judging from the abundance of E. coli and its fellow microbes on the planet today–is complexity overrated?
More here.