Simon Conway Morris is the Emeritus Professor of Evolutionary Palaeobiology at the University of Cambridge. Dr. Morris is well known for his work on the early evolution of metazoans (popularly referred to as the “Cambrian Explosion”) and his extensive studies on convergent evolution. He is the author of more than 100 scientific articles and is the author or editor of seven books. These include The Crucible of Creation: The Burgess Shale and the Rise of Animals (Oxford University Press, 1998), Life’s Solution: Inevitable Humans in a Lonely Universe (Cambridge University Press, 2003), and The Runes of Evolution: How the Universe became Self-Aware (Templeton Press, 2015). Dr. Morris has received the Walcott Medal from the National Academy of Sciences, the Charles Schuchert Award from the Paleontological Society, and the Lyell Medal from the Geological Society of London. He was elected a Fellow of the Royal Society in 1990. He has spoken extensively at the intersection of science and religion, including giving the Gifford Lectures in 2007 at the University of Edinburgh.

CHAPTER 1

CHANCE AND NECESSITY INEVOLUTION

Richard E. Lenski

Introduction

We humans have long recognized the profound tension that existsin our world between chance and necessity, between things thatseem to happen by accident and those that seem inevitable oreven purposeful. Democritus said that "everything existing in theuniverse is the fruit of chance and necessity." The aphorism that"necessity is the mother of invention" finds its counterpoint inMark Twain's quip that "necessity is the mother of taking chances."Even in our most goal-directed endeavors, we see the tensionbetween accident and purpose, as Louis Pasteur did in saying that"chance favors only the prepared mind."

My intention in writing this chapter is not to sort out the tanglednuances of the words chance and necessity. Nonetheless, itmight be helpful to illustrate some of these nuances before proceeding.Chance often invokes some instantaneous disturbance,such as a cosmic ray striking a chromosome and causing a particularmutation. Chance is also sometimes used with reference tocontingent effects of prior historical events, such as how the courseof life on Earth might have unfolded differently had some asteroidnot caused a certain mass extinction. Yet, the cosmic ray may havefollowed a path set by the laws of physics, and the historical influencesmight have been inevitable in their time. What the notionof chance captures is the sense of unpredictability and the absence of controlexerted by the affected system over its own eventual fate.

Necessity is fraught with even more divergent meanings. Necessity isoften used to describe outcomes that are inevitable given the action ofphysical laws, such as the motion of one billiard ball that has been struckby another ball at a particular angle and momentum. Necessity can alsorefer to a purposeful course of action, one that must be followed in orderto achieve some desired end, such as striking one ball with a cue so thatit hits another ball at the angle and momentum that is required to movethe second ball in a particular way. And in an evolutionary context, necessityprovides a shorthand term to describe adaptive solutions, produced bynatural selection, that allow organisms to cope with the various challengesthey face in their environments. The hand-eye coordination that enablesthe pool player to strike a ball precisely as intended might be an adaptationthat was necessary for survival during some part of the history of ourspecies. (Ayala [1999], Pennock [1999], and Ruse [2003] discuss importantsimilarities and differences between designs produced by the deliberateactions of conscious agents and those that result from natural selection.)

The Roles of Chance and Necessity in Evolutionary Thought

The tension between chance and necessity is perhaps more central to evolutionarybiology than to any other science. Physics certainly encompassesthe determinism of classical mechanics and the randomness of quantummechanics, but these forces play out at such different scales that the difficultylies in linking these two realms rather than in disentangling theireffects. By contrast, the tension between chance and necessity enters intocurrent evolutionary thought at two levels that are both central to ourunderstanding of the biological world in which we live.

At one level, we have the historical narrative of life on Earth that is theprimary focus of paleontological and much comparative research. It is agreat struggle, of course, to sort out what happened and when, especiallyacross the vast reaches of time. Nonetheless, things really did happen andat certain moments. Thus, there is only one true history that occurred,although we will never be able to reconstruct it in its entirety. But justas students of human history are fond of asking how things might haveunfolded differently if some past event were altered, so too evolutionarybiologists are fascinated by similar questions. Stephen Jay Gould, in WonderfulLife (1989), offered the thought experiment of "replaying life's tape"to evoke these what-if questions in the context of evolution. What if differentanimal phyla had survived the Cambrian than those that did? Whatif an asteroid had not hit Earth at the end of the Cretaceous? Or whatif the asteroid had been half the size, or twice the size, of the one thatactually hit? For that matter, what if it had hit just one hour sooner orlater? What difference would these accidental circumstances have made tothe subsequent evolution of life, including our own coming into being?For Gould, the quirks of history and the immensity of alternative pathsled him to infer the "awesome improbability of human evolution"—notonly in the narrow sense of our particular species but more generally inthe sense of any species that can wonder and reason about its own origins.Most evolutionists accept Gould's conclusion in the narrow sense,but others have argued against his more general conclusion. Simon ConwayMorris (2003) presents myriad examples of parallel and convergentevolution, whereby multiple lineages have independently evolved...