Michael Shermer

>From Chapter 10, "Glorious Contingency," of How We Believe: The
>Search For God in an Age of Science (www.howwebelieve.com),
>published by W. H. Freeman.

Glorious Contingency: A Little Twig Called Homo sapiens

The model of contingent-necessity and its corollaries is a formalization of Gould's dangerous idea. In an essay entitled "Fungal Forgery" (1993), Gould applied the model to a complex insect-flower system to show how it could have evolved, but in a very unpredictable manner in its early stages: "Fungal pseudoflowers are late necessities, and they give us no reason to suppose that the complex contingent prerequisite for this sensible story--the evolution of the insect-flower system--has any similar predictability." Before turning from this fascinating particular to broader generalities about contingency, Gould offered his usual caveat: "I do not, of course, deny that the history of life includes predictable events and recurrent patterns. I do, however, suspect that most predictable aspects of life lie at too 'high' a level of generality to validate what really stirs and troubles our souls--the hope that we might ratify as a necessary event the evolutionary origin of a little twig called Homo sapiens." But beyond such anthropomorphic concerns, Gould shows why necessities may not always dominate:

"As an interesting consequence of Shermer's model, we may ask why life as a whole doesn't finally settle down to globally predictable unrolling, whatever the massive contingency of initial stages. Shermer points, correctly I think, to the importance of infrequent and highly disturbing events (such as mass extinction for faunas or punctuated equilibria for lineages) in derailing the stasis or predictable unrolling of systems otherwise stabilized. The theoretical importance of rare, and sometimes cataclysmic, events --
as the preservers and reinvigorators of global contingency--may best be appreciated in the light of such historical models."

Gould then returns to his familiar metaphor of the tape, applying the model to the entire history of life:

"But if I could rerun the tape of life from the origin of unicellular organisms, what odds would you give me on the reevolution of this complex and contingent insect-flower system? Would we see anything like either insects or flowers in the rerun? Would terrestrial life originate at all? Would we get mobile creatures that we could call animals? Fine-scale predictability only arises when you are already 99 percent of the way toward a particular result -- and the establishment of this 99 percent lies firmly in the domain of unrepeatable contingency."

The contingent evolution of insect-flower systems, however, is not what makes contingency dangerous. It is that contingent little twig called Homo sapiens that tasks us. We want to be special. We want our place in the cosmos to be central. We want evolution--even Godless evolution--to have been directed toward us so that we stand at the pinnacle of nature's ladder of progress. Rewind that tape of life and we want to believe that we (Homo sapiens) would appear again and again. Would we?

Most likely not. There are simply too many contingent steps along the way, too many trigger points where the sequence could have bifurcated down some other equally plausible path. Alfred Russel Wallace, the co-discoverer of natural selection, toward the end of his life realized this in his book, Man's Place in the Universe (1903, 73):
"The ultimate development of man has, therefore roughly speaking, depended on something like a million distinct modifications, each of a special type and dependent on some precedent changes in the organic and inorganic environments, or in both. The chances against such an enormously long series of definite modifications having occurred twice over are almost infinite." And Wallace did not know what we know about human evolution: his "million distinct modifications" is probably off by an order of magnitude. We now know that human evolution goes back millions of years, and that is just for the lineage leading to us. What if we rewound the tape to include the evolution of all primates, or all mammals, or all life on Earth? Trillions of distinct modifications over the last three billion years since life began would need to proceed along similar lines to produce our little twig a second time.

Is the cosmos itself so contingent? If we rewound the tape back to the beginning of the universe would there be another Big Bang, another universe just like ours? No one knows, but if recent cosmological models pan out it would appear that there are a near infinite number of bubble universes all with slightly different laws of nature. Chances are another universe like ours would reappear, which means that galaxies like ours with stars like ours would form again and again. Recent evidence also leads us to believe that planetary formation is a commonplace event in the galaxy. It is still a little soon to be drawing any definite conclusions, but with enough stars (roughly 400 billion in our galaxy alone), chances are there will be other Earth-like planets, maybe hundreds of thousands of them, the right distance from the home star to give rise to life. It would appear that physical systems are more governed by necessity, while living systems are more governed by contingency.

But this is oversimplifying matters. The actual evolution of life on a planet is really governed by contingent-necessity, and since we cannot remove living organisms from their physical environment, these relative estimates of potential "other Earths" depend on when in the sequence the tape begins again. Moreover, since no one really cares about whether cockroaches would reappear, let's cut to the chase and ask whether a primate species with a big enough brain to have consciousness, symbolic language, religion, awareness of its own mortality, and a developed enough system of thought to ask this very question, would evolve again. We cannot run the experiment, of course, but we do not need to because history has done it for us. The fossil record, while still fragmented and desultory, is complete enough now to show us that over the past thirty million years we can conservatively estimate that hundreds of primate species have lived out their lives in the nooks and crannies of rain forests around the world; over the past ten million years dozens of great ape species have forged specialized niches on the planet; and over the last six million years, since the hominid split from such great apes as gorillas, chimps, and orangutans occurred, dozens of bipedal, tool-using hominid species have struggled for survival.

If these hominids were so necessitated by the laws of evolutionary progress, why is it that only a handful of those myriad pongidids and hominids have survived? If braininess is such an inevitable product of necessitating trends of nature, then why has only one hominid species managed to survive long enough to ask the question? What happened to those big-brained hominids Homo habilis, Homo rudolfensis, Homo ergaster, Homo erectus, Homo heidelbergensis, and Homo neanderthalensis? If big brains are so great, why did all but one of their owners go extinct (including the Neanderthals whose brains were slightly larger than our own)? And before them, what happened to the bipedal, tool-using Australopithecines: anamensis, afarensis, africanus, aethiopicus, robustus, boisei, and, most recently, garhi? Discovery after discovery coming out of Africa reveals our ancestors to be puny little small-brained creatures walking upright, using tools, and eating meat, allegedly the ingredients that go into making big brains. If necessitating evolutionary progress were so potent then why aren't there a dozen modern human-like species that should have arisen out of these Australopithecine ancestors? Historical experiment after experiment reveals the same answer: we are a fluke of nature, a quirk of evolution, a glorious contingency.

-- Michael Shermer

Published   2000.03.12