Books and Arts

Nature 425, 767-768 (23 October 2003) | doi:10.1038/425767a

The eyes have it

Richard E. Lenski1

BOOK REVIEWEDLife's Solution: Inevitable Humans in a Lonely Universe

bySimon Conway Morris


Cambridge University Press: 2003. 464 pp. £18.95, $30

The eyes have it

AL GRANT

The late Stephen Jay Gould argued that evolution is unpredictable. His thought-experiment of replaying life's tape, in Wonderful Life (W. W. Norton, 1989), led him to assert: "Alter any early event, ever so slightly and without apparent importance at the time, and evolution cascades into a radically different channel." The aim of Life's Solution is to overthrow that historically contingent view of life. What is at stake, according to its author Simon Conway Morris, is more than the statistical mechanics of evolution: at stake is how we understand our place in the Universe.

Life's Solution builds a forceful case for the predictability of evolutionary outcomes, not in terms of genetic details but rather their broad phenotypic manifestations. The case rests on a remarkable compilation of examples of convergent evolution, in which two or more lineages have independently evolved similar structures and functions. The examples range from the aerodynamics of hovering moths and hummingbirds to the use of silk by spiders and some insects to capture prey.

Convergence is widespread, despite the infinitude of genetic possibilities, because "the evolutionary routes are many, but the destinations are limited", as Conway Morris puts it. Certain destinations are precluded by "the howling wildernesses of the maladaptive", where the vast majority of genotypes are non-viable and prevent further exploration by natural selection. Conway Morris is spectacularly successful at tracking down and organizing examples of convergent evolution, but he admits that work to place convergences "into any sort of quantitative framework is still in its infancy". In effect, he emphasizes the numerator (convergence) while skirting the denominator (all examples of evolution, both convergent and divergent).

Conway Morris is not content, however, to catalogue examples of convergent evolution. He wants to convince us that convergence implies the inevitability that some sentient human-like being will evolve on any life-bearing planet like Earth. Thus, he focuses his compilation on the attributes we associate with ourselves and the lineage that produced us. Fruiting bodies of slime moulds and myxobacteria show that multicellularity has evolved repeatedly. Warm-bloodedness evolved several times, as did live birth and even penile tumescence. Sensory organs exhibit numerous cases of convergence: the eyes have it, as seen in the camera-like eyes of vertebrates and octopuses, and the similar eyes of certain worms and jellyfish. So, too, mechanisms used by diverse organisms to smell, hear, echolocate, sense electrical fields and maintain balance are often convergent.

Complex social systems have evolved repeatedly, exemplified by termites, ants and mole-rats. Fungus-farming ants and tool use by crows remind us that even agriculture and invention have evolved elsewhere. Just as the availability of light to guide organisms has led repeatedly to the evolution of eyes, the acquisition of complex information about an organism's environment implies selection to better store and use the information. The evolution of extra-large brains and corresponding intelligence in dolphins and primates illustrates that convergence. Conway Morris stops short of saying that another species has yet evolved the sophisticated language of humans, but suggests that "waiting in the wings of the theatre of consciousness are other minds stirring, poised on the threshold of articulation". These are provocative words and, whether or not one agrees with his conclusions, the examples are fascinating and indicate a prodigious knowledge of the scattered literature on convergent evolution.

Given this rampant convergence here on Earth, Conway Morris believes that "extraterrestrials with nervous systems will hear, see, and smell in very much the same way as we do, and if that is so will also possibly have similar mental processes". So where are these ETs? Alas, he doubts that they exist. Conway Morris and Gould both think that we humans might be alone, but for different reasons. For Gould, "the awesome improbability of human evolution" derives from contingency in adaptive evolution. Conway Morris argues that if our planet were even slightly different from the way it actually is, then life might not have emerged. His argument is based on the difficulties of getting life started, on the failure of scientists to synthesize life from scratch, and on some unusual features of Earth and our Solar System. He even suggests that intelligence might never have evolved here had not a cataclysmic impact jettisoned the Moon into its orbit. This sounds rather like Gould's historical contingency, except that Conway Morris emphasizes physical events creating opportunities for life to emerge and adapt, whereas Gould emphasized the idiosyncratic nature of adaptation itself.

The tension between inevitability and loneliness leads Conway Morris towards a higher objective, which is to re-establish "notions of awe and wonder" in evolution and thus "allow a conversation with religious sensibilities". He dismisses Fred Hoyle's "strange ideas about the origins of biological complexity" but admits a grudging respect for Hoyle's remark that the Universe is a "set-up job". Conway Morris's metaphysical vision occasionally becomes overwrought, as when he says: "Not only is the Universe strangely fit to purpose, but so, too, as I have argued throughout this book, is life's ability to navigate its solutions." Whatever Conway Morris may think about the Universe and its predispositions, Life's Solution invokes the standard darwinian explanation of adaptation by natural selection for life's ability to navigate.

I recommend this book to anyone grappling with the meaning of evolution and our place in the Universe, and to biologists interested in adaptation and constraints. I am obliged, however, to caution readers about the deprecating way in which Conway Morris sometimes refers to evolutionists whose views he opposes. He is especially dismissive of Gould, who died a year ago: readers interested in their conflict can read an exchange elsewhere (Natural History 107, 48–55; 1998). Conway Morris's antagonism to Gould becomes more puzzling when one reads — in a chapter titled "Towards a theology of evolution?" — of his disdain for "ultra-Darwinists" and "genetic fundamentalism", as these were also frequent targets of Gould's pen. But while Gould argued for the separation of science and religion, Conway Morris is searching for common ground.

Conway Morris derides the "almost gleeful abasement of humans" by ultra-Darwinists, and claims that Darwin himself "retreated into a gloomy agnosticism". But the closing passage of The Origin of Species is far from gloomy: "There is grandeur in this view of life, with its several powers having been originally breathed into a few forms or into one; and that ... from so simple a beginning endless forms most beautiful and most wonderful have been, and are being, evolved." In the second edition Darwin inserted three words (italicized here): "... breathed by the Creator". In Life's Solution, Conway Morris has perhaps explained why, in his view of life, the second edition might be preferable to the first.

  1. Richard E. Lenski is in the Department of Microbiology and Molecular Genetics, Michigan State University, East Lansing, Michigan 48824, USA.