Challenging Nature
published by Ecco/Harper Collins, 2006
Professor of molecular biology and public policy in the Woodrow Wilson school of Public & International Affairs at Princeton University
Lee Silver photo
Princeton Courses
July 2006
Think only the religious right is anti-science? How about the spiritual left?
By Lee M. Silver
From the book CHALLENGING NATURE: The Clash of Science and Spirituality at the New Frontiers of Life. © 2006 by Lee M. Silver.
Published by arrangement with HarperCollins Publishers.
Strangler fig
Germinating in the ground and growing in utter darkness for a long span of time is a difficult task for a tree seed to pursue successfully, but I didn't think they had much choice based on my experience living in the northeastern part of the US. In the rainforest, however, many enormous centurial trees began their existence with a head start of 100 feet or more toward the sun. The life cycle of these strangler figs, as they are called, is startling to anyone who imagines Mother Nature to be a harmonious place, especially for greenery. The fruit of the strangler figs is a favorite of rainforest monkeys, who swallow the small watermelon-like seeds. Later, they defecate a pile of seed-containing dung that becomes trapped in a corner between two branches of another tree high up in the forest. The warm dung acts as potent fertilizer and the seed germinates into a rootless vine with appendages that slowly crawl up and down along the trunk and branches.
When the downward appendages hit the ground, their tips turn into roots which absorb larger amounts of water from the mud and distribute it to the rest of the fig organism. The appendages themselves now begin to expand sideways as they wrap themselves around the inner tree's trunk and major branches. Eventually, the original tree is engulfed and disappears. The fig tree, with its hidden hollow center, has killed and taken the place of the host that brought it to life. A walk through the Amazon or any other rainforest in Central America, Asia or Africa will provide you with abundant seemingly-static snapshots of each stage in this slow lethal process.
The strangler fig is not the exception but, rather, the rule of the jungle. Nearly every tree is weighed down by vines of different kinds that grow to enormous sizes. Old vines are themselves encrusted with other vines (which are themselves encrusted in moss and fungus). Leaves are eaten by caterpillars or destroyed by leaf-cutting ants. External termite nests, some larger than a person, hang from most older trees, themselves dotted with holes drilled by birds to eat insects living within. Heavily weighted and weakened branches struggle for survival, but eventually lose and break off.
It's not a good idea to wander off the trail into the thick undergrowth, our guide Ramiro tells us; if you're not bitten by a hidden venomous snake, your ankles will be attacked by marauding toxin-injecting ants, or your exposed hands could rub up against poison-covered plants. It's fine to go swimming in the river, he says, unless you're a menstruating woman or otherwise bleeding, in which case, hordes of piranhas will eat your flesh - down to the bone if you don't get out of the water while you can. Shallow lakes may be piranha-free, but they sprout leeches, which attach to your limbs and suck out your blood. And the air itself is thick with mosquitoes that stick a dirty needle-like proboscis through the exposed skin of any hot-blooded animal they can find. Sometimes they carry a hitchhiking protozoan killer that slides into blood cells to feed and reproduce wildly; the blood-borne offspring are picked up by other biting mosquitoes, leaving you behind to suffer from malaria and possible death. Everywhere you look, organisms suck the life out from organisms beneath them, just as they are consumed by organisms on their own backs. Ramiro sums it up in one of the many pithy aphorisms that cross his lips each day, "life in the jungle is fast and short."
It is not just other living things that can cause pain and suffering among human beings and other animals. Mother Earth herself can be entirely capricious and uncaring. Once upon a time, there was a forested paradise as big as the United States with an abundance of trees, including giant shade-providing acacias and hackberries, and verdant green shrubbery and grasses.1,2 The drenching rains were heavier in the summer, although the humidity was high all year long. Dotting the countryside were freshwater lakes and rivers with an abundance of fish. Along the shores, and in the shallows, antelopes, giraffes, elephants, and hippopotamuses lingered. Occasionally lions and tigers came out of the forests and made their presence known. Sophisticated civilizations of people were here too, raising cattle, hunting wild game, and planting crops. On the rock walls, they painted pictures of themselves engaged in these and other common activities. Throughout this vast homeland, for hundreds of generations, life was good.
Then, over the course of a few centuries, the unthinkable happened.1 The old men noticed that summers were now cooler and less rainy than in their childhood. The forests were becoming less dense, and the lake shorelines had receded drastically. By the time the grandchildren of the old men had grown up, the rains stopped completely, the lakes and rivers dried up, and the verdant forests dissolved into a vast desert of sand covering up all the villages. The gods must be angry, the people thought, because we did something wrong. Most perished, but a few escaped through migration to the northern coast, and others walked into an eastern river valley where water from a distant source continued to flow. But kept alive in the stories told by mother to daughter and father to son, from every subsequent generation to the next, even until our present day, is the legend of God's eviction of disobedient human ancestors from the ancient Garden of Eden.
The foundation for the story just told is not a fairytale, or a warning of the ecological devastation that will descend upon the earth if human beings don't mend their ways. In its broadest strokes, these events really did unfold - in the place we call the Sahara, now the largest and driest desert in the world. Between 13,000 BC and 3,500 BC (an era named the African Humid Period by earth scientists), the climate and ecology of the Sahara was radically different than it is today.3 Ironically, for those not spiritually inclined, the blame for the capricious climate can be put squarely on the shoulders of Jupiter - not the god of gods, but the planet.
The African Humid Period occurred when the Northern hemisphere was both maximally tilted and maximally close to the summer sun. Hotter air from the north forced sustained intense heat to cover the Sahara at ground level. Hot air is less dense and rose more quickly sucking heavy Atlantic rain clouds in its stead. Rain initiated the growth of green life, which absorbed the sun's heat more effectively than bare ground. As forests grew, they retained more heat and humidity, causing the rains to become more intense.
These Eden-like conditions lasted for almost 10,000 years. And then, as the earth continued to cycle through natural changes in orbit and spin, the entire system collapsed. Less midday summer sunlight in the North produced less heat, which led to weaker winds, which led to less rain, which led to a thinning of the forest, which led to a lower capacity for heat absorption, and so on.3 The Sahara forest may have spiraled into an arid abyss in less than a century and a half, a blink of the eye in geological terms, although long enough for some people to migrate elsewhere.4 Circumstantial speculation suggests that they could have brought their rich culture into the Nile Valley, setting the stage for the sophisticated and long-lasting classical Egyptian civilization. Whether the green Sahara was the inspirational source for the Biblical Garden of Eden, we'll never know.
What I find most remarkable about this fascinating story is that it is practically unknown outside specialized fields of climatology and anthropology, although scientists have been writing about it for over 40 years. In contrast, everyone knows about Ice Ages of the past, which are no more dramatic than a green Sahara. The distinction seems to be that the Sahara's past reveals a truth modern people don't want to hear: Mother Nature can be a nasty bitch.
Post-Christian western cultures, in particular, want to believe in a Mother Nature that is feminine and benevolent, always promoting her biosphere in positive ways. Life will thrive unless, according to Greenpeace International, foolish human beings persist in "... throwing the world's climate out of its natural balance and into chaos."[my emphasis]5 The assumption is that if we just left Mother Nature alone to follow her own path, everything would turn out for the better. The retreat of the glaciers, which led to the blossoming of human civilization, is consistent with this view. A once-upon-a-time green Sahara wiped out by natural - not human-induced - climate change doesn't fit the whole-earth spiritual picture, and does not become incorporated into the public consciousness.
What if biotechnology could be deployed to sustain and expand a self-regenerating Sahara forest that could benefit humankind in many ways? Ecological alterations of such large magnitude - whether natural or human-induced - always have effects on other regions of the globe. Computer modeling will help future societies determine whether a green Sahara would be better or not for humankind and the biosphere as a whole. The ultimate question, though, is who should we trust to make such future choices: global society or Mother Nature? Mother Nature, without our help, turned gigantic vibrant ecosystems into lifeless deserts. Mother Nature, without our help, "ruined ancient civilizations and socio-economic systems."6 Mother Nature, without our help, covered Canada in mile-deep glaciers, and she would certainly do it again if all human industry disappeared.
Who or what benefits from the massive and perpetual orgy of organic churning and decimation that is Mother Nature? Certainly not the individual victims; which includes the vast majority of plants and animals in the rainforest and everywhere else. Few survive long enough to die "naturally" from old age. Even many of the so-called "top-of-the-food chain" predators like the elusive Amazonian jaguar, that walked past our tent one night, are done-in by tiny parasites or same-species competitors. What most people in Western society believe today is that the benefit accrues to the "ecosystem as a whole."
You don't have to look far to discover how this concept is taught and reinforced from early childhood. The first page of the first chapter of the Prentice Hall Ecology textbook used by my son's 5th grade class focuses on a tender story of ants and aphids opposite a full-page picture of their peaceful lives together:
"Upon reaching the aphid, the ant begins to stroke the smaller insect with its feelers. The aphid responds by releasing a drop of a sugary substance called honeydew. The ant eagerly licks up the honeydew. Then the ant gently picks up the aphid in its jaws and carries it to another leaf. There the aphid is added to a 'herd' tended by ants. The ants take care of the aphids in exchange for meals of honeydew." 7
Educated adults are also bombarded with a holistic image of life on earth. In 1970, the scientist James Lovelock used an understanding of atmospheric chemistry to argue for the recognition of the biosphere as a "unified self-regulated organism," christened Gaia (from the earth-mother goddess of Greek mythology) with component parts that work together symbiotically for the good of the whole. If Gaia is used simply as a value-neutral metaphor to describe the entire complex network of symbiotic interactions over the history of our planet, no evolutionary biologist or ecologist would complain. But when Gaia moves from the science sphere to the public sphere, it becomes translated into something entirely different.
How does an emotional attachment to the spirit of Mother Nature color one's views concerning the morality of using biotechnology to genetically alter plants and animals for the benefit of humankind, or the biosphere itself?
The problem begins with the popular meaning of the word symbiosis. Scientists use the word broadly to describe any biological interaction between species that provides benefit to one or both. Parasitism - in which individuals from one species gain a benefit at the expense of another's life or longevity - is, by far, the most common form of symbiosis. To the public, however, symbiosis is considered to be a synonym for community and cooperation among individuals.8 And so when Lynn Margulis, the most important scientist-popularizer of Gaia, titles her book on the subject Symbiotic Planet, the take-home message seems clear: all of the organisms on earth cooperate unconsciously to keep alive a unified Gaia or Mother Nature, who is more conscious than her individual plant and animal parts.
To get a sense of how common this vision is at a university not known for attracting students with counter-culture beliefs, I placed the following question on an anonymous survey of Princeton undergraduates: Can a species, an ecosystem or another grouping of multiple organisms have a unified spiritual soul? The possible answers were: (a) No, it makes no sense to say that a system of multiple organisms has a spiritual soul; (b) Yes, some systems of multiple organisms (e.g. species, ecosystem, or biosphere) can have a unified spiritual soul; or (c) I am not sure whether systems of multiple organisms can have a spiritual soul.
Multi-organismal spirits are incompatible with both Christianity (the religion with which over 85% of Princeton students self-identify) as well as the science instruction these students received even before they were admitted to my university. And yet, only 48% of female students and 61% of men felt confident enough to reject the idea outright.9 Among female humanities majors, the proportion dropped to 36%. The results (surprising to me) imply that even in America, where traditional Christianity is still a powerful force, highly educated young people are attracted to the post-Christian worldview of a unified "Mother Nature" that is more than a metaphor.
Can we really determine - from our perspective as potential component parts - whether the whole biosphere, or even an isolated ecosystem, behaves like a single organism? Is it possible that each species in the rainforest really is analogous to a nerve cell or ant whose work and activities serve the goal of something that only comes into existence through the proper functioning of the much larger whole? One way to approach this question is by comparing the actual design of ecosystem networks with the design of other types of biological networks.
Three wholly different levels of biological organization are observed in nature. At the bottom, specific interactions among genes and protein molecules give rise to the emergent property of dynamic life within each single cell. In network language, each type of molecule can be viewed as a node and each type of molecular interaction as a connection. Animals are also made up of cells, but a higher level of organismal life emerges when multiple cells interact with each other to form a brain that produces a mind of some kind. In network language, brain cells are nodes, and synapses are connections. Finally, the highest level of biological organization occurs in an ecosystem where species can be viewed as nodes, and symbiotic relationships are represented as connections.
In 2002, the Israeli scientist Uri Alon and his colleagues at the Weizmann Institute performed a computer analysis of the architecture underlying 10 unrelated biological networks, including two species of cells (from different phylogenetic kingdoms), one completely described brain with 252 neurons, and seven very different ecosystems.10 Although the physical meanings of nodes and connections are entirely different in cells and brains, Alon found that cell networks and the brain network have the same architectural design which optimizes the flow of information among component parts. In other words, in all three organismal cases, components really are working for the good of the "whole" organism.
The architectures of all seven ecosystems are similar to each other, yet strikingly different from the biological networks found in cells and brains. In each eco-case, information flow among component parts (individuals of different species) is suppressed to a greater extent than expected from chance alone. This empirical result makes sense in theoretical terms because when every organism is a potential victim of a new parasite or predator species, it pays not to advertise yourself. There are exceptions, of course, in isolated instances of mutually beneficial symbiosis. But the clear implication is that different species do not work for the good of the whole community.
In fact, the natural world hews closer than any modern democracy to Adam Smith's laissez-faire model of human economic activity. Nature has no central authority of any kind to which species are beholden. Organisms don't abide by any rules of competition, and no safety net exists for losers. Through rational analysis alone, anyone able to accept the idea that a complex and "vibrant" economy can evolve in the absence of a unified spirit should also be willing to accept the idea that complex ecosystems can evolve in the absence of any overarching multi-organismal spirit of any kind. Yet, at an emotional rather than a rational level, non-scientists and scientists alike can sometimes be led astray by the holistic conceptualization of Mother Nature's creatures living primarily in peaceful harmony with each other.
If neither scientific theory nor scientific facts provide support for a coordinated Gaia super-organism, we are faced with two questions. First, whose interests are organisms working for if not Gaia? Second, how does an emotional attachment to the spirit of Mother Nature color one's views concerning the morality of using biotechnology to genetically alter plants and animals for the benefit of humankind, or the biosphere itself?
1. P. deMenocal et al., "Abrupt onset and termination of the African Humid Period: Rapid climate responses to gradual insolation forcing," Quaternary Sci Rev, 19:347-61, 2000;
2. R. Kunzig, "Memories of a lush Sahara," U.S. News & World Report, Oct. 13, 2003.
3. M. Claussen, "On multiple solutions of the atmosphere-vegetation system in present-day climate," Global Change Biol 4:549-59, 1998.
4. M. Claussen et al., "Simulation of an abrupt change in Saharan vegetation in the mid-holocene," Geophys Res Lett, 26: 2037-40, 1999.
5. Greenpeace, The Cause (accessed on July 12, 2004,
6. C. Arthur, "Tilt of earth's axis turned Sahara into a desert," The Independent, Sept. 8, 1999.
7. A. Maton, Ecology: Earth's Living Resources, Annotated teacher's ed., Englewood Cliffs, NJ: Prentice Hall, 1993.
8. The dictionary available with the 2001 Macintosh version of Microsoft Word provides two definitions of symbiosis: (1) a close association of animals or plants that is often, but not always, of mutual benefit; (2) a cooperative, mutually beneficial relationship between two people or groups. The Oxford American dictionary defines symbiosis as an "interaction between two different organisms living in close physical association, typically to the advantage of both."
9. The 335 students included in the survey were classified by gender (152 males, 155 females), and by area of major (118 science, 83 humanities, 84 social science, and 50 other). In answer to this particular question on multi-organismal souls, 16% of both males and females responded yes (B), 23% of men and 35% of women responded "I am not sure" (C), and 61% of men responded no (A).
10. Detailed schematic diagrams of the molecules and interactions within two unrelated species of single cell organisms have been determined: yeast with 686 nodes and the human gut bacterium E. coli with 424 nodes. To date, the complete architecture of a brain has been determined in only one species: the one millimeter long soil worm with 252 neuron nodes. Network diagrams have been determined for seven distinct ecosystems including both land and water habitats. R. Milo et al., "Network motifs: Simple building blocks of complex networks," Science, 298:824-7, 2002.
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