Emergence is a notoriously slippery subject. Some say it seems to be nothing more than a shorthand way of describing the development of the universe and the rise of life on Earth. Others say it takes one into much deeper scientific and philosophical waters.

Charles Darwin might have articulated the most well-known scientific theory of emergence — evolution — in The Origin of Species. In the famous closing lines of his book, he wrote of his wonder that "from so simple a beginning endless forms most beautiful and most wonderful have been, and are being, evolved.”

Darwin aside, there is little doubt that common objects — snowflakes, for example — are examples of emergence.

Probe a little deeper into the literature on emergence and one can see there is a rich debate and discussion being conducted between and among scientists and philosophers. Those thinking about emergence are, to varying degrees, hopeful that a better understanding of emergence will lead to a richer understanding of cosmic and biological evolution — or, more to the point, a better understanding of who we are as human beings.

"In the recent history of the cosmos, life and eventually mind arose spontaneously from matter on this planet, and in the recent history of biological evolution, symbolic abilities and ethical experience dawned in one species,” said Terrence Deacon, a professor of biological anthropology and linguistics at the University of California, Berkeley. "Quite simply, the history of the world exhibits the emergence of these phenomena. So it isn't such a leap to think that this is also the best clue to understanding them. Ultimately, I feel confident that if we follow this clue, don't give up the quest prematurely and don't settle for pat pseudo answers, we will develop an understanding that is both useful and enlightening,” he said.

Seeking the middle ground

The modern interest in emergence began a century ago when it was offered as a way to navigate between vitalism and reductionism. "There was a three-way controversy in the 1920s,” said Nancey Murphy, a professor of Christian philosophy at Fuller Theological Seminary in Pasadena, Calif. "The vitalists were saying that you had to postulate a vital force or an entelechy — which I think is just another word for an Aristotelian form — in order to understand how you can get life out of nonliving material. That view has been as thoroughly rejected as anything can be in philosophy. The second possibility was that reductionism is true, and you could eventually explain living processes in simple, biochemical terms. The third suggestion was the postulation of emergence — that you get something genuinely new when you get to the level of life,” she said.

In the 1920s, British emergentist C. D. Broad said that the debate between reductionism and emergence in science really boiled down to whether matter — and reality itself — is arranged into different levels in which higher levels of increasing complexity are not reducible to lower levels. Others add, too, that these higher-level laws or properties have causal — or top-down — power over the lower-level laws and properties.

"Technically, Darwinism is an example of weak downward causation,” said Paul Davies, a professor of natural philosophy in the Australian Centre for Astrobiology at Macquarie University. "The law of increasing complexity, if derivable from bottom-level laws, would be merely another weakly emergent law. I am suggesting that there is maybe a strongly emergent law of increasing complexity. Thus, neo-Darwinism might be adequate for biology, or inadequate but augmented by laws of complexity that are only weakly emergent — the position of [biochemist Christian de Duve] and maybe [paleobiologist Simon Conway Morris] — or require strongly emergent laws in addition.”

Among those who think about emergence, said Australian philosopher David J. Chalmers, two main positions have developed: strong emergence and weak emergence. Supporters of weak emergence make the claim that the more fundamental theory can in principle explain the phenomena of the higher-level theory. And many also argue that emergent laws and properties, even if they do exist, don't cause anything on a lower level of reality to change in any way.

"The sense of emergence that I approve of is what I've called innocent emergence,” said Daniel C. Dennett, director of the Center for Cognitive Studies and Austin B. Fletcher Professor of Philosophy at Tufts University in Medford, Mass. Dennett said his definition of an emergent phenomena "is one that is startling, surprising, one that allows us to use a higher-level description to characterize it, but it's not in principle unpredictable or irreducible or anything like that.”

Those who favor strong emergence, meanwhile, search for examples of emergence where the emergent property, or alleged law, cannot be reduced in this way. To use a common emergentist phrase, the whole really is greater than the sum of the parts — and the whole really causes things to happen among lower-level parts. "In the broadest sense, as elements combine into complex structures, new properties emerge that are surprising and not present in earlier, simpler stages, that new things come about through the appearance of complex structures,” said William Hasker, an emeritus professor of philosophy at Huntington University in Huntington, Ind. "As such, these new things are not added from the outside but through the complex structure itself.”

Science to the rescue

Supporters of weak emergence say that stronger forms leave the door open to an unwarranted intrusion of religion into science, even though many atheists also believe in strong emergence. More pointedly, they also argue that emergence can become a science stopper.

"Sad to say, most of the people who use the concept of emergence have something much more mysterious in mind, maybe even mystical, and I don't think that's useful at all,” said Dennett. "I think that calling a phenomenon emergent should be the introduction to a [causal] investigation to understand what the property is and how it emerges and what causes it. If you just think you're explaining it by saying it's emergent or you're just excusing yourself from the investigation, you're only causing trouble. You're not helping,” he said.

Scientists like Paul Davies are taking up Dennett's challenge. They want to put notions of strong emergence to the test. "I long ago became exasperated that defenses of emergence were mostly just talk and propaganda and philosophy, with little or no science,” Davies

said. "I have tried to focus the subject onto the question of whether emergence ultimately makes a difference, that is, does it have real effects that are not contained in the bottom-level laws already. Weak emergence will keep philosophers busy talking for a long time, but only strong emergence makes a real difference scientifically,” Davies said.

In the journal Complexity, Davies recently published a paper — the product of feedback from John D. Barrow, Leonard Susskind and others — in which he proposed a scientific test for strong emergence. The idea is to show that causal closure — the belief that physical events only have physical causes — is false. If so, then non-physical causes become a possibility.

"We are a long way from demonstrating causal closure scientifically and, as I have argued in my paper, there are sound scientific reasons for questioning it,” Davies said. "At the end of the day, we need to find experimental tests of these competing positions, or this stuff is all just words and politics. I propose just such a test in the form of a quantum mechanical experiment involving 400 entangled particles,” he said, adding that he hoped that scientific advances will allow the experiment to be carried out within the next few decades.

Evolution gets deep

Scientists and philosophers engaged in emergence research remain committed to the long-standing emergentist view that reductionism and vitalism — defined as life and mind entities or forces — are both inadequate approaches for explaining past, present and future evolution.

If emergence is to make a splash among scientists in the 21st century, then it will have to be fashioned in a far different — and more subtle — form that takes science seriously, said Tim O'Connor, a professor of philosophy at Indiana University. "I do not myself believe that biology as such points to [strong] emergentism,” he said. "Advances in the 20th century uncovering the chemical basis of life makes reductionism here much more plausible now than it seemed at the dawn of that century.”

However, O'Connor said that even on present knowledge, it is possible that there are emergent aspects to living systems. "But if this is so, it would involve a much more subtle manifestation than was envisioned by previous generations of biological emergentists, who posited a picture of the natural world as highly stratified into physical, chemical, biological and psychological layers, each understandable in their own terms,” he said.

Emergence does provide a way of seeing the world, Hasker said. "It doesn't level everything out at the base level — that all there is is atoms bouncing around, a flat materialist view that is pretty limited, pretty sterile, leaves an awful lot out,” he said. On the other hand, he added, it doesn't necessarily require supernatural intervention. "The idea of the natural world becoming more complexly organized somehow generates these new features. I think that is a significant and important way of looking at the world and different than the two extremes,” Hasker said.

Some do take emergence in a more religious direction. Philip Clayton, Ingraham Professor of Theology at Claremont School of Theology and professor of philosophy and of religion at Claremont Graduate University, said that emergence reveals a dynamic world where becoming and novelty trump static being — a view not unrelated to the process thought of philosopher and mathematician Alfred North Whitehead. As Clayton argues in his seminal book, Mind and Emergence, emergence may be a way to explain how God creates and acts within the world.

Some also believe emergence might shed light on the mind-body problem. One of the corollaries of strong emergence is top-down causation — the belief that the wholes are not only more than the sum of the parts but also that the irreducible properties of wholes affect the parts in very real ways. Emergentists generally agree that the most obvious case of top-down causation is the mind — or, as Hasker has said, the soul. Rather than being merely epiphenomenal, emergence theorists like Clayton argue that the mind, as a higher-level emergent property, causes changes to happen within the lower-level brain, which in turn directs the rest of the body.

Hasker offers a distinctly Darwinian explanation for why he thinks this is the case. "What's the evolutionary account for the origin of intelligence?” he asks. "To make sense of that, intelligence has to be something natural selection can work on. But if your thought has no causal influence on what happens physically in your body, no top-down causation, then your thoughts, your consciousness, becomes invisible. Natural selection can only operate on physical structures and behavior. If there's no influence on physical behavior, thought is unaffected by natural selection and you can give no evolutionary explanation on how we have come to be thinking beings,” he said.

Others like Dennett are more optimistic that science will discover a thoroughly reductionistic understanding of the mind that precludes all but innocent emergence. "Two hundred years ago they thought the problem of reproduction was hard, but look, we've solved it,” he said.

Few doubt that emergence remains a promising philosophical concept, but whether it is good science remains to be seen. "Emergence is just a word that may or may not turn out to be useful,” said Murphy. "Whether it turns out to be useful depends upon whether people are going to be clear enough about what they mean by it when they use it. Otherwise is it just going to be sort of the flavor of the year, some new academic jargon.”

If emergence is shown to have some basis in science, O'Connor said it promises to bring the science-and-religion dialogue to a whole new level. "On the one hand, it avoids positing a this-far-and-no-further attitude to the attempt to attain a thorough scientific understanding of the fundamental processes that make up the ongoing lives of the remarkable animals that are human beings. On the other hand, it also serves to remind one of the very partial and ongoing nature of scientific inquiry, encouraging the humility and open-mindedness characterizing the scientific spirit at its noblest.”

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