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I am sure of only one thing. When we look at the glory of stars and galaxies in the sky and the glory of forests and flowers in the living world around us, it is evident that God loves diversity. Perhaps the universe is constructed according to a principle of maximum diversity.

--Freeman Dyson

Over the next month, nearly 20,000 students will report to M.D. degree-granting medical schools in the United States for their first day of class. This represents an enrollment increase of nearly 25 percent in just 10 years.

One of the goals of many new and expanding medical schools has been to increase the numbers of underrepresented minorities. Such policies are generally promoted to compensate for past discrimination and to ensure greater similarity between patient populations and health professionals. But diversity and the grounds for supporting it run far deeper.

In fact, if there is a proposition on which we should tolerate very little diversity of opinion, it is this: Diversity is a matter of the utmost importance. From individual minds and communities of learners to whole professions, cultures, and ecosystems, we need diversity, and we need more of it. Diversity is the wellspring of our creativity and resilience. Without it, our lives would become not only monotonous but, in the words of one of the founding philosophers of the enlightenment, Thomas Hobbes, "solitary, poor, and short."

The word diversity comes from the Latin roots meaning "to turn aside." The same root gives us the words divert and diverticulum -- the term physicians use to describe an abnormal out-pouching from a structure such as the bowel or bladder. A diversion is a deviation from the expected path. By definition, every fundamental innovation, whether in the biological or intellectual arena, represents just such a surprise. Our penchant for safety and predictability sometimes leads us to regard unexpected outcomes as failures. Yet without such surprises, we would never learn anything truly new.

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The idea of diversity has great biological significance. It serves as the foundation for Darwin's theory of natural selection. Without anatomic and physiologic variation, there could be no competition and selection between species. If all organisms were alike, none would be fitter than any other, and there would be no differences in traits for which selection could occur. Darwin also saw the spatiotemporal diversity of the environment as an essential feature in providing many different niches that different species are able to occupy.

Consider a specific example of this evolutionary principle. For most of primate evolution over the past 10 million years or so, brains changed very little. But during the past 1 million years, there has been a marked increase in brain size and complexity in the genus Homo, which includes our species, Homo sapiens. Without this boost in brain power, human beings would not exist. The period during which this rapid brain development occurred coincides with a time of remarkable climatic instability affecting continents such as Africa, the cradle of humanity.

Why would climatic instability affect brain size? So long as our ancestors inhabited an environment with little variation in temperature and rainfall, there was little need for rapid adaptation. But during the past 1 million years, lakes repeatedly formed, dried up, and reformed, and temperatures fluctuated widely, offering a powerful selective advantage to organisms that could adapt quickly to such changes. One way of adapting is to grow or shed fir, but another is to think and innovate, fashioning shelters, clothing, and tools.

This is precisely what our human ancestors seem to have done. They developed techniques for constructing shelters, clothing themselves, hunting different kinds of animals, collecting and storing water, growing and harvesting their own food, and passing on lessons in survival from one generation to another using language. Increasingly diverse spatiotemporal environments favored individuals and groups that demonstrated increased mental capacity. The more unpredictable the environment became, the greater the survival advantage adaptability conferred.

A similar principle applies to the development of individual organisms. Experimental studies of rats and apes have shown that organisms raised in richer, more stimulating environments tend to have more complex brains, as manifested in their neural architecture. Their neurons display more synapses, and their dendritic arbors, the receptive connections between neurons, are more complex. This is true of infants and children, but it is even true in adults. Adults from richer environments also tend to exhibit greater behavioral complexity, including an increased capacity to learn.

These findings are important in our understanding of our brain's ability to withstand insults, a property often referred to as cognitive reserve. Compared to people living in undemanding environments, those who are engaged in intellectually and socially diverse activities appear to be more resistant to brain damage associated with conditions such as Alzheimer's disease and do a better job of maintaining their functional capabilities. Again, enriched environments appear to be neurotrophic - nourishing to the brain.

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An appreciation for the benefits of diversity was a central feature of the work of Elinor Ostrom, the recently deceased co-recipient of the 2009 Nobel Prize in Economics. Studying contemporary human affairs, Ostrom discovered that centrally imposed, one-size-fits-all approaches to solving problems rarely work. In other words, when it comes to a complex, widespread challenge such as water conservation or climate change, the best approaches often involve polycentric action at multiple levels. Responses born of diversity tend to be more robust.

Ostrom argued against putting all of our eggs into one basket. Money is an important resource, but it is only one resource. Making money the sole criterion of planning and assessment in a profession such as medicine or an industry such as healthcare tends to impoverish the culture of any institution that commits to it. A strong academic medical center is not a centrally planned system that brooks no deviation from standard policies and procedures. Instead, it is one that tolerates and even celebrates the existence of multiple zones of innovation.

Conformity can be deceptively appealing, in part because it contributes to the impression that those in charge are doing a good job of getting all their constituencies to align with a single vision. Such consistency can be mistaken for good leadership. But our appetite for making an organization consistent and predictable often threatens its resilience and creativity. Ecosystems and cultures of low diversity tend to be not only boring but brittle, unable to respond creatively to challenges and take advantage of new opportunities.

We need to educate health professionals and promote healthcare cultures that prefer to keep multiple options in view, where learners, teachers, practitioners, and patients know each other well enough to feel comfortable sharing stories of their successes and failures. Each needs to be able to learn how decisions have affected others, including the organization as a whole. We need to populate healthcare with people operating with different incentive systems and evaluating their performance according to different kinds of metrics and appraisals.

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A fully rationalized and efficient system - the holy grail of bureaucracies everywhere - never displays a substantial degree of diversity. If it did, it would not be a bureaucracy. Solutions imposed by central authorities tend to be overly simplistic and insufficiently nuanced. As another Nobel laureate in economics, Friedrich Hayek, argued, it is very difficult for someone making decisions from afar to grasp local conditions. The key to a flourishing culture is to strike a balance between expecting everyone to do the same thing the same way every time and encouraging the exploration of new approaches.

The antithesis of a diversity-promoting approach is statistical process control, the brainchild of the original efficiency expert, Frederick Turner. It is based on the premises that there is one right thing to do and one right way to do it. This renders every deviation from standard operating procedure a failure. Such a system can be great for decreasing error rates in mass production, but it can prove disastrous when applied to communities where creativity is essential. In such contexts, excessive standardization often stifles innovation.

Taking the lessons of biological diversity seriously means attempting to promote an ethos of experimentation, risk taking, and innovation. It also means promoting responsibility. When we decide who to entrust with decision making authority, we should ask two simple questions. First, who has the strongest incentive to get the decision right? Second, who will bear the costs of any mistakes? The best decisions are likely to be reached by those who are most responsible, the ones who deal with the situation on a daily basis and who will live with the consequences.

Above all, we need to guard against the impulse to impose simple solutions on complex problems. As physicians know all too well, panaceas frequently fail. Pathology consists not of one disease but hundreds of diseases, which in turn manifest differently in different patients. One-size-fits-all solutions are not just ineffective but often counterproductive. An organization of clones will be rife with redundancy, while a diverse organization stands to reap the rewards of complementarity. By prizing diversity, we promote not only success but humanity's full breadth and richness.

At this time of year, when a record number of new students are commencing their medical studies, the opportunity for reflection and conversation around diversity could hardly be timelier. The increased presence of underrepresented minorities is an important aspect. But diversity itself, and the reasons for promoting it, run far deeper.

In the final analysis, diversity is not primarily a compliance issue, attempting to meet minimum standards for the presence of a particular racial, ethnic, or religious group. Ultimately, diversity is an excellence issue, concerning the full expression of human potential.