Five years ago, when I started working for my current employer, the entire organization (about 30 people) consisted only of 20-something white straight single males. The atmosphere was what you would expect from such an environment: conversations on football/soccer, lewd jokes, the smell of beer, and trash in every corner. In short, the perfect place to work, if you were a 20-something white straight single male.
Then the organization started changing. The subculture of 20-something white straight single males in our region could not keep up with the rapid growth of our company. And so the women arrived. And the married guys. And people with kids. And people older than 40. And people from all sorts of ethnic, religious, sexual, and disabled minorities. Before we knew it, the organization had grown to 200 people, and the group of 20-something white straight single males had dwindled to just another minority. And it's still a great place to work, particularly for the large majority of people representing one or two minorities.
Diversity is Important In biological ecosystems, genetic diversity is one of the most important principles. Biodiversity (the variation of species) is the most obvious form of it, but there's also diversity within species themselves. Did you know that honey bees are slightly different from each other? That's how they regulate the temperature in their beehives. When a hive gets too cold, the bees start huddling together, buzzing their wings. And when it gets too hot, the bees spread out and they start fanning their wings. Now, when the bees would respond to the same specific temperatures, they would all start buzzing or fanning their wings at the same time, resulting in a wildly oscillating temperature in the hive. Therefore, to improve stability, nature has made sure that the bees respond to different temperature levels. When the temperature rises, one by one the bees will start fanning their wings. And the more bees join in, the slower the temperature will rise, until it stops completely. Diversity among bees smoothes and stabilizes the temperature in the beehive.
Diversity (officially: heterogeneity) in a complex system is important because the many benefits far outweigh the costs (of variation within the system). Scientists have found that diversity can stabilize a system, and make it resilient to environmental changes. Diversity helps a system to survive in tough environments. It increases flexibility, and it feeds innovation.
The Average is Useless Diversity also means that, in a complex system, you cannot use averages. A thousand clones of one average honey bee cannot ensure stability in the beehive. Or consider this other example: there is no average virus that gives you the common cold. There are at least 200 known virusses that can give you a cold, and probably even more unknown ones. This diversity is the viral system's way of being successful in making you sick, year after year.
Jim Coplien and Neil Harrison listed Diversity as a pattern in Organizational Patterns of Agile Software Development. They recognized that diversity is a good way to stimulate innovation, and the ability to find solutions to problems. Tom DeMarco and Timothy Lister, in PeopleWare: Productive People and Teams, named the Uniform Plastic Person as diversity's anti-pattern. They referred to the problem of managers trying to impose uniformity on people and teams.
Cultivate Variation, Not Uniformity Managers have the tendency to hire lookalikes of themselves, as pointed out by John Maxwell in The 21 Irrefutable Laws of Leadership. The 20-something white straight single males will typically hire other 20-something white straight single males, simply because they can get along so well. It's a natural thing, easily explained by the selfish-gene theory, put forward by Richard Dawkins in his book The Selfish Gene. Our genes have programmed us to favor other people with copies of the same genes, and to dislike others whose DNA differs more. Over tens of thousands of years our genes have been busy waging wars against each other, and they turned us into bigots.
Unfortunately, our genes don't care about the success of our software projects, but we do! Favoring similar people is a trap that managers must try to avoid. That's why I nowadays prefer new people with different educations, experiences, skin colors, ages, genders, personalities, and you-name-it. It's how I try to enforce stability, flexibility, resilience and innovation in our projects. We came a long way from having only 20-something white straight single males. Our teams are a lot more colorful now. Still, I have not been able to find sufficient representatives for various mental disorders, myself not included. But we keep looking.