 Complex systems are inherently dynamic systems, meaning they are continuously changing over time. Biological systems are a good example of this. The only time they are not engaged in some process of development is when they cease to exist. This is in strong contrast to linear systems that inherently gravitate towards some equilibrium state where they will remain static unless perturbed by some external force. Linear systems theory is the backbone to modern science and engineering that has created our industrial economies. Within this paradigm, technologies are designed to operate at some kind of normal static equilibrium within a well-known and predefined environment. Their life cycle is a linear one where the system is created, put into its operating environment where it is designed to function within some normal set of parameters at a stable and static equilibrium. It is, importantly, designed to resist change and maintain operations within these parameters for as long as possible before being disposed of. This model works well for simple linear systems like bridges where when we clamp our girders together we don't want our bolts to stay there, we don't want them to answer back, to change or grow in any way. But in complex systems, we are not dealing with bolts. We're dealing with components that have some degree of autonomy and capacity for adaptation. People, businesses, stock prices, web applications, smartphones, these things have their own internal logic through which they adapt to changes within their local environment. Sometimes this logic is very simple, such as some financial algorithm that will automatically sell or buy stock at a certain price, or sometimes it is very complex, such as why a person buys a particular item of fashion over another. The net result, though, is that the system can change and is not determined to follow a linear life cycle from cradle to grave. It can learn, grow and adapt in response to internal and external conditions in order to renew itself, that is, to become more or less sustainable and thus alter its life cycle. That is all quite abstract, so let's take some examples. Most businesses don't last very long, less than a few decades. There are many reasons why this might be, but one model to capture the underlying dynamics of how a business evolves is called the Explore and Exploit algorithm. In its early years, a business may explore many different products or services, being able to pivot, remain flexible and diversified. But as the business develops, there will be a few products that prove most lucrative and the business may likely scale them up, becoming centered around them and developing a more formal structured management system as they leverage economics of scale. The result of exploiting a few lucrative products will be that the company will become more profitable, but it is also self-organized into a more critical state. Some small change in the market that moves against the business's core product might destroy the enterprise. Now let's take an example of a business that has designed an alternative course of development for itself. Google, has since its inception, generated over 90% of its revenue from its one core service of web search. So why then does it develop and maintain a whole suite of products that generate relatively little revenue? One theory is that Google knows that in a rapidly evolving market, it needs to be where the next great thing is going to happen. Whether it is in social media or video sharing, by creating this diversity, by continuing to invest resources gained from exploiting its core service into exploring and generating variety, it is able to better evolve and ensure its sustainability. Because markets change, because the climate changes, because everything changes, to design sustainable systems is to design systems that build change and evolution into their structure. To better understand this process of evolution, let's break it down to see how it works. There are just a handful of key components. Firstly, we need to be able to create some variety, then allow for adaptation, and lastly, perform selection to see which of the elements is best suited to the particular environment. Firstly, in the production of variation, the system has to create many diverse types. In biological systems, this is done by mixing and deformation of genes. In the formal world of product development, this typically happens in R&D labs, but when we harness the power of co-creation, we have a new resource for mixing and remixing to create endless diversity. Secondly, adaptation. These diverse types are put into operation to interact and adapt to the environment. This requires that we give the elements the space or autonomy required for them to be able to interact and adapt under their own logic to their own local environment. Lastly, selection. A process of selection is performed on the elements in order to select the so-called fittest, that is, the most suited to that particular environment. In design, this means building feedback loops such as user rating systems so as to determine which products or services are truly functioning best for the end user. Thus, when we are designing, we need to be aware of the trade-off between the two different models. At one end of the spectrum, we have our traditional linear systems that will likely be easier and quicker to design, requiring less of an investment and often operating more efficiently in the short run, but they will be subject to a linear decaying life cycle as they try to externalize change. At the other end of the spectrum, we have evolutionary systems that internalizes change, harnessing the mechanism of evolution to maintain sustainable, cyclical life cycle for an indefinite period of time. In summary then, the key takeaway from this section is that complex systems operate in a constant state of change. Whether we're talking about social networks, airports, or emerging economies, to be able to change as fast as change itself means internalizing this through the integration of evolutionary mechanisms into the platforms that we are building. Evolution is not a mystical process that only happens in natural environments. It is a key feature of dynamic systems, whether we are aware of it or not. But by being conscious of it, we can harness it in our design to create systems that have a sustainable and cyclical life cycle.