Final answer:
Brian Arthur posits that systems gain complexity through the addition of diversity, which contributes to more variable interactions and outcomes within the system.
Step-by-step explanation:
According to Brian Arthur, systems become more complex by adding diversity to them. Complexity in systems emerges not just from the number of components but also from the variety of elements and interactions between them. This variety allows for numerous possible combinations and interactions, which can lead to complex behavior even when the individual components are simple. As diversity increases within a system, it leads to a higher level of complexity because there are more distinctive parts and possible interactions that can occur. This can apply to various types of systems, from natural ecological systems to the complex world of technology and social organizations.