Complexity science, or complex systems, is a new approach to science that studies how relationships between parts give rise to the collective behaviors of a system, and how the system interacts and forms relationships with its environment. Complex adaptive systems are a subset of complex systems. They are adaptive in that their individual and collective behavior changes as a result of experience. Examples of complex adaptive systems include the stock market, social insect and ant colonies, the biosphere and ecosystems, the brain and the immune system, and numerous types of human groups, organizations and communities. Complexity-science consultants apply insights from the study of complex systems in nature, society and science to human organizations.