Enlarge / Early Man had a sweet mullet. (Photo By DEA PICTURE LIBRARY/De Agostini/Getty Images) (credit: Getty Images / DEA Picture Library) While natural selection is a big part of evolution, the theory now embraces much more than that. One of the big concepts that explains a lot of the pattern of evolution throughout history is called "adaptive radiation." Adaptive radiation is a process in which environmental changes create new resources, challenges, and environmental niches, enabling rapid diversification of organisms from a single ancestral species. Adaptive radiation provides a sound explanation that captures the effects of the interactions among organisms on species diversification.