The idea of ecological communities has changed tremendously over the past 40 years. The classical view stated that there were so many different species because evolution packed them tightly into the available niches. The modern view emphasizes the idea of trophic cascades, or top-down control in food chains. This emphasized the importance of predation in ecology, although it downplayed the significance of food webs, which showed the interrelated nature of ecosystems better than simple food chains.