Niles Eldridge, one of the world's leading experts in vertebrate fossils, explains basic evolutionary process in his article "Evolution and Environment." He contends that the basis for the process of evolution begins in an organism's local environment. Populations must constantly battle the forces of nature and finds ways around starvation, predators, and disease. The individuals whose inherited characteristics allow them to survive will be the ones most likely to reproduce and pass on the successful characteristics. This natural selection is always taking place in order to create a species better adapted to its surroundings. However, changes in the environment typically occur in a cycle and the ecosystems tend to remain stable. Under normal conditions, natural selection will not have enough time to push a species toward drastic evolutionary modifications. Disruptions in the ecosystem, such as rapid climate change, are the solution. A severe disruption can isolate organism populations and produce various extinctions. Natural selection will then lead to the rapid evolution of the better adapted species. For example, the well adapted mammals were able to emerge and multiply after the extinction of the dinosaurs.