 Past population levels and habitable ranges of humans or plants and animals may be used to find evidence of past differences in climate for the region.Palynology, the study of pollens, can show not only the range of plants and to reconstruct possible ecology, but to estimate the amount of precipitation in a given time period, based on the abundance of pollen in that layer of sediment or ice.Changes in East African climate have been associated with the evolution of hominini.