In the absence of these traditional sources of data, demographers sometimes have to rely on alternative options. This is particularly the case when they want to understand the size and dynamics of past populations, including prehistorical ones. In that case, there are no censuses or surveys to rely upon and demographers can only try and infer population dynamics from unusual and incomplete data sources. Such sources have included parish or church registers, which have informed our understanding of the long-term demographic history of European populations and some isolated communities in sub-Saharan Africa, for example.
Demographers have also attempted to learn about populations of the pre-modern era. Generally speaking, it is the information coaxed from skeletal remains that provides the most insight into these past populations. For instance, it can yield information on the age at death in such populations (e.g., Carbon 14 dating). This branch of demography focusing on pre-modern populations is often referred to as "paleodemography". Together with our key understanding of the dynamics of populations (i.e., the balancing equation), these unconventional data sources permit retracing the history of populations in the (very) distant past