The term bioarchaeology has been attributed to British archaeologist Grahame Clark who, in 1972, defined it as the study of animal and human bones from archaeological sites. Redefined in 1977 by Jane Buikstra, bioarchaeology in the United States now refers to the scientific study of human remains from archaeological sites, a discipline known in other countries as osteoarchaeology, osteology or palaeo-osteology. Compared to bioarchaeology, osteoarchaeology is the scientific study that solely focus on the human skeleton. The human skeleton is used to tell us about health, lifestyle, diet, mortality and physique of the past. Furthermore, palaeo-osteology is simple the study of ancient bones. In contrast, the term bioarchaeology is used in Europe to describe the study of all biological remains from archaeological sites. Although Clark used it to describe just human remains and animal remains (zoology/archaeozoology), increasingly modern archaeologists also include botanical remains (botany/archaeobotany) Bioarchaeology was largely born from the practices of New Archaeology, which developed in the United States in the 1970s as a reaction to a mainly cultural-historical approach to understanding the past. Proponents of New Archaeology advocated using processual methods to test hypotheses about the interaction between culture and biology, or a biocultural approach. Some archaeologists advocate a more holistic approach to bioarchaeology that incorporates critical theory and is more relevant to modern descent populations. If possible, human remains from archaeological sites are analyzed to determine sex, age, and health. which all fall under the term 'Bioarchaeology'. Paleodemography Paleodemography is the field that attempts to identify demographic characteristics from the past population. The information gathered is used to make interpretations. Bioarchaeologists use paleodemography sometimes and create life tables, a type of cohort analysis, to understand the demographic characteristics (such as risk of death or sex ratio) of a given age cohort within a population. Age and sex are crucial variables in the construction of a life table, although this information is often not available to bioarchaeologists. Therefore, it is often necessary to estimate the age and sex of individuals based on specific morphological characteristics of the skeleton. Age estimation The estimation of age in bioarchaeology and osteology actually refers to an approximation of skeletal or biological age-at-death. The primary assumption in age estimation is that an individual's skeletal age is closely associated with their chronological age. Age estimation can be based on patterns of growth and development or degenerative changes in the skeleton. Many methods tracking these