Allometry is the study of size and its consequences. The study of allometry is fundamental to understanding how animals' shape, physiology, life history, and even behavior change with changing body size. Allometric studies focus on comparisons both across species and within species, to test hypotheses about adaptation, to discover how body size helps determine animals' form and function, and to control for the impact of body size when comparing form and life-history characters. Allometric analyses are essential for reconstructing body size from skeletal remains, and also play an important role in understanding how shape changes with growth.