The measurement of biological shape change

Biologists are interested in living things. Morphologists are interested in the shape of living things, the differences in shape between living things, and the transformation of one shape into another.

In recent years there have been a number of developments in techniques for shape description in areas outside the biological sciences, stimulated, in part, by developments in image processing technology. It is now a relatively simple and inexpensive task to extract and store a closely placed series of Cartesian coordinates taken from the outline of a structure using an inexpensive video-digitizer. This newly available technology has led biologists to try various new means for form description which will allow more information derived from the outline data to be compared or studied than permitted by previous methodology (O'Higgins and Johnson, 1988).

Before one can compare forms one must describe them. The descriptions may be purely subjective, in which case the comparisons between forms are also subjective. The trend, however, is toward more objective studies, which implies a quantitative method of form description. There are many ways in which form may be described. Some of these are particularly relevant to biological material, for example, distances between “homologous landmarks”: others, such as measures of perimeter, curvature in outline, and so on, are equally applicable to biological or nonbiological material.