Jun 02 2012

Morphometrics

Published by at 3:38 pm
Under Environmental Genomics | Molecular Biology


“There are two possible outcomes: if the result confirms the hypothesis, then you’ve made a measurement. If the result is contrary to the hypothesis, then you’ve made a discovery. —Enrico Fermi


A few months after his death in 1528, Vier Bücher von menschlicher Proportion (“The Aesthetic Anatomy of Human Proportion”) by German artist Albrecht Dürer was published in Nuremberg. This work, written, illustrated and designed by Dürer, with woodcuts on virtually every page, was the first book to discuss the problems of comparative and differential anthropometry. The classic aesthetic treatises of Villard de Honnecourt, Vitruvius, Alberti and da Vinci influenced Dürer, however, Dürer’s study of the different human physiques—fat, thin, tall, short, baby, child and adult —was entirely original.

Dürer held that the essence of true form was the primary mathematical figure (e.g., straight line, circle, curve, conic section) constructed arithmetically or geometrically, and made beautiful by the application of a canon of proportion. However, he was also convinced that beauty of form was a relative and not an absolute quality; thus, the purpose of his system of anthropometry was to provide the artist with the means to delineate, on the basis of sheer measurement, all possible types of human figures.

Albrecht Dürer, German Northern Renaissance Painter and Engraver, 1471-1528

Generally, morphometrics (from the Greek: “morph,” meaning shape or form, and “metron,” meaning measurement) comprises methods of extracting measurements from shapes. In most cases applied to biological topics in the widest sense. Schools of morphometrics are characterized by what aspects of biological “form” they are concerned with, what they choose to measure, and what kinds of questions they ask of the measurements once they are made. In many cases involves calculating angles, areas, volumes and other quantitative data from landmark and segmentation data.

Auxology is a meta-term covering the study of all aspects of human physical growth; though, it is also a fundamental of biology, generally. Auxology is a highly multi-disciplinary science involving health sciences and medicine (pediatrics, general practice, endocrinology, neuroendocrinology, physiology, epidemiology), and to a lesser extent nutrition, genetics, anthropology, anthropometry, ergonomics, history, economic history, economics, socioeconomics, sociology, public health, and psychology, among others.

Directly observable characters —such as the shape, size, and color of the body and its parts —were formerly the only means of classifying individuals and populations. They have several disadvantages for this purpose, particularly their complex inheritance, and the fact that almost every character is influenced both by heredity and by environment.

Although they have, for these reasons, largely been superseded for purposes of classification by the blood groups and other hereditary genomic markers; it must be kept in mind that they are still the means by which, in everyday life, we recognize people. We should also recall that quantitative observations of them are the only means we have of comparing skeletal material and observations made on the living before the discovery and application of the blood groups, with people living today. They also present very clear indications of probable natural selection in relation to the environment.

They must therefore continue to be observed with as much precision as possible. It would be a great advantage if their heredity could be more fully understood. It is now clear that almost any one single character, such as stature, is the effect of genes at a considerable number of different loci, so that they are known as polygenic characters.

Developmental noise is defined as perturbations in the developmental environment that arise from random fluctuations at the molecular and cellular level and canalization is the buffering of development against many, if not all of those perturbations. There is currently a bit of a debate as to whether canalization and developmental stability are the same thing. Arguing against this is the fact that canalization reduces the effects of environmental and genetic insults and thereby reduces variation. (1,2) It is sometimes the practice to speak of homeorhesis (“stabilized flow”) a phrase coined by Waddington, (3) and encouraged by others (4) to describe a sort of a developmental trajectory, distinct from canalization, that refers to the capacity for a structure to develop along an ideal developmental trajectory under a particular set of environmental conditions. The sensitivity to random perturbations —or developmental noise— can be viewed as the tendency of a developmental system to produce a morphological change in response to these perturbations and is often called developmental instability.

  1. Wilmore KE and Hallgrimsson B. Within Individual Variation. In: Variation, A central concept in Biology. Elsevier Academic Press. London (2005)
  2. Van Valen L. A study of fluctuating asymmetry. Evolution, 16. (1962).
  3. Waddington, C. H. (1957). The Strategy of the Genes. London: George Allen & Unwin.
  4. Zakharov, V. M. 1992. Population phenogenetics: Analysis of developmental stability in natural populations. Acta Zool. Fenn. 191: 7-30.

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