First efforts to place development and evolution in a quantitative

First efforts to place development and evolution in a quantitative

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First efforts to place development and evolution in a quantitative, descriptive context were provided by d'Arcy Thompson in On Growth and Form . Using simple rules of geometric transformation he showed that one could obtain the varied forms of organisms by "warping" or "bending" the relative positions of their body parts (see fig. 21.10, pg. 599). These types of diagrams are helpful in identifying what changes of form have taken place, but they do not identify how developmental mechanisms have evolved (the same criticism might be leveled towards Raup's computer snails (see figures 13.7 and 13.8, pgs. 356-357), butmechanism was not the intention of these approaches). One thing Thompson and Raup's diagrams did contribute was to focus attention on the notion of size and shape . These two very simple words are deceptively complex in the context of the evolution of development. A general paleontological pattern
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Unformatted text preview: is Cope's rule which states that the body sizes of species in a lineage of organisms tend to get bigger through time. Horse evolution is a classic example. But what happens when you get bigger? In most cases body parts do not grow at the same rate, thus we have allometry . Allometric growth is the differential rates of growth of two measurable traits of an organism (often it is described as size-correlated changes in shape). It is quantified as y = bxa where x is the measure of one trait, b is a constant, a is the allometric coefficient and y is the other trait. In this form it describes a logarithmic relationship. It can be made into a linear relationship by taking the logs of the values measured for each trait (or by plotting on log x log graph paper):...
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