Allometric Relationships from Evolutionary Pressure

Prediction is very difficult, particularly about the future. 

Allometry is defined as the change of proportions with an increase in the size of a single species or between adults of related groups (Li, 2000). Allometric relations only exist when there is similarity of structure and function between biological units of different size. If completely different mechanisms are involved (e.g., the locomotion of bacteria compared to horses), then no allometric relationship would be expected. 

There appear to be universal biological principles at work in scaling relationships, although the natures of these principles have not yet been fully explored. Allometric relationships among very divergent species seem to be scaled with body mass to some simple multiples of one-quarter power Thus (Brown et al., 2000), 

The radii of mammalian aortas and radii of tree trunks 

The circulation time of mammal blood, and of tree sap, and the cycle time of respiratory, cardiac, gestation, postembryonic development, life span 

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