Friday, February 10, 2006


[evomech] Why Some Animals Have Smaller Eyes: Lifestyle Matters (PR + Article)


1) Why Some Animals Have Smaller Eyes: Lifestyle Matters (Medical News)

If brain size is proportional to body size in virtually all vertebrate animals, Cornell University biologists reasoned, shouldn't eye size and body size scale the same way? While they failed to find a one-size-fits-all rule for eyes, what they learned about the 300 vertebrates they studied helps to explain how animals evolved precisely the orbs they need for everyday life. The biologists reported their findings in the journal Vision Research (August 2004, "The allometry and scaling of the size of vertebrate eyes").

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2) The allometry and scaling of the size of vertebrate eyes

[Howland et al., Vision Research, Aug '04]

We compiled data from the literature and colleagues to examine the relationship between eye axial length and body weight for vertebrates as well as birds, mammals, reptiles, and fishes independently. After fitting the data to logarithmic and semi-logarithmic models, we found that axial length of vertebrate eyes does obey a conventional logarithmic relationship with body weight rather than a semi-logarithmic relationship as Suggested by the results of previous Studies (Handbook of Sensory Physiology, VII/5: The Visual System in Vertebrates, Springer-Verlag, Berlin, 1977; The Allometry of the Vertebrate Eye, Dissertation, University of Chicago, UMI, Ann Arbor, T28274, 1982). The regression slopes and intercepts appear to be characteristic of various animal groups. The axial length of the eye is largest in birds and primates, smaller in other mammals (especially rodents) and reptiles, and widely varying in fishes.

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Model of an Internal Evolutionary Mechanism

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